PL/pgSQL PL/pgSQL is a loadable procedural language for the PostgreSQL database system. This package was originally written by Jan Wieck. This documentation was in part written by Roberto Mello (rmello@fslc.usu.edu). The design goals of PL/pgSQL were to create a loadable procedural language that can be used to create functions and trigger procedures, adds control structures to the SQL language, can perform complex computations, inherits all user defined types, functions and operators, can be defined to be trusted by the server, is easy to use. The PL/pgSQL call handler parses the function's source text and produces an internal binary instruction tree the first time the function is called (within any one backend process). The instruction tree fully translates the PL/pgSQL statement structure, but individual SQL expressions and SQL queries used in the function are not translated immediately. As each expression and SQL query is first used in the function, the PL/pgSQL interpreter creates a prepared execution plan (using the SPI manager's SPI_prepare and SPI_saveplan functions). Subsequent visits to that expression or query re-use the prepared plan. Thus, a function with conditional code that contains many statements for which execution plans might be required, will only prepare and save those plans that are really used during the lifetime of the database connection. This can provide a considerable savings of parsing activity. A disadvantage is that errors in a specific expression or query may not be detected until that part of the function is reached in execution. Once PL/pgSQL has made a query plan for a particular query in a function, it will re-use that plan for the life of the database connection. This is usually a win for performance, but it can cause some problems if you dynamically alter your database schema. For example: CREATE FUNCTION populate() RETURNS INTEGER AS ' DECLARE -- Declarations BEGIN PERFORM my_function(); END; ' LANGUAGE 'plpgsql'; If you execute the above function, it will reference the OID for my_function() in the query plan produced for the PERFORM statement. Later, if you drop and re-create my_function(), then populate() will not be able to find my_function() anymore. You would then have to re-create populate(), or at least start a new database session so that it will be compiled afresh. Because PL/pgSQL saves execution plans in this way, queries that appear directly in a PL/pgSQL function must refer to the same tables and fields on every execution; that is, you cannot use a parameter as the name of a table or field in a query. To get around this restriction, you can construct dynamic queries using the PL/pgSQL EXECUTE statement --- at the price of constructing a new query plan on every execution. Except for input/output conversion and calculation functions for user defined types, anything that can be defined in C language functions can also be done with PL/pgSQL. It is possible to create complex conditional computation functions and later use them to define operators or use them in functional indexes. Better performance (see ) SQL support (see ) Portability (see ) SQL is the language PostgreSQL (and most other Relational Databases) use as query language. It's portable and easy to learn. But every SQL statement must be executed individually by the database server. That means that your client application must send each query to the database server, wait for it to process it, receive the results, do some computation, then send other queries to the server. All this incurs inter-process communication and may also incur network overhead if your client is on a different machine than the database server. With PL/pgSQL you can group a block of computation and a series of queries inside the database server, thus having the power of a procedural language and the ease of use of SQL, but saving lots of time because you don't have the whole client/server communication overhead. This can make for a considerable performance increase. PL/pgSQL adds the power of a procedural language to the flexibility and ease of SQL. With PL/pgSQL you can use all the data types, columns, operators and functions of SQL. Because PL/pgSQL functions run inside PostgreSQL, these functions will run on any platform where PostgreSQL runs. Thus you can reuse code and have less development costs. Developing in PL/pgSQL is pretty straight forward, especially if you have developed in other database procedural languages, such as Oracle's PL/SQL. Two good ways of developing in PL/pgSQL are: Using a text editor and reloading the file with psql Using PostgreSQL's GUI Tool: PgAccess One good way to develop in PL/pgSQL is to simply use the text editor of your choice to create your functions, and in another console, use psql (PostgreSQL's interactive monitor) to load those functions. If you are doing it this way, it is a good idea to write the function using CREATE OR REPLACE FUNCTION. That way you can reload the file to update the function definition. For example: CREATE OR REPLACE FUNCTION testfunc(INTEGER) RETURNS INTEGER AS ' .... end; ' LANGUAGE 'plpgsql'; While running psql, you can load or reload such a function definition file with \i filename.sql and then immediately issue SQL commands to test the function. Another good way to develop in PL/pgSQL is using PostgreSQL's GUI tool: PgAccess. It does some nice things for you, like escaping single-quotes, and making it easy to recreate and debug functions. PL/pgSQL is a block structured language. The complete text of a function definition must be a block. A block is defined as: <<label>> DECLARE declarations BEGIN statements END; Any statement in the statement section of a block can be a sub-block. Sub-blocks can be used for logical grouping or to localize variables to a small group of statements. The variables declared in the declarations section preceding a block are initialized to their default values every time the block is entered, not only once per function call. For example: CREATE FUNCTION somefunc() RETURNS INTEGER AS ' DECLARE quantity INTEGER := 30; BEGIN RAISE NOTICE ''Quantity here is %'',quantity; -- Quantity here is 30 quantity := 50; -- -- Create a sub-block -- DECLARE quantity INTEGER := 80; BEGIN RAISE NOTICE ''Quantity here is %'',quantity; -- Quantity here is 80 END; RAISE NOTICE ''Quantity here is %'',quantity; -- Quantity here is 50 RETURN quantity; END; ' LANGUAGE 'plpgsql'; It is important not to confuse the use of BEGIN/END for grouping statements in PL/pgSQL with the database commands for transaction control. PL/pgSQL's BEGIN/END are only for grouping; they do not start or end a transaction. Functions and trigger procedures are always executed within a transaction established by an outer query --- they cannot start or commit transactions, since PostgreSQL does not have nested transactions. Each statement and declaration within a block is terminated by a semicolon. All keywords and identifiers can be written in mixed upper- and lower-case. Identifiers are implicitly converted to lower-case unless double-quoted. There are two types of comments in PL/pgSQL. A double dash -- starts a comment that extends to the