PL/pgSQL is a loadable procedural language for the Postgres database system. This package was originally written by Jan Wieck. 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. The produced bytecode is identified in the call handler by the object ID of the function. This ensures that changing a function by a DROP/CREATE sequence will take effect without establishing a new database connection. For all expressions and SQL statements used in the function, the PL/pgSQL bytecode interpreter creates a prepared execution plan using the SPI manager's SPI_prepare() and SPI_saveplan() functions. This is done the first time the individual statement is processed in the PL/pgSQL function. Thus, a function with conditional code that contains many statements for which execution plans would be required, will only prepare and save those plans that are really used during the lifetime of the database connection. 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 indices. The PL/pgSQL language is case insensitive. All keywords and identifiers can be used in mixed upper- and lower-case. PL/pgSQL is a block oriented language. A block is defined as <<label>> DECLARE declarations BEGIN statements END; There can be any number of sub-blocks in the statement section of a block. Sub-blocks can be used to hide variables from outside a block 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. 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 Postgres does not have nested transactions. 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 or its sub-blocks must be declared in the declarations section of a block, except for the loop variable of a FOR-loop iterating over a range of integer values. Parameters given to a PL/pgSQL function are automatically declared with the usual identifiers $1, $2, etc. The declarations have the following syntax: name CONSTANT type NOT NULL DEFAULT | := value ; Declares a variable of the specified base type. If the variable is declared as CONSTANT, the value cannot be changed. If NOT NULL is specified, an assignment of a NULL value results in a runtime error. Since the default value of all variables is the SQL NULL value, all variables declared as NOT NULL must also have a default value specified. The default value is evaluated every time the block is entered. So assigning 'now' to a variable of type timestamp causes the variable to have the time of the actual function call, not when the function was precompiled into its bytecode. name table%ROWTYPE; Declares a row with the structure of the given table. table must be an existing table or view name of the database. The fields of the row are accessed in the dot notation. Parameters to a function can be composite types (complete table rows). In that case, the corresponding identifier $n will be a rowtype, but it must be aliased using the ALIAS command described below. Only the user attributes of a table row are accessible in the row, no Oid or other system attributes (because the row could be from a view and view rows don't have useful system attributes). The fields of the rowtype inherit the table's field sizes or precision for char() etc. data types. name RECORD; Records are similar to rowtypes, but they have no predefined structure. They are used in selections and FOR loops to hold one actual database row from a SELECT operation. One and the same record can be used in different selections. Accessing a record or an attempt to assign a value to a record field when there is no actual row in it results in a runtime error. The NEW and OLD rows in a trigger are given to the procedure as records. This is necessary because in Postgres one and the same trigger procedure can handle trigger events for different tables. name ALIAS FOR $n; For better readability of the code it is possible to define an alias for a positional parameter to a function. This aliasing is required for composite types given as arguments to a function. The dot notation $1.salary as in SQL functions is not allowed in PL/pgSQL. RENAME oldname TO newname; Change the name of a variable, record or row. This is useful if NEW or OLD should be referenced by another name inside a trigger procedure. The type of a variable can be any of the existing base types of the database. type in the declarations section above is defined as: Postgres-basetype variable%TYPE table.field%TYPE variable is the name of a variable, previously declared in the same function, that is visible at this point. table is the name of an existing table or view where field is the name of an attribute. Using the table.field%TYPE causes PL/pgSQL to look up the attributes definitions at the first call to the function during the lifetime of a backend. Suppose we have a table with a char(20) attribute and some PL/pgSQL functions that deal with its content in local variables. Now someone decides that char(20) is not enough, dumps the table, drops it, recreates it now with the attribute in question defined as char(40) and restores the data. Hah - he forgot about the functions. The computations inside them will truncate the values to 20 characters. But if they are defined using the table.field%TYPE declarations, they will automagically handle the size change or if the new table schema defines the attribute as text type. All expressions used in PL/pgSQL statements are processed using the backend's executor. Expressions that appear to contain constants may in fact require runtime 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 variable identifiers are substituted by parameters and the actual values from the variables are passed to the executor in the parameter array. All expressions used in a PL/pgSQL function are only prepared and saved once. The only exception to this rule is an EXECUTE statement if parsing of a query is needed each time it is encountered. The type checking done by the Postgres