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diff --git a/doc/src/sgml/ref/create_table.sgml b/doc/src/sgml/ref/create_table.sgml deleted file mode 100644 index 5ef7a5d6e70..00000000000 --- a/doc/src/sgml/ref/create_table.sgml +++ /dev/null @@ -1,904 +0,0 @@ -<!-- -$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_table.sgml,v 1.55 2002/05/18 15:44:47 petere Exp $ -PostgreSQL documentation ---> - -<refentry id="SQL-CREATETABLE"> - <refmeta> - <refentrytitle id="sql-createtable-title">CREATE TABLE</refentrytitle> - <refmiscinfo>SQL - Language Statements</refmiscinfo> - </refmeta> - - <refnamediv> - <refname>CREATE TABLE</refname> - <refpurpose>define a new table</refpurpose> - </refnamediv> - - <refsynopsisdiv> -<synopsis> -CREATE [ [ LOCAL ] { TEMPORARY | TEMP } ] TABLE <replaceable class="PARAMETER">table_name</replaceable> ( - { <replaceable class="PARAMETER">column_name</replaceable> <replaceable class="PARAMETER">data_type</replaceable> [ DEFAULT <replaceable>default_expr</> ] [ <replaceable class="PARAMETER">column_constraint</replaceable> [, ... ] ] - | <replaceable>table_constraint</replaceable> } [, ... ] -) -[ INHERITS ( <replaceable>parent_table</replaceable> [, ... ] ) ] -[ WITH OIDS | WITHOUT OIDS ] - -where <replaceable class="PARAMETER">column_constraint</replaceable> is: - -[ CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable> ] -{ NOT NULL | NULL | UNIQUE | PRIMARY KEY | - CHECK (<replaceable class="PARAMETER">expression</replaceable>) | - REFERENCES <replaceable class="PARAMETER">reftable</replaceable> [ ( <replaceable class="PARAMETER">refcolumn</replaceable> ) ] [ MATCH FULL | MATCH PARTIAL ] - [ ON DELETE <replaceable class="parameter">action</replaceable> ] [ ON UPDATE <replaceable class="parameter">action</replaceable> ] } -[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ] - -and <replaceable class="PARAMETER">table_constraint</replaceable> is: - -[ CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable> ] -{ UNIQUE ( <replaceable class="PARAMETER">column_name</replaceable> [, ... ] ) | - PRIMARY KEY ( <replaceable class="PARAMETER">column_name</replaceable> [, ... ] ) | - CHECK ( <replaceable class="PARAMETER">expression</replaceable> ) | - FOREIGN KEY ( <replaceable class="PARAMETER">column_name</replaceable> [, ... ] ) REFERENCES <replaceable class="PARAMETER">reftable</replaceable> [ ( <replaceable class="PARAMETER">refcolumn</replaceable> [, ... ] ) ] - [ MATCH FULL | MATCH PARTIAL ] [ ON DELETE <replaceable class="parameter">action</replaceable> ] [ ON UPDATE <replaceable class="parameter">action</replaceable> ] } -[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ] -</synopsis> - - </refsynopsisdiv> - - <refsect1 id="SQL-CREATETABLE-description"> - <title>Description</title> - - <para> - <command>CREATE TABLE</command> will create a new, initially empty table - in the current database. The table will be owned by the user issuing the - command. - </para> - - <para> - If a schema name is given (for example, <literal>CREATE TABLE - myschema.mytable ...</>) then the table is created in the - specified schema. Otherwise it is created in the current schema (the one - at the front of the search path; see <literal>CURRENT_SCHEMA()</>). - TEMP tables exist in a special schema, so a schema name may not be - given when creating a TEMP table. - The table name must be distinct from the name of any other table, - sequence, index, or view in the same schema. - </para> - - <para> - <command>CREATE TABLE</command> also automatically creates a data - type that represents the tuple type (structure type) corresponding - to one row of the table. Therefore, tables cannot have the same - name as any existing data type in the same schema. - </para> - - <para> - A table cannot have more than 1600 columns. (In practice, the - effective limit is lower because of tuple-length constraints). - </para> - - <para> - The optional constraint clauses specify constraints (or tests) that - new or updated rows must satisfy for an insert or update operation - to succeed. A constraint is a named rule: an SQL object which - helps define valid sets of values by putting limits on the results - of