end of the line. A /* starts a block comment that extends to the next occurrence of */. Block comments cannot be nested, but double dash comments can be enclosed into a block comment and a double dash can hide the block comment delimiters /* and */. All variables, rows and records used in a block must be declared in the declarations section of the block. (The only exception is that the loop variable of a FOR loop iterating over a range of integer values is automatically declared as an integer variable.) PL/pgSQL variables can have any SQL data type, such as INTEGER, VARCHAR and CHAR. Here are some examples of variable declarations: user_id INTEGER; quantity NUMERIC(5); url VARCHAR; The general syntax of a variable declaration is: name CONSTANT type NOT NULL { DEFAULT | := } expression ; The DEFAULT clause, if given, specifies the initial value assigned to the variable when the block is entered. If the DEFAULT clause is not given then the variable is initialized to the SQL NULL value. The CONSTANT option prevents the variable from being assigned to, so that its value remains constant for the duration of the block. If NOT NULL is specified, an assignment of a NULL value results in a run-time error. All variables declared as NOT NULL must have a non-NULL default value specified. The default value is evaluated every time the block is entered. So, for example, assigning 'now' to a variable of type timestamp causes the variable to have the time of the current function call, not when the function was precompiled. Examples: quantity INTEGER DEFAULT 32; url varchar := ''http://mysite.com''; user_id CONSTANT INTEGER := 10; name ALIAS FOR $n; Parameters passed to functions are named with the identifiers $1, $2, etc. Optionally, aliases can be declared for $n parameter names for increased readability. Either the alias or the numeric identifier can then be used to refer to the parameter value. Some examples: CREATE FUNCTION sales_tax(REAL) RETURNS REAL AS ' DECLARE subtotal ALIAS FOR $1; BEGIN return subtotal * 0.06; END; ' LANGUAGE 'plpgsql'; CREATE FUNCTION instr(VARCHAR,INTEGER) RETURNS INTEGER AS ' DECLARE v_string ALIAS FOR $1; index ALIAS FOR $2; BEGIN -- Some computations here END; ' LANGUAGE 'plpgsql'; name tablename%ROWTYPE; A variable of a composite type is called a row variable (or row-type variable). Such a variable can hold a whole row of a SELECT or FOR query result, so long as that query's column set matches the declared type of the variable. The individual fields of the row value are accessed using the usual dot notation, for example rowvar.field. Presently, a row variable can only be declared using the %ROWTYPE notation; although one might expect a bare table name to work as a type declaration, it won't be accepted within PL/pgSQL functions. Parameters to a function can be composite types (complete table rows). In that case, the corresponding identifier $n will be a row variable, and fields can be selected from it, for example $1.user_id. Only the user-defined attributes of a table row are accessible in a row-type variable, not OID or other system attributes (because the row could be from a view). The fields of the row type inherit the table's field size or precision for data types such as char(n). name RECORD; Record variables are similar to row-type variables, but they have no predefined structure. They take on the actual row structure of the row they are assigned during a SELECT or FOR command. The substructure of a record variable can change each time it is assigned to. A consequence of this is that until a record variable is first assigned to, it has no substructure, and any attempt to access a field in it will draw a run-time error. Note that RECORD is not a true data type, only a placeholder. Thus, for example, one cannot declare a function returning RECORD. Using the %TYPE and %ROWTYPE attributes, you can declare variables with the same data type or structure as another database item (e.g: a table field). variable%TYPE %TYPE provides the data type of a variable or database column. You can use this to declare variables that will hold database values. For example, let's say you have a column named user_id in your users table. To declare a variable with the same data type as users.user_id you write: user_id users.user_id%TYPE; By using %TYPE you don't need to know the data type of the structure you are referencing, and most important, if the data type of the referenced item changes in the future (e.g: you change your table definition of user_id from INTEGER to REAL), you may not need to change your function definition. table%ROWTYPE %ROWTYPE provides the composite data type corresponding to a whole row of the specified table. table must be an existing table or view name of the database. DECLARE users_rec users%ROWTYPE; user_id users.user_id%TYPE; BEGIN user_id := users_rec.user_id; ... CREATE FUNCTION does_view_exist(INTEGER) RETURNS bool AS ' DECLARE key ALIAS FOR $1; table_data cs_materialized_views%ROWTYPE; BEGIN SELECT INTO table_data * FROM cs_materialized_views WHERE sort_key=key; IF NOT FOUND THEN RETURN false; END IF; RETURN true; END; ' LANGUAGE 'plpgsql'; RENAME oldname TO newname; Using the RENAME declaration you can change the name of a variable, record or row. This is primarily useful if NEW or OLD should be referenced by another name inside a trigger procedure. See also ALIAS. Examples: RENAME id TO user_id; RENAME this_var TO that_var; RENAME appears to be broken as of PostgreSQL 7.2. Fixing this is of low priority, since ALIAS covers most of the practical uses of RENAME. All expressions used in PL/pgSQL statements are processed using the server's regular SQL executor. Expressions that appear to contain constants may in fact require run-time evaluation (e.g. 'now' for the timestamp type) so it is impossible for the PL/pgSQL parser to identify real constant values other than the NULL keyword. All expressions are evaluated internally by executing a query SELECT expression using the SPI manager. In the expression, occurrences of PL/pgSQL variable identifiers are replaced by parameters and the actual values from the variables are passed to the executor in the parameter array. This allows the query plan for the SELECT to be prepared just once and then re-used for subsequent evaluations. The evaluation done by the PostgreSQL main parser has some side effects on the interpretation of constant values. In detail there is a difference between what these two functions do: CREATE FUNCTION logfunc1 (TEXT) RETURNS TIMESTAMP AS ' DECLARE logtxt ALIAS FOR $1; BEGIN INSERT INTO logtable VALUES (logtxt, ''now''); RETURN ''now''; END; ' LANGUAGE 'plpgsql'; and CREATE FUNCTION logfunc2 (TEXT) RETURNS TIMESTAMP AS ' DECLARE logtxt ALIAS FOR $1; curtime timestamp; BEGIN curtime := ''now''; INSERT INTO logtable VALUES (logtxt, curtime); RETURN curtime; END; ' LANGUAGE 'plpgsql'; In the case of logfunc1(), the PostgreSQL main parser knows when preparing the plan for the INSERT, that the string 'now' should be interpreted as timestamp because the target field of logtable is of that type. Thus, it will make a constant from it at this time and this constant