<!--
-$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_table.sgml,v 1.39 2001/01/05 06:34:16 tgl Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_table.sgml,v 1.40 2001/01/12 05:06:40 tgl Exp $
Postgres documentation
-->
</refnamediv>
<refsynopsisdiv>
<refsynopsisdivinfo>
- <date>2001-01-04</date>
+ <date>2001-01-11</date>
</refsynopsisdivinfo>
<synopsis>
-CREATE [ TEMPORARY | TEMP ] TABLE <replaceable class="PARAMETER">table</replaceable> (
- <replaceable class="PARAMETER">column</replaceable> <replaceable class="PARAMETER">type</replaceable>
- [ NULL | NOT NULL ] [ UNIQUE ] [ DEFAULT <replaceable class="PARAMETER">value</replaceable> ]
- [<replaceable>column_constraint_clause</replaceable> | PRIMARY KEY } [ ... ] ]
- [, ... ]
- [, PRIMARY KEY ( <replaceable class="PARAMETER">column</replaceable> [, ...] ) ]
- [, CHECK ( <replaceable class="PARAMETER">condition</replaceable> ) ]
- [, <replaceable>table_constraint_clause</replaceable> ]
- ) [ INHERITS ( <replaceable>inherited_table</replaceable> [, ...] ) ]
+CREATE [ TEMPORARY | TEMP ] TABLE <replaceable class="PARAMETER">table_name</replaceable> (
+ { <replaceable class="PARAMETER">column_name</replaceable> <replaceable class="PARAMETER">type</replaceable> [ <replaceable class="PARAMETER">column_constraint</replaceable> [ ... ] ]
+ | <replaceable>table_constraint</replaceable> } [, ... ]
+ ) [ INHERITS ( <replaceable>inherited_table</replaceable> [, ... ] ) ]
+
+where <replaceable class="PARAMETER">column_constraint</replaceable> can be:
+[ CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable> ]
+{ NOT NULL | NULL | UNIQUE | PRIMARY KEY | DEFAULT <replaceable class="PARAMETER">value</replaceable> | CHECK (<replaceable class="PARAMETER">condition</replaceable>) |
+ REFERENCES <replaceable class="PARAMETER">table</replaceable> [ ( <replaceable class="PARAMETER">column</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> can be:
+[ 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">condition</replaceable> ) |
+ FOREIGN KEY ( <replaceable class="PARAMETER">column_name</replaceable> [, ... ] ) REFERENCES <replaceable class="PARAMETER">table</replaceable> [ ( <replaceable class="PARAMETER">column</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>
<refsect2 id="R2-SQL-CREATETABLE-1">
<variablelist>
<varlistentry>
- <term>TEMPORARY</term>
+ <term>TEMPORARY or TEMP</term>
<listitem>
<para>
- The table is created only for this session, and is
+ If specified, the table is created only for this session, and is
automatically dropped on session exit.
Existing permanent tables with the same name are not visible
- while the temporary table exists.
+ (in this session) while the temporary table exists.
+ Any indexes created on a temporary table are automatically
+ temporary as well.
</para>
</listitem>
</varlistentry>
<varlistentry>
- <term><replaceable class="PARAMETER">table</replaceable></term>
+ <term><replaceable class="PARAMETER">table_name</replaceable></term>
<listitem>
<para>
The name of the new table to be created.
</varlistentry>
<varlistentry>
- <term><replaceable class="PARAMETER">column</replaceable></term>
+ <term><replaceable class="PARAMETER">column_name</replaceable></term>
<listitem>
<para>
- The name of a column.
+ The name of a column to be created in the new table.
</para>
</listitem>
</varlistentry>
</varlistentry>
<varlistentry>
- <term>DEFAULT <replaceable class="PARAMETER">value</replaceable></term>
+ <term><replaceable class="PARAMETER">inherited_table</replaceable></term>
+ <listitem>
+ <para>
+ The optional INHERITS clause specifies a list of table
+ names from which this table automatically inherits all fields.
+ If any inherited field name appears more than once,
+ <productname>Postgres</productname>
+ reports an error.
+ <productname>Postgres</productname> automatically allows the created
+ table to inherit functions on tables above it in the inheritance
+ hierarchy.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><replaceable class="PARAMETER">constraint_name</replaceable></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><replaceable class="PARAMETER">value</replaceable></term>
<listitem>
<para>
A default value for a column.
