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1ff01b3902
IDs in SGML are case insensitive, and we have accumulated a mix of upper and lower case IDs, including different variants of the same ID. In XML, these will be case sensitive, so we need to fix up those differences. Going to all lower case seems most straightforward, and the current build process already makes all anchors and lower case anyway during the SGML->XML conversion, so this doesn't create any difference in the output right now. A future XML-only build process would, however, maintain any mixed case ID spellings in the output, so that is another reason to clean this up beforehand. Author: Alexander Lakhin <exclusion@gmail.com>
122 lines
4.7 KiB
Plaintext
122 lines
4.7 KiB
Plaintext
<!-- doc/src/sgml/ref/set_constraints.sgml -->
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<refentry id="sql-set-constraints">
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<indexterm zone="sql-set-constraints">
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<primary>SET CONSTRAINTS</primary>
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</indexterm>
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<refmeta>
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<refentrytitle>SET CONSTRAINTS</refentrytitle>
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<manvolnum>7</manvolnum>
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<refmiscinfo>SQL - Language Statements</refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>SET CONSTRAINTS</refname>
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<refpurpose>set constraint check timing for the current transaction</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<synopsis>
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SET CONSTRAINTS { ALL | <replaceable class="parameter">name</replaceable> [, ...] } { DEFERRED | IMMEDIATE }
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</synopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>
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<command>SET CONSTRAINTS</command> sets the behavior of constraint
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checking within the current transaction. <literal>IMMEDIATE</literal>
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constraints are checked at the end of each
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statement. <literal>DEFERRED</literal> constraints are not checked until
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transaction commit. Each constraint has its own
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<literal>IMMEDIATE</literal> or <literal>DEFERRED</literal> mode.
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</para>
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<para>
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Upon creation, a constraint is given one of three
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characteristics: <literal>DEFERRABLE INITIALLY DEFERRED</literal>,
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<literal>DEFERRABLE INITIALLY IMMEDIATE</literal>, or
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<literal>NOT DEFERRABLE</literal>. The third
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class is always <literal>IMMEDIATE</literal> and is not affected by the
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<command>SET CONSTRAINTS</command> command. The first two classes start
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every transaction in the indicated mode, but their behavior can be changed
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within a transaction by <command>SET CONSTRAINTS</command>.
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</para>
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<para>
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<command>SET CONSTRAINTS</command> with a list of constraint names changes
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the mode of just those constraints (which must all be deferrable). Each
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constraint name can be schema-qualified. The
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current schema search path is used to find the first matching name if
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no schema name is specified. <command>SET CONSTRAINTS ALL</command>
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changes the mode of all deferrable constraints.
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</para>
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<para>
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When <command>SET CONSTRAINTS</command> changes the mode of a constraint
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from <literal>DEFERRED</literal>
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to <literal>IMMEDIATE</literal>, the new mode takes effect
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retroactively: any outstanding data modifications that would have
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been checked at the end of the transaction are instead checked during the
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execution of the <command>SET CONSTRAINTS</command> command.
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If any such constraint is violated, the <command>SET CONSTRAINTS</command>
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fails (and does not change the constraint mode). Thus, <command>SET
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CONSTRAINTS</command> can be used to force checking of constraints to
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occur at a specific point in a transaction.
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</para>
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<para>
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Currently, only <literal>UNIQUE</literal>, <literal>PRIMARY KEY</literal>,
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<literal>REFERENCES</literal> (foreign key), and <literal>EXCLUDE</literal>
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constraints are affected by this setting.
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<literal>NOT NULL</literal> and <literal>CHECK</literal> constraints are
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always checked immediately when a row is inserted or modified
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(<emphasis>not</emphasis> at the end of the statement).
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Uniqueness and exclusion constraints that have not been declared
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<literal>DEFERRABLE</literal> are also checked immediately.
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</para>
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<para>
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The firing of triggers that are declared as <quote>constraint triggers</quote>
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is also controlled by this setting — they fire at the same time
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that the associated constraint should be checked.
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</para>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<para>
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Because <productname>PostgreSQL</productname> does not require constraint
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names to be unique within a schema (but only per-table), it is possible
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that there is more than one match for a specified constraint name.
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In this case <command>SET CONSTRAINTS</command> will act on all matches.
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For a non-schema-qualified name, once a match or matches have been found in
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some schema in the search path, schemas appearing later in the path are not
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searched.
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</para>
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<para>
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This command only alters the behavior of constraints within the
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current transaction. Issuing this outside of a transaction block
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emits a warning and otherwise has no effect.
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</para>
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</refsect1>
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<refsect1>
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<title>Compatibility</title>
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<para>
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This command complies with the behavior defined in the SQL
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standard, except for the limitation that, in
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<productname>PostgreSQL</productname>, it does not apply to
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<literal>NOT NULL</literal> and <literal>CHECK</literal> constraints.
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Also, <productname>PostgreSQL</productname> checks non-deferrable
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uniqueness constraints immediately, not at end of statement as the
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standard would suggest.
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</para>
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</refsect1>
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</refentry>
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