value is then used in all invocations of logfunc1() during the lifetime of the backend. Needless to say that this isn't what the programmer wanted. In the case of logfunc2(), the PostgreSQL main parser does not know what type 'now' should become and therefore it returns a data value of type text containing the string 'now'. During the ensuing assignment to the local variable curtime, the PL/pgSQL interpreter casts this string to the timestamp type by calling the text_out() and timestamp_in() functions for the conversion. So, the computed time stamp is updated on each execution as the programmer expects. The mutable nature of record variables presents a problem in this connection. When fields of a record variable are used in expressions or statements, the data types of the fields must not change between calls of one and the same expression, since the expression will be planned using the data type that is present when the expression is first reached. Keep this in mind when writing trigger procedures that handle events for more than one table. (EXECUTE can be used to get around this problem when necessary.) In this section and the following ones, we describe all the statement types that are explicitly understood by PL/pgSQL. Anything not recognized as one of these statement types is presumed to be an SQL query, and is sent to the main database engine to execute (after substitution for any PL/pgSQL variables used in the statement). Thus, for example, SQL INSERT, UPDATE, and DELETE commands may be considered to be statements of PL/pgSQL. But they are not specifically listed here. An assignment of a value to a variable or row/record field is written as: identifier := expression; As explained above, the expression in such a statement is evaluated by means of an SQL SELECT command sent to the main database engine. The expression must yield a single value. If the expression's result data type doesn't match the variable's data type, or the variable has a specific size/precision (as for char(20)), the result value will be implicitly converted by the PL/pgSQL interpreter using the result type's output-function and the variable type's input-function. Note that this could potentially result in run-time errors generated by the input function, if the string form of the result value is not acceptable to the input function. Examples: user_id := 20; tax := subtotal * 0.06; The result of a SELECT command yielding multiple columns (but only one row) can be assigned to a record variable, row-type variable, or list of scalar variables. This is done by: SELECT INTO target expressions FROM ...; where target can be a record variable, a row variable, or a comma-separated list of simple variables and record/row fields. Note that this is quite different from PostgreSQL's normal interpretation of SELECT INTO, which is that the INTO target is a newly created table. (If you want to create a table from a SELECT result inside a PL/pgSQL function, use the syntax CREATE TABLE ... AS SELECT.) If a row or a variable list is used as target, the selected values must exactly match the structure of the target(s), or a run-time error occurs. When a record variable is the target, it automatically configures itself to the row type of the query result columns. Except for the INTO clause, the SELECT statement is the same as a normal SQL SELECT query and can use the full power of SELECT. If the SELECT query returns zero rows, NULLs are assigned to the target(s). If the SELECT query returns multiple rows, the first row is assigned to the target(s) and the rest are discarded. (Note that the first row is not well-defined unless you've used ORDER BY.) At present, the INTO clause can appear almost anywhere in the SELECT query, but it is recommended to place it immediately after the SELECT keyword as depicted above. Future versions of PL/pgSQL may be less forgiving about placement of the INTO clause. There is a special variable named FOUND of type boolean that can be used immediately after a SELECT INTO to check if an assignment had success (that is, at least one row was returned by the SELECT). For example, SELECT INTO myrec * FROM EMP WHERE empname = myname; IF NOT FOUND THEN RAISE EXCEPTION ''employee % not found'', myname; END IF; Alternatively, you can use the IS NULL (or ISNULL) conditional to test for NULLity of a RECORD/ROW result. Note that there is no way to tell whether any additional rows might have been discarded. DECLARE users_rec RECORD; full_name varchar; BEGIN SELECT INTO users_rec * FROM users WHERE user_id=3; IF users_rec.homepage IS NULL THEN -- user entered no homepage, return "http://" RETURN ''http://''; END IF; END; Sometimes one wishes to evaluate an expression or query but discard the result (typically because one is calling a function that has useful side-effects but no useful result value). To do this in PL/pgSQL, use the PERFORM statement: PERFORM query; This executes a SELECT query and discards the result. PL/pgSQL variables are substituted into the query as usual. One might expect that SELECT with no INTO clause would accomplish this result, but at present the only accepted way to do it is PERFORM. An example: PERFORM create_mv(''cs_session_page_requests_mv'','' SELECT session_id, page_id, count(*) AS n_hits, sum(dwell_time) AS dwell_time, count(dwell_time) AS dwell_count FROM cs_fact_table GROUP BY session_id, page_id ''); Oftentimes you will want to generate dynamic queries inside your PL/pgSQL functions, that is, queries that will involve different tables or different data types each time they are executed. PL/pgSQL's normal attempts to cache plans for queries will not work in such scenarios. To handle this sort of problem, the EXECUTE statement is provided: EXECUTE query-string; where query-string is an expression yielding a string (of type text) containing the query to be executed. This string is fed literally to the SQL engine. Note in particular that no substitution of PL/pgSQL variables is done on the query string. The values of variables must be inserted into the query string as it is constructed. When working with dynamic queries you will have to face escaping of single quotes in PL/pgSQL. Please refer to the table in for a detailed explanation that will save you some effort. Unlike all other queries in PL/pgSQL, a query run by an EXECUTE statement is not prepared and saved just once during the life of the server. Instead, the query is prepared each time the statement is run. The query-string can be dynamically created within the procedure to perform actions on variable tables and fields. The results from SELECT queries are discarded by EXECUTE, and SELECT INTO is not currently supported within EXECUTE. So, the only way to extract a result from a dynamically-created SELECT is to use the FOR-IN-EXECUTE form described later. An example: EXECUTE ''UPDATE tbl SET '' || quote_ident(fieldname) || '' = '' || quote_literal(newvalue) || '' WHERE ...''; This example shows use of the functions quote_ident(TEXT) and quote_literal(TEXT). Variables containing field and table identifiers should be passed to function quote_ident(). Variables containing literal elements of the dynamic query