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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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>EXPLAIN</TITLE
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>PostgreSQL User's Guide</TH
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><H1
>EXPLAIN</H1
><DIV
CLASS="REFNAMEDIV"
><H2
>Name</H2
>EXPLAIN &#8212; Shows statement execution details</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><PRE
CLASS="SYNOPSIS"
>EXPLAIN [ VERBOSE ] <TT
CLASS="REPLACEABLE"
><I
>query</I
></TT
>        </PRE
><DIV
CLASS="REFSECT2"
><H3
>Inputs</H3
><P
>&#13;<P
></P
></P><DL
><DT
>VERBOSE</DT
><DD
><P
>Flag to show detailed query plan.&#13;</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>query</I
></TT
></DT
><DD
><P
>Any <TT
CLASS="REPLACEABLE"
><I
>query</I
></TT
>.&#13;</P
></DD
></DL
><P>&#13;</P
></DIV
><DIV
CLASS="REFSECT2"
><H3
>Outputs</H3
><P
>&#13;<P
></P
></P><DL
><DT
>NOTICE:  QUERY PLAN:
<TT
CLASS="REPLACEABLE"
><I
>plan</I
></TT
></DT
><DD
><P
>Explicit query plan from the <SPAN
CLASS="PRODUCTNAME"
>Postgres</SPAN
> backend.&#13;</P
></DD
><DT
>EXPLAIN</DT
><DD
><P
>Flag sent after query plan is shown.&#13;</P
></DD
></DL
><P>&#13;</P
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><H2
>Description</H2
><P
>   This command outputs details about the supplied query.
   The default output is the computed query cost. 
   VERBOSE displays the full query plan and cost to your screen,
   and pretty-prints the plan to the postmaster log file.   &#13;</P
><DIV
CLASS="REFSECT2"
><H3
>Notes</H3
><P
>There is only sparse documentation on the optimizer's use of cost
information in <SPAN
CLASS="PRODUCTNAME"
>Postgres</SPAN
>.
General information on cost estimation for query optimization
can be found in database textbooks.
Refer to the <I
CLASS="CITETITLE"
>Programmer's Guide</I
>
in the chapters on indexes and the genetic query optimizer for
more information.&#13;</P
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><H2
>Usage</H2
><P
>To show a query plan for a simple query:

<PRE
CLASS="PROGRAMLISTING"
>postgres=&#62; explain select * from foo;
NOTICE:  QUERY PLAN:

Seq Scan on foo  (cost=0.00 size=0 width=4)

EXPLAIN</PRE
>&#13;</P
></DIV
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><H2
>Compatibility</H2
><P
></P
><DIV
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><H3
>SQL92</H3
><P
>   There is no EXPLAIN statement defined in SQL92.</P
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