postgresql/doc/src/sgml/ref/begin.sgml

<REFENTRY ID="SQL-BEGINWORK">
 <REFMETA>
  <REFENTRYTITLE>
   BEGIN WORK
  </REFENTRYTITLE>
  <REFMISCINFO>SQL - Language Statements</REFMISCINFO>
 </REFMETA>
 <REFNAMEDIV>
  <REFNAME>
   BEGIN WORK
  </REFNAME>
  <REFPURPOSE>
   Begins a transaction
  </REFPURPOSE>
  
  
 <REFSYNOPSISDIV>
  <REFSYNOPSISDIVINFO>
   <DATE>1998-09-08</DATE>
  </REFSYNOPSISDIVINFO>
  <SYNOPSIS>  
BEGIN [ WORK | TRANSACTION ]
  </SYNOPSIS>
  
  <REFSECT2 ID="R2-SQL-BEGINWORK-1">
   <REFSECT2INFO>
    <DATE>1998-09-08</DATE>
   </REFSECT2INFO>
   <TITLE>
    Inputs
   </TITLE>
   <PARA>
       None
  </REFSECT2>
  
  <REFSECT2 ID="R2-SQL-BEGINWORK-2">
   <REFSECT2INFO>
    <DATE>1998-09-08</DATE>
   </REFSECT2INFO>
   <TITLE>
    Outputs
   </TITLE>
   <PARA>
   </PARA>
   <VARIABLELIST>
    <VARLISTENTRY>
     <TERM>
      <replaceable>status</replaceable>
     </TERM>
     <LISTITEM>
      <PARA>
       <VARIABLELIST>
	<VARLISTENTRY>
	 <TERM>
	  <returnvalue>BEGIN</returnvalue>
	 </TERM>
	 <LISTITEM>
	  <PARA>
	   This signifies that a new transaction has been started.
	  </PARA>
	 </LISTITEM>
	</VARLISTENTRY>
	<VARLISTENTRY>
	 <TERM>
	   <returnvalue>NOTICE:  BeginTransactionBlock and not in default state</returnvalue>
	 </TERM>
	 <LISTITEM>
	  <PARA>
	   This indicates that a transaction was already in progress.
The current transaction is not affected.
	  </PARA>
	 </LISTITEM>
	</VARLISTENTRY>
       </variablelist>
      </para>
     </LISTITEM>
    </VARLISTENTRY>
   </VARIABLELIST>
  </REFSECT2>
 </REFSYNOPSISDIV>
 
 <REFSECT1 ID="R1-SQL-BEGINWORK-1">
  <REFSECT1INFO>
   <DATE>1998-09-08</DATE>
  </REFSECT1INFO>
  <TITLE>
   Description
  </TITLE>
  <para>
   <command>BEGIN</command> initiates a user transaction
 which <productname>Postgres</productname> will
   guarantee is serializable with respect to all concurrently
   executing transactions. <productname>Postgres</productname> uses two-phase
 locking
   to perform this task. If the transaction is committed,
   <productname>Postgres</productname> will ensure either that all updates are
 done or else
   that none of
   them are done. Transactions have the standard ACID
   (atomic, consistent, isolatable, and durable) property.
  </para>
  
  <REFSECT2 ID="R2-SQL-BEGINWORK-3">
   <REFSECT2INFO>
    <DATE>1998-09-08</DATE>
   </REFSECT2INFO>
   <TITLE>
    Notes
   </TITLE>
   <PARA>
    The keyword TRANSACTION is just a cosmetic alternative to WORK.
    Neither keyword need be specified.
   </PARA>

   <PARA>
    Refer to the <command>LOCK</command> statement for further information
 about locking tables inside a transaction.
   </PARA>
   
   <PARA>
    Use <command>COMMIT</command> or <command>ROLLBACK</command>
 to terminate a transaction.
   </PARA>
  </REFSECT2>
  
 <REFSECT1 ID="R1-SQL-BEGINWORK-2">
  <TITLE>
   Usage
  </TITLE>
  <PARA>To begin a user transaction:

  <ProgramListing>
BEGIN WORK;
  </ProgramListing>
 </REFSECT1>
 
 <REFSECT1 ID="R1-SQL-BEGINWORK-3">
  <TITLE>
   Compatibility
  </TITLE>
  <PARA>
    <command>BEGIN</command>
 is a <productname>Postgres</productname> language extension.
  
  <REFSECT2 ID="R2-SQL-BEGINWORK-4">
     <REFSECT2INFO>
    <DATE>1998-09-08</DATE>
   </REFSECT2INFO>
   <TITLE>
    SQL92
   </TITLE>
   <PARA> 
    There is no explicit BEGIN WORK command in <acronym>SQL92</acronym>;
 transaction initiation
    is always implicit and it terminates either with a COMMIT or with
    a ROLLBACK statement.
   </PARA>
  </refsect2>
 </refsect1>
</REFENTRY>
 
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