string should be passed to quote_literal(). Both take the appropriate steps to return the input text enclosed in single or double quotes and with any embedded special characters properly escaped. Here is a much larger example of a dynamic query and EXECUTE: CREATE FUNCTION cs_update_referrer_type_proc() RETURNS INTEGER AS ' DECLARE referrer_keys RECORD; -- Declare a generic record to be used in a FOR a_output varchar(4000); BEGIN a_output := ''CREATE FUNCTION cs_find_referrer_type(varchar,varchar,varchar) RETURNS VARCHAR AS '''' DECLARE v_host ALIAS FOR $1; v_domain ALIAS FOR $2; v_url ALIAS FOR $3; BEGIN ''; -- -- Notice how we scan through the results of a query in a FOR loop -- using the FOR <record> construct. -- FOR referrer_keys IN SELECT * FROM cs_referrer_keys ORDER BY try_order LOOP a_output := a_output || '' IF v_'' || referrer_keys.kind || '' LIKE '''''''''' || referrer_keys.key_string || '''''''''' THEN RETURN '''''' || referrer_keys.referrer_type || ''''''; END IF;''; END LOOP; a_output := a_output || '' RETURN NULL; END; '''' LANGUAGE ''''plpgsql'''';''; -- This works because we are not substituting any variables -- Otherwise it would fail. Look at PERFORM for another way to run functions EXECUTE a_output; END; ' LANGUAGE 'plpgsql'; GET DIAGNOSTICS variable = item , ... ; This command allows retrieval of system status indicators. Each item is a keyword identifying a state value to be assigned to the specified variable (which should be of the right data type to receive it). The currently available status items are ROW_COUNT, the number of rows processed by the last SQL query sent down to the SQL engine; and RESULT_OID, the OID of the last row inserted by the most recent SQL query. Note that RESULT_OID is only useful after an INSERT query. Control structures are probably the most useful (and important) part of PL/pgSQL. With PL/pgSQL's control structures, you can manipulate PostgreSQL data in a very flexible and powerful way. RETURN expression; The function terminates and the value of expression will be returned to the upper executor. The expression's result will be automatically cast into the function's return type as described for assignments. The return value of a function cannot be left undefined. If control reaches the end of the top-level block of the function without hitting a RETURN statement, a run-time error will occur. IF statements let you execute commands based on certain conditions. PL/pgSQL has four forms of IF: IF-THEN, IF-THEN-ELSE, IF-THEN-ELSE IF, and IF-THEN-ELSIF-THEN-ELSE. IF boolean-expression THEN statements END IF; IF-THEN statements are the simplest form of IF. The statements between THEN and END IF will be executed if the condition is true. Otherwise, they are skipped. IF v_user_id <> 0 THEN UPDATE users SET email = v_email WHERE user_id = v_user_id; END IF; IF boolean-expression THEN statements ELSE statements END IF; IF-THEN-ELSE statements add to IF-THEN by letting you specify an alternative set of statements that should be executed if the condition evaluates to FALSE. IF parentid IS NULL or parentid = '''' THEN return fullname; ELSE return hp_true_filename(parentid) || ''/'' || fullname; END IF; IF v_count > 0 THEN INSERT INTO users_count(count) VALUES(v_count); return ''t''; ELSE return ''f''; END IF; IF statements can be nested, as in the following example: IF demo_row.sex = ''m'' THEN pretty_sex := ''man''; ELSE IF demo_row.sex = ''f'' THEN pretty_sex := ''woman''; END IF; END IF; When you use this form, you are actually nesting an IF statement inside the ELSE part of an outer IF statement. Thus you need one END IF statement for each nested IF and one for the parent IF-ELSE. This is workable but grows tedious when there are many alternatives to be checked. IF boolean-expression THEN statements ELSIF boolean-expression THEN statements ELSIF boolean-expression THEN statements ... ELSE statements END IF; IF-THEN-ELSIF-ELSE provides a more convenient method of checking many alternatives in one statement. Formally it is equivalent to nested IF-THEN-ELSE-IF-THEN commands, but only one END IF is needed. Here is an example: IF number = 0 THEN result := ''zero''; ELSIF number > 0 THEN result := ''positive''; ELSIF number < 0 THEN result := ''negative''; ELSE -- hmm, the only other possibility is that number IS NULL result := ''NULL''; END IF; The final ELSE section is optional. With the LOOP, EXIT, WHILE and FOR statements, you can arrange for your PL/pgSQL function to repeat a series of commands. <<label>> LOOP statements END LOOP; LOOP defines an unconditional loop that is repeated indefinitely until terminated by an EXIT or RETURN statement. The optional label can be used by EXIT statements in nested loops to specify which level of nesting should be terminated. EXIT label WHEN expression ; If no label is given, the innermost loop is terminated and the statement following END LOOP is executed next. If label is given, it must be the label of the current or some outer level of nested loop or block. Then the named loop or block is terminated and control continues with the statement after the loop's/block's corresponding END. If WHEN is present, loop exit occurs only if the specified condition is true, otherwise control passes to the statement after EXIT. Examples: LOOP -- some computations IF count > 0 THEN EXIT; -- exit loop END IF; END LOOP; LOOP -- some computations EXIT WHEN count > 0; END LOOP; BEGIN -- some computations IF stocks > 100000 THEN EXIT; -- illegal. Can't use EXIT outside of a LOOP END IF; END; <<label>> WHILE expression LOOP statements END LOOP; The WHILE statement repeats a sequence of statements so long as the condition expression evaluates to true. The condition is checked just before each entry to the loop body. For example: WHILE amount_owed > 0 AND gift_certificate_balance > 0 LOOP -- some computations here END LOOP; WHILE NOT boolean_expression LOOP -- some computations here END LOOP; <<label>> FOR name IN REVERSE expression .. expression LOOP statements END LOOP; This form of FOR creates a loop that iterates over a range of integer values. The variable name is automatically defined as type integer and exists only inside the loop. The two expressions giving the lower and upper bound of the range are evaluated once when entering the loop. The iteration step is normally 1, but is -1 when REVERSE is specified. Some examples of integer FOR loops: FOR i IN 1..10 LOOP -- some expressions here RAISE NOTICE ''i is %'',i; END LOOP; FOR i IN REVERSE 10..1 LOOP -- some expressions here END LOOP; Using a different type of FOR loop, you can iterate through the results of a query and manipulate that data accordingly. The syntax is: <<label>> FOR record | row IN select_query LOOP statements END LOOP; The record or row variable is successively assigned all the rows resulting from the SELECT query and the loop body is executed for each row. Here is an example: CREATE FUNCTION cs_refresh_mviews () RETURNS INTEGER AS ' DECLARE mviews RECORD; BEGIN PERFORM cs_log(''Refreshing materialized views...''); FOR mviews IN SELECT * FROM cs_materialized_views ORDER BY sort_key LOOP -- Now "mviews" has one record from