insert, update, or delete operations performed on a table. - </para> - - <para> - There are two ways to define constraints: table constraints and - column constraints. A column constraint is defined as part of a - column definition. A table constraint definition is not tied to a - particular column, and it can encompass more than one column. - Every column constraint can also be written as a table constraint; - a column constraint is only a notational convenience if the - constraint only affects one column. - </para> - </refsect1> - - <refsect1> - <title>Parameters</title> - - <variablelist> - - <varlistentry> - <term><literal>[LOCAL] TEMPORARY</> or <literal>[LOCAL] TEMP</></term> - <listitem> - <para> - If specified, the table is created as a temporary table. - Temporary tables are automatically dropped at the end of a - session. Existing permanent tables with the same name are not - visible to the current session while the temporary table exists, - unless they are referenced with schema-qualified names. - Any indexes created on a temporary table are automatically - temporary as well. - </para> - - <para> - The <literal>LOCAL</literal> word is optional. But see under - <xref linkend="sql-createtable-compatibility" - endterm="sql-createtable-compatibility-title">. - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term><replaceable class="PARAMETER">table_name</replaceable></term> - <listitem> - <para> - The name (optionally schema-qualified) of the table to be created. - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term><replaceable class="PARAMETER">column_name</replaceable></term> - <listitem> - <para> - The name of a column to be created in the new table. - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term><replaceable class="PARAMETER">data_type</replaceable></term> - <listitem> - <para> - The data type of the column. This may include array specifiers. - Refer to the <citetitle>User's Guide</citetitle> for further - information about data types and arrays. - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term><literal>DEFAULT - <replaceable>default_expr</replaceable></literal></term> - <listitem> - <para> - The <literal>DEFAULT</> clause assigns a default data value for - the column whose column definition it appears within. The value - is any variable-free expression (subselects and cross-references - to other columns in the current table are not allowed). The - data type of the default expression must match the data type of the - column. - </para> - - <para> - The default expression will be used in any insert operation that - does not specify a value for the column. If there is no default - for a column, then the default is NULL. - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term><literal>INHERITS ( <replaceable>parent_table</replaceable> [, ... ] )</literal></term> - <listitem> - <para> - The optional <literal>INHERITS</> clause specifies a list of - tables from which the new table automatically inherits all - columns. If the same column name exists in more than one parent - table, an error is reported unless the data types of the columns - match in each of the parent tables. If there is no conflict, - then the duplicate columns are merged to form a single column in - the new table. If the column name list of the new table - contains a column that is also inherited, the data type must - likewise match the inherited column(s), and the column - definitions are merged into one. However, inherited and new - column declarations of the same name need not specify identical - constraints: all constraints provided from any declaration are - merged together and all are applied to the new table. If the - new table explicitly specifies a default value for the column, - this default overrides any defaults from inherited declarations - of the column. Otherwise, any parents that specify default - values for the column must all specify the same default, or an - error will be reported. - </para> -<!