162 lines
4.7 KiB
Plaintext
162 lines
4.7 KiB
Plaintext
<!--
|
|
doc/src/sgml/ref/begin.sgml
|
|
PostgreSQL documentation
|
|
-->
|
|
|
|
<refentry id="sql-begin">
|
|
<indexterm zone="sql-begin">
|
|
<primary>BEGIN</primary>
|
|
</indexterm>
|
|
|
|
<refmeta>
|
|
<refentrytitle>BEGIN</refentrytitle>
|
|
<manvolnum>7</manvolnum>
|
|
<refmiscinfo>SQL - Language Statements</refmiscinfo>
|
|
</refmeta>
|
|
|
|
<refnamediv>
|
|
<refname>BEGIN</refname>
|
|
<refpurpose>start a transaction block</refpurpose>
|
|
</refnamediv>
|
|
|
|
<refsynopsisdiv>
|
|
<synopsis>
|
|
BEGIN [ WORK | TRANSACTION ] [ <replaceable class="parameter">transaction_mode</replaceable> [, ...] ]
|
|
|
|
<phrase>where <replaceable class="parameter">transaction_mode</replaceable> is one of:</phrase>
|
|
|
|
ISOLATION LEVEL { SERIALIZABLE | REPEATABLE READ | READ COMMITTED | READ UNCOMMITTED }
|
|
READ WRITE | READ ONLY
|
|
[ NOT ] DEFERRABLE
|
|
</synopsis>
|
|
</refsynopsisdiv>
|
|
|
|
<refsect1>
|
|
<title>Description</title>
|
|
|
|
<para>
|
|
<command>BEGIN</command> initiates a transaction block, that is,
|
|
all statements after a <command>BEGIN</command> command will be
|
|
executed in a single transaction until an explicit <link
|
|
linkend="sql-commit"><command>COMMIT</command></link> or <link
|
|
linkend="sql-rollback"><command>ROLLBACK</command></link> is given.
|
|
By default (without <command>BEGIN</command>),
|
|
<productname>PostgreSQL</productname> executes
|
|
transactions in <quote>autocommit</quote> mode, that is, each
|
|
statement is executed in its own transaction and a commit is
|
|
implicitly performed at the end of the statement (if execution was
|
|
successful, otherwise a rollback is done).
|
|
</para>
|
|
|
|
<para>
|
|
Statements are executed more quickly in a transaction block, because
|
|
transaction start/commit requires significant CPU and disk
|
|
activity. Execution of multiple statements inside a transaction is
|
|
also useful to ensure consistency when making several related changes:
|
|
other sessions will be unable to see the intermediate states
|
|
wherein not all the related updates have been done.
|
|
</para>
|
|
|
|
<para>
|
|
If the isolation level, read/write mode, or deferrable mode is specified, the new
|
|
transaction has those characteristics, as if
|
|
<link linkend="sql-set-transaction"><command>SET TRANSACTION</command></link>
|
|
was executed.
|
|
</para>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>Parameters</title>
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term><literal>WORK</literal></term>
|
|
<term><literal>TRANSACTION</literal></term>
|
|
<listitem>
|
|
<para>
|
|
Optional key words. They have no effect.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
|
|
<para>
|
|
Refer to <xref linkend="sql-set-transaction"/> for information on the meaning
|
|
of the other parameters to this statement.
|
|
</para>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>Notes</title>
|
|
|
|
<para>
|
|
<link linkend="sql-start-transaction"><command>START TRANSACTION</command></link> has the same functionality
|
|
as <command>BEGIN</command>.
|
|
</para>
|
|
|
|
<para>
|
|
Use <link linkend="sql-commit"><command>COMMIT</command></link> or
|
|
<link linkend="sql-rollback"><command>ROLLBACK</command></link>
|
|
to terminate a transaction block.
|
|
</para>
|
|
|
|
<para>
|
|
Issuing <command>BEGIN</command> when already inside a transaction block will
|
|
provoke a warning message. The state of the transaction is not affected.
|
|
To nest transactions within a transaction block, use savepoints
|
|
(see <xref linkend="sql-savepoint"/>).
|
|
</para>
|
|
|
|
<para>
|
|
For reasons of backwards compatibility, the commas between successive
|
|
<replaceable class="parameter">transaction_modes</replaceable> can be
|
|
omitted.
|
|
</para>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>Examples</title>
|
|
|
|
<para>
|
|
To begin a transaction block:
|
|
|
|
<programlisting>
|
|
BEGIN;
|
|
</programlisting></para>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>Compatibility</title>
|
|
|
|
<para>
|
|
<command>BEGIN</command> is a <productname>PostgreSQL</productname>
|
|
language extension. It is equivalent to the SQL-standard command
|
|
<link linkend="sql-start-transaction"><command>START TRANSACTION</command></link>, whose reference page
|
|
contains additional compatibility information.
|
|
</para>
|
|
|
|
<para>
|
|
The <literal>DEFERRABLE</literal>
|
|
<replaceable class="parameter">transaction_mode</replaceable>
|
|
is a <productname>PostgreSQL</productname> language extension.
|
|
</para>
|
|
|
|
<para>
|
|
Incidentally, the <literal>BEGIN</literal> key word is used for a
|
|
different purpose in embedded SQL. You are advised to be careful
|
|
about the transaction semantics when porting database applications.
|
|
</para>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>See Also</title>
|
|
|
|
<simplelist type="inline">
|
|
<member><xref linkend="sql-commit"/></member>
|
|
<member><xref linkend="sql-rollback"/></member>
|
|
<member><xref linkend="sql-start-transaction"/></member>
|
|
<member><xref linkend="sql-savepoint"/></member>
|
|
</simplelist>
|
|
</refsect1>
|
|
</refentry>
|