cs_materialized_views PERFORM cs_log(''Refreshing materialized view '' || quote_ident(mviews.mv_name) || ''...''); EXECUTE ''TRUNCATE TABLE '' || quote_ident(mviews.mv_name); EXECUTE ''INSERT INTO '' || quote_ident(mviews.mv_name) || '' '' || mviews.mv_query; END LOOP; PERFORM cs_log(''Done refreshing materialized views.''); RETURN 1; end; ' LANGUAGE 'plpgsql'; If the loop is terminated by an EXIT statement, the last assigned row value is still accessible after the loop. The FOR-IN-EXECUTE statement is another way to iterate over records: <<label>> FOR record | row IN EXECUTE text_expression LOOP statements END LOOP; This is like the previous form, except that the source SELECT statement is specified as a string expression, which is evaluated and re-planned on each entry to the FOR loop. This allows the programmer to choose the speed of a pre-planned query or the flexibility of a dynamic query, just as with a plain EXECUTE statement. The PL/pgSQL parser presently distinguishes the two kinds of FOR loops (integer or record-returning) by checking whether the target variable mentioned just after FOR has been declared as a record/row variable. If not, it's presumed to be an integer FOR loop. This can cause rather nonintuitive error messages when the true problem is, say, that one has misspelled the FOR variable name. Rather than executing a whole query at once, it is possible to set up a cursor that encapsulates the query, and then read the query result a few rows at a time. One reason for doing this is to avoid memory overrun when the result contains a large number of rows. (However, PL/pgSQL users don't normally need to worry about that, since FOR loops automatically use a cursor internally to avoid memory problems.) A more interesting possibility is that a function can return a reference to a cursor that it has set up, allowing the caller to read the rows. This provides one way of returning a row set from a function. All access to cursors in PL/pgSQL goes through cursor variables, which are always of the special data type refcursor. One way to create a cursor variable is just to declare it as a variable of type refcursor. Another way is to use the cursor declaration syntax, which in general is: name CURSOR ( arguments ) FOR select_query ; (FOR may be replaced by IS for Oracle compatibility.) arguments, if any, are a comma-separated list of name datatype pairs that define names to be replaced by parameter values in the given query. The actual values to substitute for these names will be specified later, when the cursor is opened. Some examples: DECLARE curs1 refcursor; curs2 CURSOR FOR SELECT * from tenk1; curs3 CURSOR (key int) IS SELECT * from tenk1 where unique1 = key; All three of these variables have the data type refcursor, but the first may be used with any query, while the second has a fully specified query already bound to it, and the last has a parameterized query bound to it. (key will be replaced by an integer parameter value when the cursor is opened.) The variable curs1 is said to be unbound since it is not bound to any particular query. Before a cursor can be used to retrieve rows, it must be opened. (This is the equivalent action to the SQL command DECLARE CURSOR.) PL/pgSQL has four forms of the OPEN statement, two of which are for use with unbound cursor variables and the other two for use with bound cursor variables. OPEN unbound-cursor FOR SELECT ...; The cursor variable is opened and given the specified query to execute. The cursor cannot be open already, and it must have been declared as an unbound cursor (that is, as a simple refcursor variable). The SELECT query is treated in the same way as other SELECTs in PL/pgSQL: PL/pgSQL variable names are substituted for, and the query plan is cached for possible re-use. OPEN curs1 FOR SELECT * FROM foo WHERE key = mykey; OPEN unbound-cursor FOR EXECUTE query-string; The cursor variable is opened and given the specified query to execute. The cursor cannot be open already, and it must have been declared as an unbound cursor (that is, as a simple refcursor variable). The query is specified as a string expression in the same way as for the EXECUTE command. As usual, this gives flexibility for the query to vary from one run to the next. OPEN curs1 FOR EXECUTE ''SELECT * FROM '' || quote_ident($1); OPEN bound-cursor ( argument_values ) ; This form of OPEN is used to open a cursor variable whose query was bound to it when it was declared. The cursor cannot be open already. A list of actual argument value expressions must appear if and only if the cursor was declared to take arguments. These values will be substituted into the query. The query plan for a bound cursor is always considered cacheable --- there is no equivalent of EXECUTE in this case. OPEN curs2; OPEN curs3(42); Once a cursor has been opened, it can be manipulated with the statements described here. These manipulations need not occur in the same function that opened the cursor to begin with. You can return a refcursor value out of a function and let the caller operate on the cursor. (Internally, a refcursor value is simply the string name of a Portal containing the active query for the cursor. This name can be passed around, assigned to other refcursor variables, and so on, without disturbing the Portal.) All Portals are implicitly closed at end of transaction. Therefore a refcursor value is useful to reference an open cursor only until the end of the transaction. FETCH cursor INTO target; FETCH retrieves the next row from the cursor into a target, which may be a row variable, a record variable, or a comma-separated list of simple variables, just as for SELECT INTO. As with SELECT INTO, the special variable FOUND may be checked to see whether a row was obtained or not. FETCH curs1 INTO rowvar; FETCH curs2 INTO foo,bar,baz; CLOSE cursor; CLOSE closes the Portal underlying an open cursor. This can be used to release resources earlier than end of transaction, or to free up the cursor variable to be opened again. CLOSE curs1; Use the RAISE statement to report messages and raise errors. RAISE level 'format' , variable ...; Possible levels are DEBUG (write the message into the postmaster log), NOTICE (write the message into the postmaster log and forward it to the client application) and EXCEPTION (raise an error, aborting the transaction). Inside the format string, % is replaced by the next optional argument's external representation. Write %% to emit a literal %. Note that the optional arguments must presently be simple variables, not expressions, and the format must be a simple string literal. Examples: RAISE NOTICE ''Calling cs_create_job(%)'',v_job_id; In this example, the value of v_job_id will replace the % in the string. RAISE EXCEPTION ''Inexistent ID --> %'',user_id; This will abort the transaction with the given error message. PostgreSQL does not have a very smart exception handling model. Whenever the parser, planner/optimizer or executor decide that a statement cannot be processed any longer, the whole transaction gets aborted and the system jumps back into the main loop to get the next query from the client application. It is possible to