</varlistentry>
<varlistentry>
- <term><replaceable>column_constraint_clause</replaceable></term>
+ <term><replaceable class="PARAMETER">condition</replaceable></term>
<listitem>
<para>
- The optional column constraint clauses specify a list of
- integrity constraints or tests which new or updated entries must
- satisfy for an insert or update operation to succeed. Each
- constraint must evaluate to a boolean expression. Although
- <acronym>SQL92</acronym> requires the <replaceable
- class="PARAMETER">column_constraint_clause</replaceable> to
- refer to that column only, <productname>Postgres</productname>
- allows multiple columns to be referenced within a single column
- constraint. See the column constraint clause for more
- information.
+ 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>
</listitem>
</varlistentry>
<varlistentry>
- <term><replaceable>table_constraint_clause</replaceable></term>
+ <term><replaceable class="PARAMETER">table</replaceable></term>
<listitem>
<para>
- The optional table CONSTRAINT clause specifies a
- list of integrity constraints which new or updated entries must
- satisfy for an insert or update operation to succeed. Each
- constraint must evaluate to a boolean expression. Multiple
- columns may be referenced within a single constraint. Only one
- PRIMARY KEY clause may be specified for a table;
- PRIMARY KEY <replaceable>column</replaceable> (a table
- constraint) and PRIMARY KEY (a column constraint)
- are mutually exclusive. See the table constraint clause for
- more information.
+ The name of an existing table to be referenced by a foreign
+ key constraint.
</para>
</listitem>
</varlistentry>
<varlistentry>
- <term>INHERITS <replaceable class="PARAMETER">inherited_table</replaceable></term>
+ <term><replaceable class="PARAMETER">column</replaceable></term>
<listitem>
<para>
- The optional INHERITS clause specifies a list of table
- names from which this table automatically inherits all fields.
- If any inherited field name appears more than once,
- <productname>Postgres</productname>
- reports an error.
- <productname>Postgres</productname> automatically allows the created
- table to inherit functions on tables above it in the inheritance
- hierarchy.
+ The name of a column in an existing table to be referenced by a
+ foreign key constraint. If not specified, the primary key of
+ the existing table is assumed.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><replaceable class="PARAMETER">action</replaceable></term>
+ <listitem>
+ <para>
+ A keyword indicating the action to take when a foreign key
+ constraint is violated.
</para>
</listitem>
</varlistentry>
</para>
</listitem>
</varlistentry>
-
- <varlistentry>
- <term><computeroutput>
-ERROR: DEFAULT: type mismatched
- </computeroutput></term>
- <listitem>
- <para>
- If data type of default value doesn't match the
- column definition's data type.
- </para>
- </listitem>
- </varlistentry>
</variablelist>
</para>
</refsect2>
</title>
<para>
- <command>CREATE TABLE</command> will enter a new table
- into the current data base. The table will be "owned" by the user issuing the
+ <command>CREATE TABLE</command> will enter a new, initially empty table
+ into the current database. The table will be "owned" by the user issuing the
command.
</para>
</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 can't have the same name as any
+ existing datatype.
+ </para>
+
+ <para>
The optional INHERITS
clause specifies a collection of table names from which this table
automatically inherits all fields. If any inherited field name
</para>
<para>
- Each new table <replaceable class="PARAMETER">table</replaceable>
- is automatically created as a type. Therefore, one or more rows
- from the table are automatically a type and can be used in
- <xref linkend="sql-altertable" endterm="sql-altertable-title">
- or other <command>CREATE TABLE</command> statements.
- </para>
-
- <para>
- The new table is created as a heap with no initial data.
A table can have no more than 1600 columns (in practice, the
effective limit is lower because of tuple-length constraints).
A table cannot have the same name as a system catalog table.
DEFAULT <replaceable class="PARAMETER">value</replaceable>
</synopsis>
</para>
- <refsect2 id="R2-SQL-DEFAULTCLAUSE-1">
- <title>
- Inputs
- </title>
- <para>
- <variablelist>
- <varlistentry>
- <term><replaceable class="parameter">value</replaceable></term>
- <listitem>
- <para>
- The possible values for the default value expression are:
- <itemizedlist>
- <listitem>
- <simpara>
- a literal value
- </simpara>
- </listitem>
- <listitem>
- <simpara>
- a user function
- </simpara>
- </listitem>
- <listitem>
- <simpara>
- a niladic function
- </simpara>
- </listitem>
- </itemizedlist>
- </para>
- </listitem>
- </varlistentry>
- </variablelist>
- </para>
- </refsect2>
+ <para>
+ The DEFAULT clause assigns a default data value for the column whose
+ column definition it appears within. The value is any variable-free
+ expression (note that sub-selects and cross-references to other
+ columns in the current table are not supported).
