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PQspecPrepare(3) libpqtypes Manual PQspecPrepare(3)
PQspecPrepare - Prepares a libpqtypes specifier format string.
int PQspecPrepare(PGconn *conn, const char *name,
const char *format, int is_stmt);
void PQclearSpecs(PGconn *conn);
PQspecPrepare allows an application to prepare specifier format strings
that will be used frequently. By preparing a specifier format string,
one avoids the parsing and type handler lookup costs. This becomes a
significant win when managing large result sets or arrays, where the
specifier format, like "%int4 %text %bytea", must be prepared for each
As with PQregisterXXX, only specifier format strings prepared prior to
the creation of a PGresult or PGparam, will be available for use. This
is because the prepared type spec is cached within a PGconn object and
copied to all subsequent PGparam and PGresult objects.
Every prepared type spec is given a name, which is used as its unique
identifier. To use a prepared type spec, the name is provided where
ever a regular specifier format string is allowed, like PQputf or
PQgetf. The name must be proceeded by a '@' AT sign. For more
information about the syntax, see the pqt-specs(3) man page.
The format argument is the specifier format string being prepared.
When this is NULL, the name prepared type spec is removed from the
PGconn's internal array.
The is_stmt argument indicates if a parementerized statement version of
format should be cached along with the prepared type spec. This means
all type specifiers in format, like "%int4", will be converted to "$1"
syntax. When is_stmt is non-zero, a statement will created and cached.
For more information on specifer format string to paremterized
statements, see the PQputf(3) man page. NOTE: to use a prepared type
spec with execution functions like PQexecf, is_stmt must be set to non-
PQclearSpecs removes all prepared specifiers from the given PGconn, as
opposed to removing them one by one by setting PQspecPrepare's format
argument to NULL. A good use for this is after a PQresetXXX call when
it might be desired to re-prepare all type specifiers.
Functions that support the use of a prepared type spec are: PQputf,
PQputvf, PQgetf, PQgetvf, PQexecf, PQexecvf, PQsendf, PQsendvf,
HINT: A good rule of thumb for using prepared type specs, is when there
are a large number of PQputf/PQgetf calls per statement execution.
This commonly occurs when dealing with large result sets and arrays.
PQspecPrepare and PQclearSpecs return a nonzero value on success and
zero if it fails. Use PQgeterror() to get an error message.
This example prepares a type spec and issues some PQputf calls.
if(!PQspecPrepare(conn, "prepared_spec", "%int4 %text", 0))
fprintf(stderr, "PQspecPrepare: %s0, PQgeterror());
/* create after preparing spec */
param = PQparamCreate(conn);
for(i=0; i < 100000; i++)
/* NOTE: nothing else can be in format string */
PQputf(param, "@prepared_spec", 4, "text");
/* This elects to prepare a statement as well. After this returns,
* "SELECT myfunc($1, $2)" will be cached along with the prepared spec.
PQspecPrepare(conn, "myfunc", "SELECT myfunc(%int4, %text)", 1);
/* "myfunc" tells execf to execute "SELECT myfunc($1, $2)". If is_stmt
* was set to zero during the PQspecPrepare, the below would be invalid
* because execf doesn't know what to execute.
PQexecf(conn, "@myfunc", 123, "text");
/* clear'm all */
A contribution of eSilo, LLC. for the PostgreSQL Database Management
System. Written by Andrew Chernow.
Report bugs to <firstname.lastname@example.org>.
Copyright (c) 2011 eSilo, LLC. All rights reserved.
This is free software; see the source for copying conditions. There is
NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
pqt-specs(3), PQgetf(3), PQputf(3).
libpqtypes 2011 PQspecPrepare(3)