main parser has some side effects to the interpretation of constant values. In detail there is a difference between what the two functions 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'; do. In the case of logfunc1(), the Postgres 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 Postgres main parser does not know what type 'now' should become and therefore it returns a data type of text containing the string 'now'. During the 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. This type checking done by the Postgres main parser got implemented after PL/pgSQL was nearly done. It is a difference between 6.3 and 6.4 and affects all functions using the prepared plan feature of the SPI manager. Using a local variable in the above manner is currently the only way in PL/pgSQL to get those values interpreted correctly. If record fields are used in expressions or statements, the data types of fields should not change between calls of one and the same expression. Keep this in mind when writing trigger procedures that handle events for more than one table. Anything not understood by the PL/pgSQL parser as specified below will be put into a query and sent down to the database engine to execute. The resulting query should not return any data. Assignment An assignment of a value to a variable or row/record field is written as identifier := expression; If the expressions result data type doesn't match the variables data type, or the variable has a size/precision that is known (as for char(20)), the result value will be implicitly cast by the PL/pgSQL bytecode interpreter using the result types output- and the variables type input-functions. Note that this could potentially result in runtime errors generated by the types input functions. An assignment of a complete selection into a record or row can be done by SELECT INTO target expressions FROM ...; target can be a record, a row variable or a comma separated list of variables and record-/row-fields. Note that this is quite different from Postgres' 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 equivalent 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 runtime error occurs. The FROM keyword can be followed by any valid qualification, grouping, sorting etc. that can be given for a SELECT statement. 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. SELECT INTO myrec * FROM EMP WHERE empname = myname; IF NOT FOUND THEN RAISE EXCEPTION ''employee % not found'', myname; END IF; If the selection returns multiple rows, only the first is moved into the target fields. All others are silently discarded. Calling another function All functions defined in a Postgres database return a value. Thus, the normal way to call a function is to execute a SELECT query or doing an assignment (resulting in a PL/pgSQL internal SELECT). But there are cases where someone is not interested in the function's result. PERFORM query executes a SELECT query over the SPI manager and discards the result. Identifiers like local variables are still substituted into parameters. Executing dynamic queries EXECUTE query-string where query-string is a string of type text containing the query to be executed. 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 ... 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. Obtaining other results status 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 datatype 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. Returning from the function RETURN expression The function terminates and the value of expression will be returned to the upper executor. The return value of a function cannot be undefined. If control reaches the end of the top-level block of the function without hitting a RETURN statement, a runtime error will occur. The expressions result will be automatically casted into the function's return type as described for assignments. Aborting and messages As indicated in the above examples there is a RAISE statement that can throw messages into the Postgres elog mechanism. RAISE level 'format' , identifier ...; Inside the format, % is used as a placeholder for the subsequent comma-separated identifiers. Possible levels are DEBUG (silently suppressed in production running databases), NOTICE (written into the database log and forwarded to the client application) and EXCEPTION (written into the database log and aborting the transaction). Conditionals IF expression THEN statements ELSE statements END IF; The expression must return a value that is of type boolean or can be casted to a boolean. Loops There are multiple types of loops. <<label>> LOOP statements END LOOP; An unconditional loop that must be terminated explicitly by an EXIT statement. The optional label can be used by EXIT statements of nested loops to specify which level of nesting should be terminated. <<label>> WHILE expression LOOP statements END LOOP; A conditional loop that is executed as long as the evaluation of expression is true. <<label>> FOR name IN REVERSE expression .. expression LOOP statements END LOOP; A loop that iterates over a range of integer values. The variable name is automatically created as type integer and exists only inside the loop. The two expressions giving the lower and upper bound of the range are evaluated only when entering the loop. The iteration step is always 1. <<label>> FOR record | row IN select_clause LOOP statements END LOOP; The record or row is assigned all the rows resulting from the select clause and the loop body is executed for each row. If the loop is terminated with an EXIT statement, the last assigned row is still accessible after the loop. <<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. EXIT label WHEN expression ; If no label 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 an upper level of nested loop blocks. Then the named loop or block is terminated and control continues