+ The data type of a default value must match the column definition's
+ data type.
+ </para>
- <refsect2 id="R2-SQL-DEFAULTCLAUSE-2">
- <title>
- Outputs
- </title>
- <para>
- None.
- </para>
- </refsect2>
-
- <refsect2 id="R2-SQL-DEFAULTCLAUSE-3">
- <title>
- Description
- </title>
- <para>
- The DEFAULT clause assigns a default data value to a column
- (via a column definition in the CREATE TABLE statement).
- The data type of a default value must match the column definition's
- data type.
- </para>
- <para>
- An INSERT operation that includes a column without a specified
- default value will assign the NULL value to the column
- if no explicit data value is provided for it.
- Default <replaceable class="parameter">literal</replaceable> means
- that the default is the specified constant value.
- Default <replaceable class="parameter">niladic-function</replaceable>
- or <replaceable class="parameter">user-function</replaceable> means
- that the default
- is the value of the specified function at the time of the INSERT.
- </para>
- <para>
- There are two types of niladic functions:
- <variablelist>
- <varlistentry>
- <term>niladic USER</term>
- <listitem>
- <variablelist>
- <varlistentry>
- <term>CURRENT_USER / USER</term>
- <listitem>
- <simpara>See CURRENT_USER function</simpara>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term>SESSION_USER</term>
- <listitem>
- <simpara>See CURRENT_USER function</simpara>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term>SYSTEM_USER</term>
- <listitem>
- <simpara>Not implemented</simpara>
- </listitem>
- </varlistentry>
- </variablelist>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term>niladic datetime</term>
- <listitem>
- <variablelist>
- <varlistentry>
- <term>CURRENT_DATE</term>
- <listitem>
- <simpara>See CURRENT_DATE function</simpara>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term>CURRENT_TIME</term>
- <listitem>
- <simpara>See CURRENT_TIME function</simpara>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term>CURRENT_TIMESTAMP</term>
- <listitem>
- <simpara>See CURRENT_TIMESTAMP function</simpara>
- </listitem>
- </varlistentry>
- </variablelist>
- </listitem>
- </varlistentry>
- </variablelist>
- </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 clause,
+ then the default is NULL.
+ </para>
- </refsect2>
- <refsect2 id="R2-SQL-DEFAULTCLAUSE-4">
+ <refsect2 id="R2-SQL-DEFAULTCLAUSE-2">
<title>
Usage
</title>
<para>
- To assign a constant value as the default for the
- columns <literal>did</literal> and <literal>number</literal>,
- and a string literal to the column <literal>did</literal>:
-
<programlisting>
-CREATE TABLE video_sales (
- did VARCHAR(40) DEFAULT 'luso films',
- number INTEGER DEFAULT 0,
- total CASH DEFAULT '$0.0'
+CREATE TABLE distributors (
+ name VARCHAR(40) DEFAULT 'luso films',
+ did INTEGER DEFAULT NEXTVAL('distributors_serial'),
+ modtime TIMESTAMP DEFAULT now()
);
</programlisting>
+ The above 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.
</para>
- <para>
- To assign an existing sequence
- as the default for the column <literal>did</literal>,
- and a literal to the column <literal>name</literal>:
+ <para>
+ It is worth remarking that
<programlisting>
-CREATE TABLE distributors (
- did DECIMAL(3) DEFAULT NEXTVAL('serial'),
- name VARCHAR(40) DEFAULT 'luso films'
-);
+ modtime TIMESTAMP DEFAULT 'now'
</programlisting>
+ would produce a result that is probably not the intended one: the
+ string <literal>'now'</literal> will be coerced to a timestamp value
+ immediately, and so the default value of <literal>modtime</literal> will
+ always be the time of table creation. This difficulty is avoided by
+ specifying the default value as a function call.