hook into the error mechanism to notice that this happens. But currently it is impossible to tell what really caused the abort (input/output conversion error, floating-point error, parse error). And it is possible that the database backend is in an inconsistent state at this point so returning to the upper executor or issuing more commands might corrupt the whole database. Thus, the only thing PL/pgSQL currently does when it encounters an abort during execution of a function or trigger procedure is to write some additional NOTICE level log messages telling in which function and where (line number and type of statement) this happened. The error always stops execution of the function. PL/pgSQL can be used to define trigger procedures. A trigger procedure is created with the CREATE FUNCTION command as a function with no arguments and a return type of OPAQUE. Note that the function must be declared with no arguments even if it expects to receive arguments specified in CREATE TRIGGER --- trigger arguments are passed via TG_ARGV, as described below. When a PL/pgSQL function is called as a trigger, several special variables are created automatically in the top-level block. They are: NEW Data type RECORD; variable holding the new database row for INSERT/UPDATE operations in ROW level triggers. OLD Data type RECORD; variable holding the old database row for UPDATE/DELETE operations in ROW level triggers. TG_NAME Data type name; variable that contains the name of the trigger actually fired. TG_WHEN Data type text; a string of either BEFORE or AFTER depending on the trigger's definition. TG_LEVEL Data type text; a string of either ROW or STATEMENT depending on the trigger's definition. TG_OP Data type text; a string of INSERT, UPDATE or DELETE telling for which operation the trigger is fired. TG_RELID Data type oid; the object ID of the table that caused the trigger invocation. TG_RELNAME Data type name; the name of the table that caused the trigger invocation. TG_NARGS Data type integer; the number of arguments given to the trigger procedure in the CREATE TRIGGER statement. TG_ARGV[] Data type array of text; the arguments from the CREATE TRIGGER statement. The index counts from 0 and can be given as an expression. Invalid indices (< 0 or >= tg_nargs) result in a NULL value. A trigger function must return either NULL or a record/row value having exactly the structure of the table the trigger was fired for. Triggers fired BEFORE may return NULL to signal the trigger manager to skip the rest of the operation for this row (ie, subsequent triggers are not fired, and the INSERT/UPDATE/DELETE does not occur for this row). If a non-NULL value is returned then the operation proceeds with that row value. Note that returning a row value different from the original value of NEW alters the row that will be inserted or updated. It is possible to replace single values directly in NEW and return that, or to build a complete new record/row to return. The return value of a trigger fired AFTER is ignored; it may as well always return a NULL value. But an AFTER trigger can still abort the operation by raising an error. This example trigger ensures that any time a row is inserted or updated in the table, the current user name and time are stamped into the row. And it ensures that an employee's name is given and that the salary is a positive value. CREATE TABLE emp ( empname text, salary integer, last_date timestamp, last_user text ); CREATE FUNCTION emp_stamp () RETURNS OPAQUE AS ' BEGIN -- Check that empname and salary are given IF NEW.empname ISNULL THEN RAISE EXCEPTION ''empname cannot be NULL value''; END IF; IF NEW.salary ISNULL THEN RAISE EXCEPTION ''% cannot have NULL salary'', NEW.empname; END IF; -- Who works for us when she must pay for? IF NEW.salary < 0 THEN RAISE EXCEPTION ''% cannot have a negative salary'', NEW.empname; END IF; -- Remember who changed the payroll when NEW.last_date := ''now''; NEW.last_user := current_user; RETURN NEW; END; ' LANGUAGE 'plpgsql'; CREATE TRIGGER emp_stamp BEFORE INSERT OR UPDATE ON emp FOR EACH ROW EXECUTE PROCEDURE emp_stamp(); Here are only a few functions to demonstrate how easy it is to write PL/pgSQL functions. For more complex examples the programmer might look at the regression test for PL/pgSQL. One painful detail in writing functions in PL/pgSQL is the handling of single quotes. The function's source text in CREATE FUNCTION must be a literal string. Single quotes inside of literal strings must be either doubled or quoted with a backslash. We are still looking for an elegant alternative. In the meantime, doubling the single quotes as in the examples below should be used. Any solution for this in future versions of PostgreSQL will be forward compatible. For a detailed explanation and examples of how to escape single quotes in different situations, please see . The following two PL/pgSQL functions are identical to their counterparts from the C language function discussion. This function receives an integer and increments it by one, returning the incremented value. CREATE FUNCTION add_one (integer) RETURNS INTEGER AS ' BEGIN RETURN $1 + 1; END; ' LANGUAGE 'plpgsql'; This function receives two text parameters and returns the result of concatenating them. CREATE FUNCTION concat_text (TEXT, TEXT) RETURNS TEXT AS ' BEGIN RETURN $1 || $2; END; ' LANGUAGE 'plpgsql'; In this example, we take EMP (a table) and an integer as arguments to our function, which returns a boolean. If the salary field of the EMP table is NULL, we return f. Otherwise we compare with that field with the integer passed to the function and return the boolean result of the comparison (t or f). This is the PL/pgSQL equivalent to the example from the C functions. CREATE FUNCTION c_overpaid (EMP, INTEGER) RETURNS BOOLEAN AS ' DECLARE emprec ALIAS FOR $1; sallim ALIAS FOR $2; BEGIN IF emprec.salary ISNULL THEN RETURN ''f''; END IF; RETURN emprec.salary > sallim; END; ' LANGUAGE 'plpgsql'; February 2001 Roberto Mello

rmello@fslc.usu.edu

Oracle PL/SQL Roberto Mello (rmello@fslc.usu.edu) This section explains differences between Oracle's PL/SQL and PostgreSQL's PL/pgSQL languages in the hopes of helping developers port applications from Oracle to PostgreSQL. Most of the code here is from the ArsDigita Clickstream module that I ported to PostgreSQL when I took an internship with OpenForce Inc. in the Summer of 2000. PL/pgSQL is similar to PL/SQL in many aspects. It is a block structured, imperative language (all variables have to be declared). PL/SQL has many more features than its PostgreSQL counterpart, but PL/pgSQL allows for a great deal of functionality and it is being improved constantly. Some things you should keep in mind when porting from Oracle to PostgreSQL: No default parameters in PostgreSQL. You can overload functions in PostgreSQL. This is often used to work around the lack of default parameters. Assignments, loops and conditionals are similar. No need for cursors in PostgreSQL, just put the query in the FOR statement (see example below) In PostgreSQL you need to escape single quotes. See . In PostgreSQL you need to escape single quotes inside your function definition. This can lead to quite amusing code at times, especially if you are creating a function that generates other function(s), as in . One thing to keep in mind when escaping lots of single quotes is that, except for the beginning/ending quotes, all the others will come in even quantity. gives the scoop. (You'll love this little chart.) No. of Quotes Usage Example Result 1 To begin/terminate function bodies CREATE FUNCTION foo() RETURNS INTEGER AS '...' LANGUAGE 'plpgsql'; as is 2 In assignments, SELECTs, to delimit strings, etc. a_output := ''Blah''; SELECT * FROM users WHERE f_name=''foobar''; SELECT * FROM users WHERE f_name='foobar'; 4 When you need two single quotes in your resulting string without terminating that string. a_output := a_output || '' AND name LIKE ''''foobar'''' AND ...'' AND name LIKE 'foobar' AND ... 