-- - <para> - <application>PostgreSQL</application> automatically allows the - created table to inherit - functions on tables above it in the inheritance hierarchy; that - is, if we create table <literal>foo</literal> inheriting from - <literal>bar</literal>, then functions that accept the tuple - type <literal>bar</literal> can also be applied to instances of - <literal>foo</literal>. (Currently, this works reliably for - functions on the first or only parent table, but not so well for - functions on additional parents.) - </para> ---> - </listitem> - </varlistentry> - - <varlistentry> - <term><literal>WITH OIDS</> or <literal>WITHOUT OIDS</></term> - <listitem> - <para> - This optional clause specifies whether rows of the new table - should have OIDs (object identifiers) assigned to them. The - default is to have OIDs. (If the new table inherits from any - tables that have OIDs, then <literal>WITH OIDS</> is forced even - if the command says <literal>WITHOUT OIDS</>.) - </para> - - <para> - Specifying <literal>WITHOUT OIDS</> allows the user to suppress - generation of OIDs for rows of a table. This may be worthwhile - for large tables, since it will reduce OID consumption and - thereby postpone wraparound of the 32-bit OID counter. Once the - counter wraps around, uniqueness of OIDs can no longer be - assumed, which considerably reduces their usefulness. - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term><literal>CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable></literal></term> - <listitem> - <para> - An optional name for a column or table constraint. If not specified, - the system generates a name. - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term><literal>NOT NULL</></term> - <listitem> - <para> - The column is not allowed to contain NULL values. This is - equivalent to the column constraint <literal>CHECK (<replaceable - class="PARAMETER">column</replaceable> NOT NULL)</literal>. - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term><literal>NULL</></term> - <listitem> - <para> - The column is allowed to contain NULL values. This is the default. - </para> - - <para> - This clause is only available for compatibility with - non-standard SQL databases. Its use is discouraged in new - applications. - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term><literal>UNIQUE</> (column constraint)</term> - <term><literal>UNIQUE ( <replaceable class="PARAMETER">column_name</replaceable> [, ... ] )</> (table constraint)</term> - - <listitem> - <para> - The <literal>UNIQUE</literal> constraint specifies a rule that a - group of one or more distinct columns of a table may contain - only unique values. The behavior of the unique table constraint - is the same as that for column constraints, with the additional - capability to span multiple columns. - </para> - - <para> - For the purpose of a unique constraint, NULL values are not - considered equal. - </para> - - <para> - Each unique table constraint must name a set of columns that is - different from the set of columns named by any other unique or - primary key constraint defined for the table. (Otherwise it - would just be the same constraint listed twice.) - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term><literal>PRIMARY KEY</> (column constraint)</term> - <term><literal>PRIMARY KEY ( <replaceable class="PARAMETER">column_name</replaceable> [, ... ] )</> (table constraint)</term> - <listitem> - <para> - The primary key constraint specifies that a column or columns of a table - may contain only unique (non-duplicate), non-NULL values. - Technically, <literal>PRIMARY KEY</literal> is merely a - combination of <literal>UNIQUE</> and <literal>NOT NULL</>, but - identifying a set of columns as primary key also provides - meta-data about the design of the schema, as a primary key - implies that other tables - may rely on this set of columns as a unique identifier for rows. - </para> - - <para> - Only one primary key can be specified for a table, whether as a - column constraint or a table constraint. - </para> - - <para> - The primary key constraint should name a set of columns that is - different from other sets of columns named by any unique - constraint defined for the same table. - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term><literal>CHECK (<replaceable class="PARAMETER">expression</replaceable>)</literal></term> - <listitem> - <para> - <literal>CHECK</> clauses