</para>
</refsect2>
</refsect1>
<refsect1 id="R1-SQL-COLUMNCONSTRAINT-1">
<title id="R1-SQL-COLUMNCONSTRAINT-1-TITLE">
- Column CONSTRAINT Clause
+ Column Constraints
</title>
<para>
<synopsis>
-[ CONSTRAINT <replaceable class="parameter">name</replaceable> ] { [
- NULL | NOT NULL ] | UNIQUE | PRIMARY KEY | CHECK <replaceable
- class="parameter">constraint</replaceable> | REFERENCES
- <replaceable class="parameter">reftable</replaceable>
- (<replaceable class="parameter">refcolumn</replaceable>)
+[ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ] {
+ NULL | NOT NULL | UNIQUE | PRIMARY KEY | CHECK <replaceable
+ class="parameter">condition</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> ]
[ [ NOT ] DEFERRABLE ]
[ INITIALLY <replaceable class="parameter">checktime</replaceable> ] }
- [, ...]
</synopsis>
</para>
<variablelist>
<varlistentry>
- <term><replaceable class="parameter">name</replaceable></term>
+ <term><replaceable class="parameter">constraint_name</replaceable></term>
<listitem>
<para>
- An arbitrary name given to the integrity constraint.
- If <replaceable class="parameter">name</replaceable> is not specified,
- it is generated from the table and column names,
- which should ensure uniqueness for
- <replaceable class="parameter">name</replaceable>.
+ An arbitrary name given to a constraint clause.
</para>
</listitem>
</varlistentry>
<listitem>
<para>
The column must have unique values. In <productname>Postgres</productname>
- this is enforced by an implicit creation of a unique index on the table.
+ this is enforced by automatic creation of a unique index on the column.
</para>
</listitem>
</varlistentry>
<term>PRIMARY KEY</term>
<listitem>
<para>
- This column is a primary key, which implies that uniqueness is
- enforced by the system and that other tables may rely on this
- column as a unique identifier for rows. See PRIMARY KEY for more
+ This column is a primary key, which implies that other tables may rely
+ on this column as a unique identifier for rows. Both UNIQUE and
+ NOT NULL are implied by PRIMARY KEY. See PRIMARY KEY for more
information.
</para>
</listitem>
<varlistentry>
<term>
-<replaceable class="parameter">constraint</replaceable>
+<replaceable class="parameter">condition</replaceable>
</term>
<listitem>
<para>
- The definition of the constraint.
+ An arbitrary boolean-valued constraint condition.
</para>
</listitem>
</varlistentry>
<para>
The optional constraint clauses specify constraints or tests which
- new or updated entries must satisfy for an insert or update
- operation to succeed. Each constraint must evaluate to a boolean
- expression. Multiple attributes may be referenced within a single
- constraint. The use of PRIMARY KEY as a table constraint is mutually
- incompatible with PRIMARY KEY as a column constraint.
+ new or updated rows must satisfy for an insert or update
+ operation to succeed.
</para>
<para>
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 Base Table.
+ UPDATE or DELETE operations performed on a table.
</para>
<para>
<para>
Define two NOT NULL column constraints on the table
<classname>distributors</classname>,
- one of which being a named constraint:
+ one of which is explicitly given a name:
<programlisting>
CREATE TABLE distributors (
UNIQUE Constraint
</title>
<synopsis>
-[ CONSTRAINT <replaceable class="parameter">name</replaceable> ] UNIQUE
+[ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ] UNIQUE
</synopsis>
<refsect3>
<variablelist>
<varlistentry>
- <term>CONSTRAINT <replaceable class="parameter">name</replaceable></term>
+ <term><replaceable class="parameter">constraint_name</replaceable></term>
<listitem>
<para>
- An arbitrary label given to a constraint.
+ An arbitrary name given to a constraint clause.
</para>
</listitem>
</varlistentry>
</title>
<para>
- Defines a UNIQUE column constraint for the table distributors.
- UNIQUE column constraints can only be defined on one column
- of the table:
+ Defines a UNIQUE constraint for the <literal>name</literal> column:
<programlisting>
CREATE TABLE distributors (
did DECIMAL(3),
The CHECK Constraint
</title>
<synopsis>
-[ CONSTRAINT <replaceable class="parameter">name</replaceable> ] CHECK
- ( <replaceable>condition</replaceable> [, ...] )
+[ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ] CHECK ( <replaceable>condition</replaceable> )
</synopsis>
<refsect3 id="R3-SQL-CHECK-1">
<title>Inputs</title>
<variablelist>
<varlistentry>
- <term><replaceable class="parameter">name</replaceable></term>
+ <term><replaceable class="parameter">constraint_name</replaceable></term>
<listitem>
<para>
- An arbitrary name given to a constraint.