6 When you want double quotes in your resulting string and terminate that string. a_output := a_output || '' AND name LIKE ''''foobar'''''' AND name LIKE 'foobar' 10 When you want two single quotes in the resulting string (which accounts for 8 quotes) and terminate that string (2 more). You will probably only need that if you were using a function to generate other functions (like in ). a_output := a_output || '' if v_'' || referrer_keys.kind || '' like '''''''''' || referrer_keys.key_string || '''''''''' then return '''''' || referrer_keys.referrer_type || ''''''; end if;''; if v_<...> like ''<...>'' then return ''<...>''; end if; Here is an Oracle function: CREATE OR REPLACE FUNCTION cs_fmt_browser_version(v_name IN varchar, v_version IN varchar) RETURN varchar IS BEGIN IF v_version IS NULL THEN RETURN v_name; END IF; RETURN v_name || '/' || v_version; END; / SHOW ERRORS; Let's go through this function and see the differences to PL/pgSQL: PostgreSQL does not have named parameters. You have to explicitly alias them inside your function. Oracle can have IN, OUT, and INOUT parameters passed to functions. The INOUT, for example, means that the parameter will receive a value and return another. PostgreSQL only has IN parameters and functions can return only a single value. The RETURN key word in the function prototype (not the function body) becomes RETURNS in PostgreSQL. On PostgreSQL functions are created using single quotes as delimiters, so you have to escape single quotes inside your functions (which can be quite annoying at times; see ). The /show errors command does not exist in PostgreSQL. So let's see how this function would look when ported to PostgreSQL: CREATE OR REPLACE FUNCTION cs_fmt_browser_version(VARCHAR, VARCHAR) RETURNS VARCHAR AS ' DECLARE v_name ALIAS FOR $1; v_version ALIAS FOR $2; BEGIN IF v_version IS NULL THEN return v_name; END IF; RETURN v_name || ''/'' || v_version; END; ' LANGUAGE 'plpgsql'; The following procedure grabs rows from a SELECT statement and builds a large function with the results in IF statements, for the sake of efficiency. Notice particularly the differences in cursors, FOR loops, and the need to escape single quotes in PostgreSQL. CREATE OR REPLACE PROCEDURE cs_update_referrer_type_proc IS CURSOR referrer_keys IS SELECT * FROM cs_referrer_keys ORDER BY try_order; a_output VARCHAR(4000); BEGIN a_output := 'CREATE OR REPLACE FUNCTION cs_find_referrer_type(v_host IN VARCHAR, v_domain IN VARCHAR, v_url IN VARCHAR) RETURN VARCHAR IS BEGIN'; FOR referrer_key IN referrer_keys LOOP a_output := a_output || ' IF v_' || referrer_key.kind || ' LIKE ''' || referrer_key.key_string || ''' THEN RETURN ''' || referrer_key.referrer_type || '''; END IF;'; END LOOP; a_output := a_output || ' RETURN NULL; END;'; EXECUTE IMMEDIATE a_output; END; / show errors Here is how this function would end up in PostgreSQL: CREATE FUNCTION cs_update_referrer_type_proc() RETURNS INTEGER AS ' DECLARE referrer_keys RECORD; -- Declare a generic record to be used in a FOR a_output varchar(4000); BEGIN a_output := ''CREATE FUNCTION cs_find_referrer_type(VARCHAR,VARCHAR,VARCHAR) RETURNS VARCHAR AS '''' DECLARE v_host ALIAS FOR $1; v_domain ALIAS FOR $2; v_url ALIAS FOR $3; BEGIN ''; -- -- Notice how we scan through the results of a query in a FOR loop -- using the FOR <record> construct. -- FOR referrer_keys IN SELECT * FROM cs_referrer_keys ORDER BY try_order LOOP a_output := a_output || '' IF v_'' || referrer_keys.kind || '' LIKE '''''''''' || referrer_keys.key_string || '''''''''' THEN RETURN '''''' || referrer_keys.referrer_type || ''''''; END IF;''; END LOOP; a_output := a_output || '' RETURN NULL; END; '''' LANGUAGE ''''plpgsql'''';''; -- This works because we are not substituting any variables -- Otherwise it would fail. Look at PERFORM for another way to run functions EXECUTE a_output; END; ' LANGUAGE 'plpgsql'; The following Oracle PL/SQL procedure is used to parse a URL and return several elements (host, path and query). It is an procedure because in PL/pgSQL functions only one value can be returned (see ). In PostgreSQL, one way to work around this is to split the procedure in three different functions: one to return the host, another for the path and another for the query. CREATE OR REPLACE PROCEDURE cs_parse_url( v_url IN VARCHAR, v_host OUT VARCHAR, -- This will be passed back v_path OUT VARCHAR, -- This one too v_query OUT VARCHAR) -- And this one is a_pos1 INTEGER; a_pos2 INTEGER; begin v_host := NULL; v_path := NULL; v_query := NULL; a_pos1 := instr(v_url, '//'); -- PostgreSQL doesn't have an instr function IF a_pos1 = 0 THEN RETURN; END IF; a_pos2 := instr(v_url, '/', a_pos1 + 2); IF a_pos2 = 0 THEN v_host := substr(v_url, a_pos1 + 2); v_path := '/'; RETURN; END IF; v_host := substr(v_url, a_pos1 + 2, a_pos2 - a_pos1 - 2); a_pos1 := instr(v_url, '?', a_pos2 + 1); IF a_pos1 = 0 THEN v_path := substr(v_url, a_pos2); RETURN; END IF; v_path := substr(v_url, a_pos2, a_pos1 - a_pos2); v_query := substr(v_url, a_pos1 + 1); END; / show errors; Here is how this procedure could be translated for PostgreSQL: CREATE OR REPLACE FUNCTION cs_parse_url_host(VARCHAR) RETURNS VARCHAR AS ' DECLARE v_url ALIAS FOR $1; v_host VARCHAR; v_path VARCHAR; a_pos1 INTEGER; a_pos2 INTEGER; a_pos3 INTEGER; BEGIN v_host := NULL; a_pos1 := instr(v_url,''//''); IF a_pos1 = 0 THEN RETURN ''''; -- Return a blank END IF; a_pos2 := instr(v_url,''/'',a_pos1 + 2); IF a_pos2 = 0 THEN v_host := substr(v_url, a_pos1 + 2); v_path := ''/''; RETURN v_host; END IF; v_host := substr(v_url, a_pos1 + 2, a_pos2 - a_pos1 - 2 ); RETURN v_host; END; ' LANGUAGE 'plpgsql'; PostgreSQL does not have an instr function, so you can work around it using a combination of other functions. I got tired of doing this and created my own instr functions that behave exactly like Oracle's (it makes life easier). See the for the code. Oracle procedures give a little more flexibility to the developer because nothing needs to be explicitly returned, but it can be through the use of INOUT or OUT parameters. An example: CREATE OR REPLACE PROCEDURE cs_create_job(v_job_id IN INTEGER) IS a_running_job_count INTEGER; PRAGMA AUTONOMOUS_TRANSACTION; BEGIN LOCK TABLE cs_jobs IN EXCLUSIVE MODE; SELECT count(*) INTO a_running_job_count FROM cs_jobs WHERE end_stamp IS NULL; IF a_running_job_count > 0 