specify integrity constraints or tests - which new or updated rows must satisfy for an insert or update - operation to succeed. Each constraint must be an expression - producing a Boolean result. A condition appearing within a - column definition should reference that column's value only, - while a condition appearing as a table constraint may reference - multiple columns. - </para> - - <para> - Currently, <literal>CHECK</literal> expressions cannot contain - subselects nor refer to variables other than columns of the - current row. - </para> - - </listitem> - </varlistentry> - - - <varlistentry> - <term><literal>REFERENCES <replaceable class="parameter">reftable</replaceable> [ ( <replaceable class="parameter">refcolumn</replaceable> ) ] [ MATCH <replaceable class="parameter">matchtype</replaceable> ] [ ON DELETE <replaceable class="parameter">action</replaceable> ] [ ON UPDATE <replaceable class="parameter">action</replaceable> ]</literal> (column constraint)</term> - - <term><literal>FOREIGN KEY ( <replaceable class="parameter">column</replaceable> [, ... ] ) - REFERENCES <replaceable class="parameter">reftable</replaceable> [ ( <replaceable class="parameter">refcolumn</replaceable> [, ... ] ) ] - [ MATCH <replaceable class="parameter">matchtype</replaceable> ] - [ ON DELETE <replaceable class="parameter">action</replaceable> ] - [ ON UPDATE <replaceable class="parameter">action</replaceable> ]</literal> - (table constraint)</term> - - <listitem> - <para> - The <literal>REFERENCES</literal> column constraint specifies - that a group of one or more columns of the new table must only - contain values which match against values in the referenced - column(s) <replaceable class="parameter">refcolumn</replaceable> - of the referenced table <replaceable - class="parameter">reftable</replaceable>. If <replaceable - class="parameter">refcolumn</replaceable> is omitted, the - primary key of the <replaceable - class="parameter">reftable</replaceable> is used. The - referenced columns must be the columns of a unique or primary - key constraint in the referenced table. - </para> - - <para> - A value added to these columns is matched against the values of - the referenced table and referenced columns using the given - match type. There are three match types: <literal>MATCH - FULL</>, <literal>MATCH PARTIAL</>, and a default match type if - none is specified. <literal>MATCH FULL</> will not allow one - column of a multicolumn foreign key to be NULL unless all - foreign key columns are NULL. The default match type allows some - foreign key columns to be NULL while other parts of the foreign - key are not NULL. <literal>MATCH PARTIAL</> is not yet - implemented. - </para> - - <para> - In addition, when the data in the referenced columns is changed, - certain actions are performed on the data in this table's - columns. The <literal>ON DELETE</literal> clause specifies the - action to do when a referenced row in the referenced table is - being deleted. Likewise, the <literal>ON UPDATE</literal> - clause specifies the action to perform when a referenced column - in the referenced table is being updated to a new value. If the - row is updated, but the referenced column is not actually - changed, no action is done. There are the following possible - actions for each clause: - - <variablelist> - <varlistentry> - <term><literal>NO ACTION</literal></term> - <listitem> - <para> - Produce an error indicating that the deletion or update - would create a foreign key constraint violation. This is - the default action. - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term><literal>RESTRICT</literal></term> - <listitem> - <para> - Same as <literal>NO ACTION</literal>. - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term><literal>CASCADE</literal></term> - <listitem> - <para> - Delete any rows referencing the deleted row, or update the - value of the referencing column to the new value of the - referenced column, respectively. - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term><literal>SET NULL</literal></term> - <listitem> - <para> - Set the referencing column values to