+ An arbitrary name given to a constraint clause.
</para>
</listitem>
</varlistentry>
<variablelist>
<varlistentry>
<term><computeroutput>
-ERROR: ExecAppend: rejected due to CHECK constraint "<replaceable class="parameter">table_column</replaceable>".
+ERROR: ExecAppend: rejected due to CHECK constraint "<replaceable class="parameter">constraint_name</replaceable>".
</computeroutput></term>
<listitem>
<para>
<refsect3>
<title>Description</title>
<para>
- The CHECK constraint specifies a restriction on allowed values
+ The CHECK constraint specifies a generic restriction on allowed values
within a column. The CHECK constraint is also allowed as a table
constraint.
</para>
<para>
- The SQL92 CHECK column constraints can only be defined on, and
- refer to, one column of the table.
- <productname>Postgres</productname> does not have this restriction.
+ CHECK specifies a general boolean expression involving one or more
+ columns of a table. A new row will be rejected if the boolean
+ expression evaluates to FALSE when applied to the row's values.
+ </para>
+ <para>
+ Currently, CHECK expressions cannot contain sub-selects nor refer
+ to variables other than fields of the current row.
+ </para>
+ <para>
+ The SQL92 standard says that CHECK column constraints may only refer
+ to the column they apply to; only CHECK table constraints may refer
+ to multiple columns.
+ <productname>Postgres</productname> does not enforce this restriction.
+ It treats column and table CHECK constraints alike.
</para>
</refsect3>
</refsect2>
PRIMARY KEY Constraint
</title>
<synopsis>
-[ CONSTRAINT <replaceable class="PARAMETER">name</replaceable> ] PRIMARY KEY
+[ CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable> ] PRIMARY KEY
</synopsis>
<refsect3>
<para>
<variablelist>
<varlistentry>
- <term>CONSTRAINT <replaceable class="PARAMETER">name</replaceable></term>
+ <term><replaceable class="PARAMETER">constraint_name</replaceable></term>
<listitem>
<para>
- An arbitrary name for the constraint.
+ An arbitrary name given to a constraint clause.
</para>
</listitem>
</varlistentry>
constraint.
</para>
<para>
- Only one PRIMARY KEY can be specified for a table.
+ Only one PRIMARY KEY can be specified for a table, whether as a
+ column constraint or a table constraint.
</para>
</refsect3>
REFERENCES Constraint
</title>
<synopsis>
-[ CONSTRAINT <replaceable class="parameter">name</replaceable> ] REFERENCES <replaceable class="parameter">reftable</replaceable> [ ( <replaceable class="parameter">refcolumn</replaceable> ) ]
+[ CONSTRAINT <replaceable class="parameter">constraint_name</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> ]
<para>
<variablelist>
<varlistentry>
- <term>CONSTRAINT <replaceable class="PARAMETER">name</replaceable></term>
+ <term><replaceable class="PARAMETER">constraint_name</replaceable></term>
<listitem>
<para>
- An arbitrary name for the constraint.
+ An arbitrary name given to a constraint clause.
</para>
</listitem>
</varlistentry>
default match type if none is specified. MATCH FULL will not
allow one column of a multi-column foreign key to be NULL
unless all foreign key columns are NULL. The default MATCH type
- allows a some foreign key columns to be NULL while other parts
+ allows some foreign key columns to be NULL while other parts
of the foreign key are not NULL. MATCH PARTIAL is currently not
supported.
</para>
<refsect1 id="R1-SQL-TABLECONSTRAINT-1">
<title>
- Table CONSTRAINT Clause
+ Table Constraints
</title>
<para>
<synopsis>
-[ CONSTRAINT name ] { PRIMARY KEY | UNIQUE } ( <replaceable class="parameter">column</replaceable> [, ...] )
+[ CONSTRAINT name ] { PRIMARY KEY | UNIQUE } ( <replaceable class="parameter">column</replaceable> [, ... ] )
[ CONSTRAINT name ] CHECK ( <replaceable>constraint</replaceable> )
-[ CONSTRAINT name ] FOREIGN KEY ( <replaceable class="parameter">column</replaceable> [, ...] )
- REFERENCES <replaceable class="parameter">reftable</replaceable>
- (<replaceable class="parameter">refcolumn</replaceable> [, ...] )
+[ CONSTRAINT name ] 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> ]
<variablelist>
<varlistentry>
- <term>CONSTRAINT <replaceable class="parameter">name</replaceable></term>
+ <term><replaceable class="parameter">constraint_name</replaceable></term>
<listitem>
<para>
- An arbitrary name given to an integrity constraint.
