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<refentry id="SQL-ABORT">

SQL92

</title>

<para>

This command is a <productname>Postgres</productname> extension present

This command is a <productname>PostgreSQL</productname> extension present

for historical reasons. <command>ROLLBACK</command> is the <acronym>SQL92</acronym>

equivalent command.

</para>

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Complete list of usable sgml source files in this directory.

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<refentry id="SQL-ALTERGROUP">

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<refentry id="SQL-ALTERTABLE">

<para>

SQL92 specifies some additional capabilities for <command>ALTER TABLE</command>

statement which are not yet directly supported by <productname>Postgres</productname>:

statement which are not yet directly supported by <productname>PostgreSQL</productname>:

<variablelist>

<varlistentry>

<para>

The clauses to rename tables, columns, indexes, and sequences are

<productname>Postgres</productname> extensions from SQL92.

<productname>PostgreSQL</productname> extensions from SQL92.

</para>

</refsect2>

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<refentry id="SQL-ALTERUSER">

</title>

<para>

<command>ALTER USER</command> is used to change the attributes of a user's

<productname>Postgres</productname> account. Attributes not mentioned

<productname>PostgreSQL</productname> account. Attributes not mentioned

in the command retain their previous settings.

</para>

<para>

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<refentry id="SQL-ANALYZE">

</title>

<para>

<command>ANALYZE</command> collects statistics about the contents of

<productname>Postgres</productname> tables, and stores the results in

<productname>PostgreSQL</productname> tables, and stores the results in

the system table <literal>pg_statistic</literal>. Subsequently,

the query planner uses the statistics to help determine the most efficient

execution plans for queries.

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<refentry id="SQL-BEGIN">

</title>

<para>

By default, <productname>Postgres</productname> executes transactions

By default, <productname>PostgreSQL</productname> executes transactions

in <firstterm>unchained mode</firstterm>

(also known as <quote>autocommit</quote> in other database

systems).

<para>

The default transaction isolation level in

<productname>Postgres</productname>

<productname>PostgreSQL</productname>

is READ COMMITTED, where queries inside the transaction see only changes

committed before query execution. So, you have to use

<command>SET TRANSACTION ISOLATION LEVEL SERIALIZABLE</command>

</para>

<para>

If the transaction is committed, <productname>Postgres</productname>

If the transaction is committed, <productname>PostgreSQL</productname>

will ensure either that all updates are done or else that none of

them are done. Transactions have the standard <acronym>ACID</acronym>

(atomic, consistent, isolatable, and durable) property.

<para>

<command>BEGIN</command>

is a <productname>Postgres</productname> language extension.

is a <productname>PostgreSQL</productname> language extension.

There is no explicit <command>BEGIN</command>

command in <acronym>SQL92</acronym>;

transaction initiation is always implicit and it terminates either

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<refentry id="SQL-CLOSE">

Notes

</title>

<para>

<productname>Postgres</productname> does not have

<productname>PostgreSQL</productname> does not have

an explicit <command>OPEN</command> cursor statement;

a cursor is considered open when it is declared.

Use the <command>DECLARE</command> statement to declare a cursor.

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<refentry id="SQL-CLUSTER">

Description

</title>

<para>

<command>CLUSTER</command> instructs <productname>Postgres</productname>

<command>CLUSTER</command> instructs <productname>PostgreSQL</productname>

to cluster the table specified

by <replaceable class="parameter">table</replaceable> approximately

based on the index specified by

on large tables because the rows are fetched from the heap

in index order, and if the heap table is unordered, the

entries are on random pages, so there is one disk page

retrieved for every row moved. <productname>Postgres</productname> has a cache,

retrieved for every row moved. <productname>PostgreSQL</productname> has a cache,

but the majority of a big table will not fit in the cache.

</para>

FROM <replaceable class="parameter">table</replaceable> ORDER BY <replaceable class="parameter">columnlist</replaceable>

</programlisting>

which uses the <productname>Postgres</productname> sorting code in

which uses the <productname>PostgreSQL</productname> sorting code in

the ORDER BY clause to match the index, and which is much faster for

unordered data. You then drop the old table, use

<command>ALTER TABLE...RENAME</command>

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<refentry id="SQL-COMMENT">