NULL. - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term><literal>SET DEFAULT</literal></term> - <listitem> - <para> - Set the referencing column values to their default value. - </para> - </listitem> - </varlistentry> - </variablelist> - </para> - <para> - If primary key column is updated frequently, it may be wise to - add an index to the <literal>REFERENCES</literal> column so that - <literal>NO ACTION</literal> and <literal>CASCADE</literal> - actions associated with the <literal>REFERENCES</literal> - column can be more efficiently performed. - </para> - - </listitem> - </varlistentry> - - <varlistentry> - <term><literal>DEFERRABLE</literal> or <literal>NOT DEFERRABLE</literal></term> - <listitem> - <para> - This controls whether the constraint can be deferred. A - constraint that is not deferrable will be checked immediately - after every command. Checking of constraints that are - deferrable may be postponed until the end of the transaction - (using the <xref linkend="sql-set-constraints" endterm="sql-set-constraints-title"> command). - <literal>NOT DEFERRABLE</literal> is the default. Only foreign - key constraints currently accept this clause. All other - constraint types are not deferrable. - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term><literal>INITIALLY IMMEDIATE</literal> or <literal>INITIALLY DEFERRED</literal></term> - <listitem> - <para> - If a constraint is deferrable, this clause specifies the default - time to check the constraint. If the constraint is - <literal>INITIALLY IMMEDIATE</literal>, it is checked after each - statement. This is the default. If the constraint is - <literal>INITIALLY DEFERRED</literal>, it is checked only at the - end of the transaction. The constraint check time can be - altered with the <xref linkend="sql-set-constraints" endterm="sql-set-constraints-title"> command. - </para> - </listitem> - </varlistentry> - </variablelist> - - - </refsect1> - - - <refsect1 id="SQL-CREATETABLE-diagnostics"> - <title>Diagnostics</title> - - <msgset> - <msgentry> - <msg> - <msgmain> - <msgtext> - <simpara><computeroutput>CREATE TABLE</computeroutput></simpara> - </msgtext> - </msgmain> - </msg> - - <msgexplan> - <para> - Message returned if table is successfully created. - </para> - </msgexplan> - </msgentry> - - - <msgentry> - <msg> - <msgmain> - <msgtext> - <simpara><computeroutput>ERROR</computeroutput></simpara> - </msgtext> - </msgmain> - </msg> - - <msgexplan> - <para> - Message returned if table creation failed. This is usually - accompanied by some descriptive text, such as: - <computeroutput>ERROR: Relation '<replaceable - class="parameter">table</replaceable>' already - exists</computeroutput>, which occurs at run time if the table - specified already exists in the database. - </para> - </msgexplan> - </msgentry> - </msgset> - </refsect1> - - - <refsect1 id="SQL-CREATETABLE-notes"> - <title>Notes</title> - - <itemizedlist> - <listitem> - <para> - Whenever an application makes use of OIDs to identify specific - rows of a table, it is recommended to create a unique constraint - on the <structfield>oid</> column of that table, to ensure that - OIDs in the table will indeed uniquely identify rows even after - counter wraparound. Avoid assuming that OIDs are unique across - tables; if you need a database-wide unique identifier, use the - combination of <structfield>tableoid</> and row OID for the - purpose. (It is likely that future <productname>PostgreSQL</> - releases will use a separate OID counter for each table, so that - it will be <emphasis>necessary</>, not optional, to include - <structfield>tableoid</> to have a unique identifier - database-wide.) - </para> - - <tip> - <para> - The use of <literal>WITHOUT OIDS</literal> is not recommended - for tables with no primary key, since without either an OID or a - unique data key, it is difficult to identify specific rows. - </para> - </tip> - </listitem> - - <listitem> - <para> - <productname>PostgreSQL</productname> automatically creates an - index for each unique constraint and primary key constraint to - enforce the uniqueness. Thus, it is not necessary to create an - explicit index for primary key columns. (See <xref - linkend="sql-createindex" endterm="sql-createindex-title"> for more information.) - </para> - </listitem> - - <listitem> - <para> - The SQL92 standard says that <literal>CHECK</> column constraints - may only refer to the column they apply to; only - <literal>CHECK</> table constraints may refer to multiple - columns. <productname>PostgreSQL</productname> does not enforce - this restriction; it treats column and table check constraints - alike. - </para> - </listitem> - - <listitem> - <para> - Unique constraints and primary keys are not inherited in the - current implementation. This makes the combination of - inheritance and unique constraints rather dysfunctional. - </para> - </listitem> - </itemizedlist> - </refsect1> - - - <refsect1 id="SQL-CREATETABLE-examples"> - <title>Examples</title> - - <para> - Create table <structname>films</> and table - <structname>distributors</>: - -<programlisting> -CREATE TABLE films ( - code CHARACTER(5) CONSTRAINT firstkey PRIMARY KEY, - title CHARACTER VARYING(40) NOT NULL, - did DECIMAL(3) NOT NULL, - date_prod DATE, - kind CHAR(10), - len INTERVAL HOUR TO MINUTE -); -</programlisting> - -<programlisting> -CREATE TABLE distributors ( - did DECIMAL(3) PRIMARY KEY DEFAULT NEXTVAL('serial'), - name VARCHAR(40) NOT NULL CHECK (name <> '') -); -</programlisting> - </para> - - <para> - Create a table with a 2-dimensional array: - -<programlisting> -CREATE TABLE array ( - vector INT[][] -); -</programlisting> - </para> - - <para> - Define a unique table constraint for the table films. Unique table - constraints can be defined on one or more columns of the table: - -<programlisting> -CREATE TABLE films ( - code CHAR(5), - title VARCHAR(40), - did DECIMAL(3), - date_prod DATE, - kind VARCHAR(10), - len INTERVAL HOUR TO MINUTE, - CONSTRAINT production UNIQUE(date_prod) -); -</programlisting> - </para> - - <para> - Define a check column constraint: - -<programlisting> -CREATE TABLE distributors ( - did DECIMAL(3) CHECK (did > 100), - name VARCHAR(40) -); -</programlisting> - </para> - - <para> - Define a check table constraint: - -<programlisting> -CREATE TABLE distributors ( - did DECIMAL(3), - name VARCHAR(40) - CONSTRAINT con1 CHECK (did > 100 AND name <> '') -); -</programlisting> - </para> - - <para> - Define a primary key table constraint for the table - <structname>films</>. Primary key table constraints can be defined - on one or more columns of the table. - -<programlisting> -CREATE TABLE films ( - code CHAR(5), - title VARCHAR(40), - did DECIMAL(3), - date_prod DATE, - kind VARCHAR(10), - len INTERVAL HOUR TO MINUTE, - CONSTRAINT code_title PRIMARY KEY(code,title) -); -</programlisting> - </para> - - <para> - Define a primary key constraint for table - <structname>distributors</>. The following two examples are - equivalent, the first using the table constraint syntax, the second - the column constraint notation. - -<programlisting> -CREATE TABLE distributors ( - did DECIMAL(3), - name CHAR VARYING(40), - PRIMARY KEY(did) -); -</programlisting> - -<programlisting> -CREATE TABLE distributors ( - did DECIMAL(3) PRIMARY KEY, - name VARCHAR(40) -); -</programlisting> - </para> - - <para> - This assigns a literal constant default value for the column - <literal>name</literal>, and arranges for the default value of - column <literal>did</literal> to be generated by selecting the next - value of a sequence object. The default value of - <literal>modtime</literal> will be the time at which the row is - inserted. - -<programlisting> -CREATE TABLE distributors ( - name VARCHAR(40) DEFAULT 'luso films', - did INTEGER DEFAULT NEXTVAL('distributors_serial'), - modtime TIMESTAMP DEFAULT CURRENT_TIMESTAMP -); -</programlisting> - </para> - - <para> - Define two <literal>NOT NULL</> column constraints on the table - <classname>distributors</classname>, one of which is explicitly - given a name: - -<programlisting> -CREATE TABLE distributors ( - did DECIMAL(3) CONSTRAINT no_null NOT NULL, - name VARCHAR(40) NOT NULL -); -</programlisting> - </para> - - <para> - Define a unique constraint for the <literal>name</literal> column: - -<programlisting> -CREATE TABLE distributors ( - did DECIMAL(3), - name