+ An arbitrary name given to a constraint clause.
</para>
</listitem>
</varlistentry>
<varlistentry>
- <term><replaceable class="parameter">column</replaceable> [, ...]</term>
+ <term><replaceable class="parameter">column</replaceable> [, ... ]</term>
<listitem>
<para>
The column name(s) for which to define a unique index
<para>
A table constraint is an integrity constraint defined on one or
- more columns of a base table. The four variations of "Table
+ more columns of a table. The four variations of "Table
Constraint" are:
<simplelist columns="1">
<member>UNIQUE</member>
</title>
<para>
<synopsis>
-[ CONSTRAINT <replaceable class="parameter">name</replaceable> ] UNIQUE ( <replaceable class="parameter">column</replaceable> [, ...] )
+[ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ] UNIQUE ( <replaceable class="parameter">column</replaceable> [, ... ] )
</synopsis>
</para>
<refsect3>
<title>Inputs</title>
<variablelist>
<varlistentry>
- <term>CONSTRAINT <replaceable class="parameter">name</replaceable></term>
+ <term><replaceable class="parameter">constraint_name</replaceable></term>
<listitem>
<para>
- An arbitrary name given to a constraint.
+ An arbitrary name given to a constraint clause.
</para>
</listitem>
</varlistentry>
</title>
<para>
- Define a UNIQUE table constraint for the table distributors:
+ Prevent duplicate rows in the table distributors:
<programlisting>
CREATE TABLE distributors (
did DECIMAL(3),
name VARCHAR(40),
- UNIQUE(name)
+ UNIQUE(did,name)
);
</programlisting>
</para>
</title>
<para>
<synopsis>
-[ CONSTRAINT <replaceable class="PARAMETER">name</replaceable> ] PRIMARY KEY ( <replaceable class="PARAMETER">column</replaceable> [, ...] )
+[ CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable> ] PRIMARY KEY ( <replaceable class="PARAMETER">column</replaceable> [, ... ] )
</synopsis>
</para>
<refsect3>
<variablelist>
<varlistentry>
- <term>CONSTRAINT <replaceable class="PARAMETER">name</replaceable></term>
+ <term><replaceable class="PARAMETER">constraint_name</replaceable></term>
<listitem>
<para>
- An arbitrary name for the constraint.
+ An arbitrary name given to a constraint clause.
</para>
</listitem>
</varlistentry>
<varlistentry>
- <term><replaceable class="PARAMETER">column</replaceable> [, ...]</term>
+ <term><replaceable class="PARAMETER">column</replaceable> [, ... ]</term>
<listitem>
<para>
The names of one or more columns in the table.
REFERENCES Constraint
</title>
<synopsis>
-[ CONSTRAINT <replaceable class="parameter">name</replaceable> ] FOREIGN KEY ( <replaceable class="parameter">column</replaceable> [, ...] )
- REFERENCES <replaceable class="parameter">reftable</replaceable> [ ( <replaceable class="parameter">refcolumn</replaceable> [, ...] ) ]
+[ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ] 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> ]
[ INITIALLY <replaceable class="parameter">checktime</replaceable> ]
</synopsis>
<para>
- The REFERENCES constraint specifies a rule that a column value is
- checked against the values of another column. REFERENCES can also be
- specified as part of a FOREIGN KEY table constraint.
+ The REFERENCES constraint specifies a rule that a column value or set
+ of column values is
+ checked against the values in another table.
</para>
<refsect3 id="R3-SQL-REFERENCES-5">
<para>
<variablelist>
<varlistentry>
- <term>CONSTRAINT <replaceable class="PARAMETER">name</replaceable></term>
+ <term><replaceable class="PARAMETER">constraint_name</replaceable></term>
<listitem>
<para>
- An arbitrary name for the constraint.
+ An arbitrary name given to a constraint clause.
</para>
</listitem>
</varlistentry>
<varlistentry>
- <term><replaceable class="PARAMETER">column</replaceable> [, ...]</term>
+ <term><replaceable class="PARAMETER">column</replaceable> [, ... ]</term>
<listitem>
<para>
The names of one or more columns in the table.