THEN COMMIT; -- free lock raise_application_error(-20000, 'Unable to create a new job: a job is currently running.'); END IF; DELETE FROM cs_active_job; INSERT INTO cs_active_job(job_id) VALUES (v_job_id); BEGIN INSERT INTO cs_jobs (job_id, start_stamp) VALUES (v_job_id, sysdate); EXCEPTION WHEN dup_val_on_index THEN NULL; -- don't worry if it already exists END; COMMIT; END; / show errors Procedures like this can be easily converted into PostgreSQL functions returning an INTEGER. This procedure in particular is interesting because it can teach us some things: There is no pragma statement in PostgreSQL. If you do a LOCK TABLE in PL/pgSQL, the lock will not be released until the calling transaction is finished. You also cannot have transactions in PL/pgSQL procedures. The entire function (and other functions called from therein) is executed in a transaction and PostgreSQL rolls back the results if something goes wrong. Therefore only one BEGIN statement is allowed. The exception when would have to be replaced by an IF statement. So let's see one of the ways we could port this procedure to PL/pgSQL: CREATE OR REPLACE FUNCTION cs_create_job(INTEGER) RETURNS INTEGER AS ' DECLARE v_job_id ALIAS FOR $1; a_running_job_count INTEGER; a_num INTEGER; -- PRAGMA AUTONOMOUS_TRANSACTION; BEGIN LOCK TABLE cs_jobs IN EXCLUSIVE MODE; SELECT count(*) INTO a_running_job_count FROM cs_jobs WHERE end_stamp IS NULL; IF a_running_job_count > 0 THEN -- COMMIT; -- free lock RAISE EXCEPTION ''Unable to create a new job: a job is currently running.''; END IF; DELETE FROM cs_active_job; INSERT INTO cs_active_job(job_id) VALUES (v_job_id); SELECT count(*) into a_num FROM cs_jobs WHERE job_id=v_job_id; IF NOT FOUND THEN -- If nothing was returned in the last query -- This job is not in the table so lets insert it. INSERT INTO cs_jobs(job_id, start_stamp) VALUES (v_job_id, sysdate()); RETURN 1; ELSE RAISE NOTICE ''Job already running.''; END IF; RETURN 0; END; ' LANGUAGE 'plpgsql'; Notice how you can raise notices (or errors) in PL/pgSQL. I haven't done much with packages myself, so if there are mistakes here, please let me know. Packages are a way Oracle gives you to encapsulate PL/SQL statements and functions into one entity, like Java classes, where you define methods and objects. You can access these objects/methods with a . (dot). Here is an example of an Oracle package from ACS 4 (the ArsDigita Community System): CREATE OR REPLACE PACKAGE BODY acs AS FUNCTION add_user ( user_id IN users.user_id%TYPE DEFAULT NULL, object_type IN acs_objects.object_type%TYPE DEFAULT 'user', creation_date IN acs_objects.creation_date%TYPE DEFAULT sysdate, creation_user IN acs_objects.creation_user%TYPE DEFAULT NULL, creation_ip IN acs_objects.creation_ip%TYPE DEFAULT NULL, ... ) RETURN users.user_id%TYPE IS v_user_id users.user_id%TYPE; v_rel_id membership_rels.rel_id%TYPE; BEGIN v_user_id := acs_user.new (user_id, object_type, creation_date, creation_user, creation_ip, email, ... RETURN v_user_id; END; END acs; / show errors We port this to PostgreSQL by creating the different objects of the Oracle package as functions with a standard naming convention. We have to pay attention to some other details, like the lack of default parameters in PostgreSQL functions. The above package would become something like this: CREATE FUNCTION acs__add_user(INTEGER,INTEGER,VARCHAR,DATETIME,INTEGER,INTEGER,...) RETURNS INTEGER AS ' DECLARE user_id ALIAS FOR $1; object_type ALIAS FOR $2; creation_date ALIAS FOR $3; creation_user ALIAS FOR $4; creation_ip ALIAS FOR $5; ... v_user_id users.user_id%TYPE; v_rel_id membership_rels.rel_id%TYPE; BEGIN v_user_id := acs_user__new(user_id,object_type,creation_date,creation_user,creation_ip, ...); ... RETURN v_user_id; END; ' LANGUAGE 'plpgsql'; The PostgreSQL version of EXECUTE works nicely, but you have to remember to use quote_literal(TEXT) and quote_string(TEXT) as described in . Constructs of the type EXECUTE ''SELECT * from $1''; will not work unless you use these functions. PostgreSQL gives you two function creation modifiers to optimize execution: iscachable (function always returns the same result when given the same arguments) and isstrict (function returns NULL if any argument is NULL). Consult the CREATE FUNCTION reference for details. To make use of these optimization attributes, you have to use the WITH modifier in your CREATE FUNCTION statement. Something like: CREATE FUNCTION foo(...) RETURNS INTEGER AS ' ... ' LANGUAGE 'plpgsql' WITH (isstrict, iscachable); This function should probably be integrated into the core. -- -- instr functions that mimic Oracle's counterpart -- Syntax: instr(string1,string2,[n],[m]) where [] denotes optional params. -- -- Searches string1 beginning at the nth character for the mth -- occurrence of string2. If n is negative, search backwards. If m is -- not passed, assume 1 (search starts at first character). -- -- by Roberto Mello (rmello@fslc.usu.edu) -- modified by Robert Gaszewski (graszew@poland.com) -- Licensed under the GPL v2 or later. -- CREATE FUNCTION instr(VARCHAR,VARCHAR) RETURNS INTEGER AS ' DECLARE pos integer; BEGIN pos:= instr($1,$2,1); RETURN pos; END; ' LANGUAGE 'plpgsql'; CREATE FUNCTION instr(VARCHAR,VARCHAR,INTEGER) RETURNS INTEGER AS ' DECLARE string ALIAS FOR $1; string_to_search ALIAS FOR $2; beg_index ALIAS FOR $3; pos integer NOT NULL DEFAULT 0; temp_str VARCHAR; beg INTEGER; length INTEGER; ss_length INTEGER; BEGIN IF beg_index > 0 THEN temp_str := substring(string FROM beg_index); pos := position(string_to_search IN temp_str); IF pos = 0 THEN RETURN 0; ELSE RETURN pos + beg_index - 1; END IF; ELSE ss_length := char_length(string_to_search); length := char_length(string); beg := length + beg_index - ss_length + 2; WHILE beg > 0 LOOP temp_str := substring(string FROM beg FOR ss_length); pos := position(string_to_search IN temp_str); IF pos > 0 THEN RETURN beg; END IF; beg := beg - 1; END LOOP; RETURN 0; END IF; END; ' LANGUAGE 'plpgsql'; -- -- Written by Robert Gaszewski (graszew@poland.com) -- Licensed under the GPL v2 or later. -- CREATE FUNCTION instr(VARCHAR,VARCHAR,INTEGER,INTEGER) RETURNS INTEGER AS ' DECLARE string ALIAS FOR $1; string_to_search ALIAS FOR $2; beg_index ALIAS FOR $3; occur_index ALIAS FOR $4; pos integer NOT NULL DEFAULT 0; occur_number INTEGER NOT NULL DEFAULT 0; temp_str VARCHAR; beg INTEGER; i INTEGER; length INTEGER; ss_length INTEGER; BEGIN IF beg_index > 0 THEN beg := beg_index; temp_str := substring(string FROM beg_index); FOR i IN 1..occur_index LOOP pos := position(string_to_search IN temp_str); IF i = 1 THEN beg := beg + pos - 1; ELSE beg := beg + pos; END IF; temp_str := substring(string FROM beg + 1); END LOOP; IF pos = 0 THEN RETURN 0; ELSE RETURN beg; END IF; ELSE ss_length := char_length(string_to_search); length := char_length(string); beg := length + beg_index - ss_length + 2; WHILE beg > 0 LOOP temp_str := substring(string FROM beg FOR ss_length); pos := position(string_to_search IN temp_str); IF pos > 0 THEN occur_number := occur_number + 1; IF occur_number = occur_index THEN RETURN beg; END IF; END IF; beg := beg - 1; END LOOP; RETURN 0; END IF; END; ' LANGUAGE 'plpgsql';