VARCHAR(40) UNIQUE -); -</programlisting> - - The above is equivalent to the following specified as a table constraint: - -<programlisting> -CREATE TABLE distributors ( - did DECIMAL(3), - name VARCHAR(40), - UNIQUE(name) -); -</programlisting> - </para> - - </refsect1> - - <refsect1 id="SQL-CREATETABLE-compatibility"> - <title id="SQL-CREATETABLE-compatibility-title">Compatibility</title> - - <para> - The <command>CREATE TABLE</command> conforms to SQL92 Intermediate - and to a subset of SQL99, with exceptions listed below and in the - descriptions above. - </para> - - <refsect2> - <title>Temporary Tables</title> - - <para> - In addition to the local temporary table, SQL92 also defines a - <literal>CREATE GLOBAL TEMPORARY TABLE</literal> statement. - Global temporary tables are also visible to other sessions. - </para> - - <para> - For temporary tables, there is an optional <literal>ON COMMIT</literal> clause: -<synopsis> -CREATE { GLOBAL | LOCAL } TEMPORARY TABLE <replaceable class="parameter">table</replaceable> ( <replaceable class="parameter">...</replaceable> ) [ ON COMMIT { DELETE | PRESERVE } ROWS ] -</synopsis> - - The <literal>ON COMMIT</literal> clause specifies whether or not - the temporary table should be emptied of rows whenever - <command>COMMIT</command> is executed. If the <literal>ON - COMMIT</> clause is omitted, SQL92 specifies that the default is - <literal>ON COMMIT DELETE ROWS</>. However, the behavior of - <productname>PostgreSQL</productname> is always like <literal>ON - COMMIT PRESERVE ROWS</literal>. - </para> - </refsect2> - - <refsect2> - <title><literal>NULL</literal> <quote>Constraint</quote></title> - - <para> - The <literal>NULL</> <quote>constraint</quote> (actually a - non-constraint) is a <productname>PostgreSQL</productname> - extension to SQL92 that is included for compatibility with some - other RDBMS (and for symmetry with the <literal>NOT - NULL</literal> constraint). Since it is the default for any - column, its presence is simply noise. - </para> - </refsect2> - - <refsect2> - <title>Assertions</title> - - <para> - An assertion is a special type of integrity constraint and shares - the same namespace as other constraints. However, an assertion is - not necessarily dependent on one particular table as constraints - are, so SQL92 provides the <command>CREATE ASSERTION</command> - statement as an alternate method for defining a constraint: - -<synopsis> -CREATE ASSERTION <replaceable>name</replaceable> CHECK ( <replaceable>condition</replaceable> ) -</synopsis> - </para> - - <para> - <productname>PostgreSQL</> does not implement assertions at present. - </para> - </refsect2> - -<!-- - <para> - Domain constraints are defined by CREATE DOMAIN or ALTER DOMAIN - statements: - </para> - <para> - Domain constraint: - - <synopsis> -[ CONSTRAINT <replaceable>constraint_name</replaceable> ] CHECK <replaceable>constraint</replaceable> - [ {INITIALLY DEFERRED | INITIALLY IMMEDIATE} ] - [ [ NOT ] DEFERRABLE ] - </synopsis> - </para> ---> - - <refsect2> - <title>Inheritance</title> - - <para> - Multiple inheritance via the <literal>INHERITS</literal> clause is - a <productname>PostgreSQL</productname> language extension. SQL99 - (but not SQL92) defines single inheritance using a different - syntax and different semantics. SQL99-style inheritance is not - yet supported by <productname>PostgreSQL</productname>. - </para> - </refsect2> - - <refsect2> - <title>Object IDs</title> - - <para> - The <productname>PostgreSQL</productname> concept of OIDs is not - standard. - </para> - </refsect2> - </refsect1> - - - <refsect1> - <title>See Also</title> - - <simplelist type="inline"> - <member><xref linkend="sql-altertable"></member> - <member><xref linkend="sql-droptable"></member> - </simplelist> - </refsect1> -</refentry> - -<!-- Keep this comment at the end of the file -Local variables: -mode: sgml -sgml-omittag:nil -sgml-shorttag:t -sgml-minimize-attributes:nil -sgml-always-quote-attributes:t -sgml-indent-step:1 -sgml-indent-data:t -sgml-parent-document:nil -sgml-default-dtd-file:"../reference.ced" -sgml-exposed-tags:nil -sgml-local-catalogs:"/usr/lib/sgml/catalog" -sgml-local-ecat-files:nil -End: ---> |