</listitem>
</varlistentry>
<varlistentry>
- <term><replaceable class="parameter">referenced column</replaceable> [, ...]</term>
+ <term><replaceable class="parameter">referenced column</replaceable> [, ... ]</term>
<listitem>
<para>
- One or more column in the <replaceable class="parameter">reftable</replaceable>
+ One or more columns in the <replaceable class="parameter">reftable</replaceable>
to check the data against. If this is not specified, the PRIMARY KEY of the
<replaceable class="parameter">reftable</replaceable> is used.
</para>
ON COMMIT clause:
<synopsis>
CREATE GLOBAL TEMPORARY TABLE <replaceable class="parameter">table</replaceable> ( <replaceable class="parameter">column</replaceable> <replaceable class="parameter">type</replaceable> [
- DEFAULT <replaceable class="parameter">value</replaceable> ] [ CONSTRAINT <replaceable class="parameter">column_constraint</replaceable> ] [, ...] )
+ DEFAULT <replaceable class="parameter">value</replaceable> ] [ CONSTRAINT <replaceable class="parameter">column_constraint</replaceable> ] [, ... ] )
[ CONSTRAINT <replaceable class="parameter">table_constraint</replaceable> ] [ ON COMMIT { DELETE | PRESERVE } ROWS ]
</synopsis>
</para>
<para>
For temporary tables, the CREATE GLOBAL TEMPORARY TABLE statement
- names a new table visible to other clients and defines the table's columns and
- constraints.
+ names a new table visible to other clients and defines the table's columns
+ and constraints.
</para>
<para>
The optional ON COMMIT clause of CREATE TEMPORARY TABLE specifies
whether or not the temporary table should be emptied of rows
- whenever COMMIT is executed. If the ON COMMIT clause is omitted, the
- default option, ON COMMIT DELETE ROWS, is assumed.
- </para>
- <para>
- To create a temporary table:
-
- <programlisting>
-CREATE TEMPORARY TABLE actors (
- id DECIMAL(3),
- name VARCHAR(40),
- CONSTRAINT actor_id CHECK (id < 150)
-) ON COMMIT DELETE ROWS;
- </programlisting>
+ whenever COMMIT is executed. If the ON COMMIT clause is omitted, SQL92
+ specifies that the default is ON COMMIT DELETE ROWS. However,
+ <productname>Postgres</productname>' behavior is always like
+ ON COMMIT PRESERVE ROWS.
</para>
<refsect3 id="R3-SQL-UNIQUECLAUSE-1">
Table Constraint definition:
<synopsis>
-[ CONSTRAINT <replaceable>name</replaceable> ] UNIQUE ( <replaceable>column</replaceable> [, ...] )
+[ CONSTRAINT <replaceable>constraint_name</replaceable> ] UNIQUE ( <replaceable>column</replaceable> [, ... ] )
[ { INITIALLY DEFERRED | INITIALLY IMMEDIATE } ]
[ [ NOT ] DEFERRABLE ]
</synopsis>
Column Constraint definition:
<synopsis>
-[ CONSTRAINT <replaceable>name</replaceable> ] UNIQUE
+[ CONSTRAINT <replaceable>constraint_name</replaceable> ] UNIQUE
[ {INITIALLY DEFERRED | INITIALLY IMMEDIATE} ]
[ [ NOT ] DEFERRABLE ]
</synopsis>
</title>
<para>
The NULL "constraint" (actually a non-constraint) is a
- <productname>Postgres</productname> extension to SQL92 is
- included for symmetry with the NOT NULL clause. Since it is the
+ <productname>Postgres</productname> extension to SQL92 that is
+ included for symmetry with the NOT NULL clause (and for compatibility
+ with some other RDBMSes). Since it is the
default for any column, its presence is simply noise.
