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><H1
><A
NAME="SPI-SPI-PREPARE"
></A
>SPI_prepare</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN64766"
></A
><H2
>Name</H2
>SPI_prepare&nbsp;--&nbsp;prepare a statement, without executing it yet</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN64769"
></A
><H2
>Synopsis</H2
><PRE
CLASS="SYNOPSIS"
>SPIPlanPtr SPI_prepare(const char * <TT
CLASS="PARAMETER"
>command</TT
>, int <TT
CLASS="PARAMETER"
>nargs</TT
>, Oid * <TT
CLASS="PARAMETER"
>argtypes</TT
>)</PRE
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN64774"
></A
><H2
>Description</H2
><P
>   <CODE
CLASS="FUNCTION"
>SPI_prepare</CODE
> creates and returns a prepared
   statement for the specified command, but doesn't execute the command.
   The prepared statement can later be executed repeatedly using
   <CODE
CLASS="FUNCTION"
>SPI_execute_plan</CODE
>.
  </P
><P
>   When the same or a similar command is to be executed repeatedly, it
   is generally advantageous to perform parse analysis only once, and
   might furthermore be advantageous to re-use an execution plan for the
   command.
   <CODE
CLASS="FUNCTION"
>SPI_prepare</CODE
> converts a command string into a
   prepared statement that encapsulates the results of parse analysis.
   The prepared statement also provides a place for caching an execution plan
   if it is found that generating a custom plan for each execution is not
   helpful.
  </P
><P
>   A prepared command can be generalized by writing parameters
   (<TT
CLASS="LITERAL"
>$1</TT
>, <TT
CLASS="LITERAL"
>$2</TT
>, etc.) in place of what would be
   constants in a normal command.  The actual values of the parameters
   are then specified when <CODE
CLASS="FUNCTION"
>SPI_execute_plan</CODE
> is called.
   This allows the prepared command to be used over a wider range of
   situations than would be possible without parameters.
  </P
><P
>   The statement returned by <CODE
CLASS="FUNCTION"
>SPI_prepare</CODE
> can be used
   only in the current invocation of the procedure, since
   <CODE
CLASS="FUNCTION"
>SPI_finish</CODE
> frees memory allocated for such a
   statement.  But the statement can be saved for longer using the functions
   <CODE
CLASS="FUNCTION"
>SPI_keepplan</CODE
> or <CODE
CLASS="FUNCTION"
>SPI_saveplan</CODE
>.
  </P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN64790"
></A
><H2
>Arguments</H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>const char * <TT
CLASS="PARAMETER"
>command</TT
></TT
></DT
><DD
><P
>      command string
     </P
></DD
><DT
><TT
CLASS="LITERAL"
>int <TT
CLASS="PARAMETER"
>nargs</TT
></TT
></DT
><DD
><P
>      number of input parameters (<TT
CLASS="LITERAL"
>$1</TT
>, <TT
CLASS="LITERAL"
>$2</TT
>, etc.)
     </P
></DD
><DT
><TT
CLASS="LITERAL"
>Oid * <TT
CLASS="PARAMETER"
>argtypes</TT
></TT
></DT
><DD
><P
>      pointer to an array containing the <ACRONYM
CLASS="ACRONYM"
>OID</ACRONYM
>s of
      the data types of the parameters
     </P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN64814"
></A
><H2
>Return Value</H2
><P
>   <CODE
CLASS="FUNCTION"
>SPI_prepare</CODE
> returns a non-null pointer to an
   <TT
CLASS="TYPE"
>SPIPlan</TT
>, which is an opaque struct representing a prepared
   statement.  On error, <TT
CLASS="SYMBOL"
>NULL</TT
> will be returned,
   and <TT
CLASS="VARNAME"
>SPI_result</TT
> will be set to one of the same
   error codes used by <CODE
CLASS="FUNCTION"
>SPI_execute</CODE
>, except that
   it is set to <TT
CLASS="SYMBOL"
>SPI_ERROR_ARGUMENT</TT
> if
   <TT
CLASS="PARAMETER"
>command</TT
> is <TT
CLASS="SYMBOL"
>NULL</TT
>, or if
   <TT
CLASS="PARAMETER"
>nargs</TT
> is less than 0, or if <TT
CLASS="PARAMETER"
>nargs</TT
> is
   greater than 0 and <TT
CLASS="PARAMETER"
>argtypes</TT
> is <TT
CLASS="SYMBOL"
>NULL</TT
>.
  </P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN64829"
></A
><H2
>Notes</H2
><P
>   If no parameters are defined, a generic plan will be created at the
   first use of <CODE
CLASS="FUNCTION"
>SPI_execute_plan</CODE
>, and used for all
   subsequent executions as well.  If there are parameters, the first few uses
   of <CODE
CLASS="FUNCTION"
>SPI_execute_plan</CODE
> will generate custom plans
   that are specific to the supplied parameter values.  After enough uses
   of the same prepared statement, <CODE
CLASS="FUNCTION"
>SPI_execute_plan</CODE
> will
   build a generic plan, and if that is not too much more expensive than the
   custom plans, it will start using the generic plan instead of re-planning
   each time.  If this default behavior is unsuitable, you can alter it by
   passing the <TT
CLASS="LITERAL"
>CURSOR_OPT_GENERIC_PLAN</TT
> or
   <TT
CLASS="LITERAL"
>CURSOR_OPT_CUSTOM_PLAN</TT
> flag to
   <CODE
CLASS="FUNCTION"
>SPI_prepare_cursor</CODE
>, to force use of generic or custom
   plans respectively.
  </P
><P
>   Although the main point of a prepared statement is to avoid repeated parse
   analysis and planning of the statement, <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> will
   force re-analysis and re-planning of the statement before using it
   whenever database objects used in the statement have undergone
   definitional (DDL) changes since the previous use of the prepared
   statement.  Also, if the value of <A
HREF="runtime-config-client.html#GUC-SEARCH-PATH"
>search_path</A
> changes
   from one use to the next, the statement will be re-parsed using the new
   <TT
CLASS="VARNAME"
>search_path</TT
>.  (This latter behavior is new as of
   <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> 9.3.)  See <A
HREF="sql-prepare.html"
>PREPARE</A
> for more information about the behavior of prepared
   statements.
  </P
><P
>   This function should only be called from a connected procedure.
  </P
><P
>   <TT
CLASS="TYPE"
>SPIPlanPtr</TT
> is declared as a pointer to an opaque struct type in
   <TT
CLASS="FILENAME"
>spi.h</TT
>.  It is unwise to try to access its contents
   directly, as that makes your code much more likely to break in
   future revisions of <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>.
  </P
><P
>   The name <TT
CLASS="TYPE"
>SPIPlanPtr</TT
> is somewhat historical, since the data
   structure no longer necessarily contains an execution plan.
  </P
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