with the statement after the loops/blocks corresponding END. PL/pgSQL can be used to define trigger procedures. They are created with the usual CREATE FUNCTION command as a function with no arguments and a return type of OPAQUE. There are some Postgres specific details in functions used as trigger procedures. First they have some special variables created automatically in the top-level blocks declaration section. They are NEW Data type RECORD; variable holding the new database row on INSERT/UPDATE operations on ROW level triggers. OLD Data type RECORD; variable holding the old database row on UPDATE/DELETE operations on 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 triggers definition. TG_LEVEL Data type text; a string of either 'ROW' or 'STATEMENT' depending on the triggers definition. TG_OP Data type text; a string of 'INSERT', 'UPDATE', or 'DELETE' telling for which operation the trigger is actually 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. Second they must return either NULL or a record/row containing exactly the structure of the table the trigger was fired for. Triggers fired AFTER might always return a NULL value with no effect. Triggers fired BEFORE signal the trigger manager to skip the operation for this actual row when returning NULL. Otherwise, the returned record/row replaces the inserted/updated row in the operation. It is possible to replace single values directly in NEW and return that or to build a complete new record/row to return. Postgres 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. And even if, at this point the information, that the transaction is aborted, is already sent to the client application, so resuming operation does not make any sense. 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 DEBUG level log messages telling in which function and where (line number and type of statement) this happened. 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 the CREATE FUNCTION command 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 Postgres will be forward compatible. The following two PL/pgSQL functions are identical to their counterparts from the C language function discussion. CREATE FUNCTION add_one (integer) RETURNS integer AS ' BEGIN RETURN $1 + 1; END; ' LANGUAGE 'plpgsql'; CREATE FUNCTION concat_text (text, text) RETURNS text AS ' BEGIN RETURN $1 || $2; END; ' LANGUAGE 'plpgsql'; Again, 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'; This 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 employees 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(); February 2001 Roberto Mello

rmello@fslc.usu.edu

Except for portions of this document quoted from other sources, this document is licensed under the BSD License. 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: The OR REPLACE clause is not allowed. You will have to explicitly drop the function before creating it to achieve similar results. 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 be look like ported to PostgreSQL: DROP FUNCTION cs_fmt_browser_version(varchar, varchar); CREATE FUNCTION cs_fmt_browser_version(varchar, varchar) RETRUNS 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; ''; -- -- 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 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: drop function cs_parse_url_host(varchar); create 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: drop function cs_create_job(integer); create 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. The third function (that takes 4 parameters) is implemented in PL/Tcl but I plan on porting it to PL/pgSQL so in case we want to include it in OpenACS we don't need to require PL/Tcl. Plus PL/pgSQL should be more efficient. -- -- 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) -- Licensed under the GPL v2 or later. -- DROP FUNCTION instr(varchar, varchar); CREATE FUNCTION instr(varchar, varchar) RETURNS integer AS ' DECLARE pos integer; BEGIN pos:= instr($1, $2, 1); RETURN pos; END; ' LANGUAGE 'plpgsql'; DROP FUNCTION instr(varchar, varchar, integer); 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; ending integer; temp_str varchar; beg integer; length integer; temp_int integer; BEGIN IF beg_index > 0 THEN -- Get substring from 1 to beg_index 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 length := char_length(string); IF beg_index = -1 THEN ending := length; beg := ending; temp_int := 1; ELSE ending := length - abs(beg_index); beg := ending; temp_int := ending - beg; END IF; WHILE pos = 0 AND beg <> 1 LOOP temp_str := substring(string FROM beg FOR temp_int); pos := position(string_to_search IN temp_str); -- Keep moving left beg := beg - 1; temp_int := (ending - beg) + 1; END LOOP; END IF; IF pos = 0 THEN RETURN 0; ELSE RETURN beg + 1; END IF; END; ' LANGUAGE 'plpgsql'; -- -- The next one (where all four params are passed) is in PL/Tcl -- because I had no more patience to do it in PL/pgSQL. -- It'd probably be faster in PL/pgSQL (that being the reason why -- I implemented the first two functions in PL/pgSQL) so someday I'll do it. -- DROP FUNCTION instr(varchar, varchar, integer, integer); CREATE FUNCTION instr(varchar, varchar, integer, integer) RETURNS integer AS ' set string1 $1 set string2 $2 set n $3 set m $4 if { $n > 0 } { set pos [string first $string2 $string1 [expr $n -1]] if { $pos < 0 } { return 0 } else { for { set i 1 } { $i < $m } { incr i } { set pos [string first $string2 $string1 [expr $pos + 1]] if { $pos < 0 } { return 0 } } } } if { $n < 0 } { set pos [string last $string2 $string1 [expr [string length $string1] + $n]] if { $pos < 0 } { return 0 } else { for { set i 1 } { $i < $m } { incr i } { # n is negative so we add set pos [string last $string2 $string1 [expr $pos - 1]] if { $pos < 0 } { return 0 } } } } if { $pos < 0 } { return 0 } else { return [expr $pos + 1] } ' LANGUAGE 'pltcl';