<synopsis>
-[ CONSTRAINT <replaceable>name</replaceable> ] NULL
+[ CONSTRAINT <replaceable>constraint_name</replaceable> ] NULL
</synopsis>
</para>
</refsect3>
SQL92 specifies some additional capabilities for NOT NULL:
<synopsis>
-[ CONSTRAINT <replaceable>name</replaceable> ] NOT NULL
+[ CONSTRAINT <replaceable>constraint_name</replaceable> ] NOT NULL
[ {INITIALLY DEFERRED | INITIALLY IMMEDIATE} ]
[ [ NOT ] DEFERRABLE ]
</synopsis>
<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 base table as
+ not necessarily dependent on one particular table as
constraints are, so SQL-92 provides the CREATE ASSERTION statement
as an alternate method for defining a constraint:
</para>
Domain constraint:
<synopsis>
-[ CONSTRAINT <replaceable>name</replaceable> ] CHECK <replaceable>constraint</replaceable>
+[ CONSTRAINT <replaceable>constraint_name</replaceable> ] CHECK <replaceable>constraint</replaceable>
[ {INITIALLY DEFERRED | INITIALLY IMMEDIATE} ]
[ [ NOT ] DEFERRABLE ]
</synopsis>
Table constraint definition:
<synopsis>
-[ CONSTRAINT <replaceable>name</replaceable> ] { PRIMARY KEY ( <replaceable class="parameter">column</replaceable>, ... ) | FOREIGN KEY <replaceable>constraint</replaceable> | UNIQUE <replaceable>constraint</replaceable> | CHECK <replaceable>constraint</replaceable> }
+[ CONSTRAINT <replaceable>constraint_name</replaceable> ] { PRIMARY KEY ( <replaceable class="parameter">column</replaceable>, ... ) | FOREIGN KEY <replaceable>constraint</replaceable> | UNIQUE <replaceable>constraint</replaceable> | CHECK <replaceable>constraint</replaceable> }
[ {INITIALLY DEFERRED | INITIALLY IMMEDIATE} ]
[ [ NOT ] DEFERRABLE ]
</synopsis>
Column constraint definition:
<synopsis>
-[ CONSTRAINT <replaceable>name</replaceable> ] { NOT NULL | PRIMARY KEY | FOREIGN KEY <replaceable>constraint</replaceable> | UNIQUE | CHECK <replaceable>constraint</replaceable> }
+[ CONSTRAINT <replaceable>constraint_name</replaceable> ] { NOT NULL | PRIMARY KEY | FOREIGN KEY <replaceable>constraint</replaceable> | UNIQUE | CHECK <replaceable>constraint</replaceable> }
[ {INITIALLY DEFERRED | INITIALLY IMMEDIATE} ]
[ [ NOT ] DEFERRABLE ]
</synopsis>
<term>INITIALLY IMMEDIATE</term>
<listitem>
<para>
- Check constraint only at the end of the transaction. This
- is the default
+ Check constraint after each statement. This is the default.
</para>
</listitem>
</varlistentry>
<term>INITIALLY DEFERRED</term>
<listitem>
<para>
- Check constraint after each statement.
+ Check constraint only at the end of the transaction.
</para>
</listitem>
</varlistentry>
<para>
table constraint definition:
<synopsis>
-[ CONSTRAINT <replaceable>name</replaceable> ] CHECK ( VALUE <replaceable>condition</replaceable> )
+[ CONSTRAINT <replaceable>constraint_name</replaceable> ] CHECK ( VALUE <replaceable>condition</replaceable> )
[ {INITIALLY DEFERRED | INITIALLY IMMEDIATE} ]
[ [ NOT ] DEFERRABLE ]
</synopsis>
<para>
column constraint definition:
<synopsis>
-[ CONSTRAINT <replaceable>name</replaceable> ] CHECK ( VALUE <replaceable>condition</replaceable> )
+[ CONSTRAINT <replaceable>constraint_name</replaceable> ] CHECK ( VALUE <replaceable>condition</replaceable> )
[ {INITIALLY DEFERRED | INITIALLY IMMEDIATE} ]
[ [ NOT ] DEFERRABLE ]
</synopsis>
<para>
Table Constraint definition:
<synopsis>
-[ CONSTRAINT <replaceable>name</replaceable> ] PRIMARY KEY ( <replaceable>column</replaceable> [, ...] )
+[ CONSTRAINT <replaceable>constraint_name</replaceable> ] PRIMARY KEY ( <replaceable>column</replaceable> [, ... ] )
[ {INITIALLY DEFERRED | INITIALLY IMMEDIATE} ]
[ [ NOT ] DEFERRABLE ]
</synopsis>
<para>
Column Constraint definition:
<synopsis>
-[ CONSTRAINT <replaceable>name</replaceable> ] PRIMARY KEY
+[ CONSTRAINT <replaceable>constraint_name</replaceable> ] PRIMARY KEY
[ {INITIALLY DEFERRED | INITIALLY IMMEDIATE} ]
[ [ NOT ] DEFERRABLE ]
</synopsis>
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