~ubuntu-branches/ubuntu/trusty/postgresql-9.3/trusty-proposed

'\" t

.\"     Title: SPI_execute

.\"    Author: The PostgreSQL Global Development Group

.\" Generator: DocBook XSL Stylesheets v1.78.1 <http://docbook.sf.net/>

.\"      Date: 2016

.\"    Manual: PostgreSQL 9.3.12 Documentation

.\"    Source: PostgreSQL 9.3.12

.\"  Language: English

.\"

.TH "SPI_EXECUTE" "3" "2016" "PostgreSQL 9.3.12" "PostgreSQL 9.3.12 Documentation"

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.SH "NAME"

SPI_execute \- execute a command

.\" SPI_execute

.SH "SYNOPSIS"

.sp

.nf

int SPI_execute(const char * \fIcommand\fR, bool \fIread_only\fR, long \fIcount\fR)

.fi

.SH "DESCRIPTION"

.PP

\fBSPI_execute\fR

executes the specified SQL command for

\fIcount\fR

rows\&. If

\fIread_only\fR

is

true, the command must be read\-only, and execution overhead is somewhat reduced\&.

.PP

This function can only be called from a connected procedure\&.

.PP

If

\fIcount\fR

is zero then the command is executed for all rows that it applies to\&. If

\fIcount\fR

is greater than zero, then no more than

\fIcount\fR

rows will be retrieved; execution stops when the count is reached, much like adding a

LIMIT

clause to the query\&. For example,

.sp

.if n \{\

.RS 4

.\}

.nf

SPI_execute("SELECT * FROM foo", true, 5);

.fi

.if n \{\

.RE

.\}

.sp

will retrieve at most 5 rows from the table\&. Note that such a limit is only effective when the command actually returns rows\&. For example,

.sp

.if n \{\

.RS 4

.\}

.nf

SPI_execute("INSERT INTO foo SELECT * FROM bar", false, 5);

.fi

.if n \{\

.RE

.\}

.sp

inserts all rows from

bar, ignoring the

\fIcount\fR

parameter\&. However, with

.sp

.if n \{\

.RS 4

.\}

.nf

SPI_execute("INSERT INTO foo SELECT * FROM bar RETURNING *", false, 5);

.fi

.if n \{\

.RE

.\}

.sp

at most 5 rows would be inserted, since execution would stop after the fifth

RETURNING

result row is retrieved\&.

.PP

You can pass multiple commands in one string;

\fBSPI_execute\fR

returns the result for the command executed last\&. The

\fIcount\fR

limit applies to each command separately (even though only the last result will actually be returned)\&. The limit is not applied to any hidden commands generated by rules\&.

.PP

When

\fIread_only\fR

is

false,

\fBSPI_execute\fR

increments the command counter and computes a new

snapshot

before executing each command in the string\&. The snapshot does not actually change if the current transaction isolation level is

SERIALIZABLE

or

REPEATABLE READ, but in

READ COMMITTED

mode the snapshot update allows each command to see the results of newly committed transactions from other sessions\&. This is essential for consistent behavior when the commands are modifying the database\&.

.PP

When

\fIread_only\fR

is

true,

\fBSPI_execute\fR

does not update either the snapshot or the command counter, and it allows only plain

\fBSELECT\fR

commands to appear in the command string\&. The commands are executed using the snapshot previously established for the surrounding query\&. This execution mode is somewhat faster than the read/write mode due to eliminating per\-command overhead\&. It also allows genuinely

stable

functions to be built: since successive executions will all use the same snapshot, there will be no change in the results\&.

.PP

It is generally unwise to mix read\-only and read\-write commands within a single function using SPI; that could result in very confusing behavior, since the read\-only queries would not see the results of any database updates done by the read\-write queries\&.

.PP

The actual number of rows for which the (last) command was executed is returned in the global variable

\fISPI_processed\fR\&. If the return value of the function is

SPI_OK_SELECT,

SPI_OK_INSERT_RETURNING,

SPI_OK_DELETE_RETURNING, or

SPI_OK_UPDATE_RETURNING, then you can use the global pointer

SPITupleTable *SPI_tuptable

to access the result rows\&. Some utility commands (such as

\fBEXPLAIN\fR) also return row sets, and

SPI_tuptable

will contain the result in these cases too\&. Some utility commands (\fBCOPY\fR,

\fBCREATE TABLE AS\fR) don\*(Aqt return a row set, so

SPI_tuptable

is NULL, but they still return the number of rows processed in

\fISPI_processed\fR\&.

.PP

The structure

SPITupleTable

is defined thus:

.sp

.if n \{\

.RS 4

.\}

.nf

typedef struct

{

    MemoryContext tuptabcxt;    /* memory context of result table */

    uint32      alloced;        /* number of alloced vals */

    uint32      free;           /* number of free vals */

    TupleDesc   tupdesc;        /* row descriptor */

    HeapTuple  *vals;           /* rows */

} SPITupleTable;

.fi

.if n \{\

.RE

.\}

.sp

vals

is an array of pointers to rows\&. (The number of valid entries is given by

\fISPI_processed\fR\&.)

tupdesc

is a row descriptor which you can pass to SPI functions dealing with rows\&.

tuptabcxt,

alloced, and

free

are internal fields not intended for use by SPI callers\&.

.PP

\fBSPI_finish\fR

frees all

SPITupleTables allocated during the current procedure\&. You can free a particular result table earlier, if you are done with it, by calling

\fBSPI_freetuptable\fR\&.

.SH "ARGUMENTS"

.PP

const char * \fIcommand\fR

.RS 4

string containing command to execute

.RE

.PP

bool \fIread_only\fR

.RS 4

true

for read\-only execution

.RE

.PP

long \fIcount\fR

.RS 4

maximum number of rows to return, or

0

for no limit

.RE

.SH "RETURN VALUE"

.PP

If the execution of the command was successful then one of the following (nonnegative) values will be returned:

.PP

SPI_OK_SELECT

.RS 4

if a

\fBSELECT\fR

(but not

\fBSELECT INTO\fR) was executed

.RE

.PP

SPI_OK_SELINTO

.RS 4

if a

\fBSELECT INTO\fR

was executed

.RE

.PP

SPI_OK_INSERT

.RS 4

if an

\fBINSERT\fR

was executed

.RE

.PP

SPI_OK_DELETE

.RS 4

if a

\fBDELETE\fR

was executed

.RE

.PP

SPI_OK_UPDATE

.RS 4

if an

\fBUPDATE\fR

was executed

.RE

.PP

SPI_OK_INSERT_RETURNING

.RS 4

if an

\fBINSERT RETURNING\fR

was executed

.RE

.PP

SPI_OK_DELETE_RETURNING

.RS 4

if a

\fBDELETE RETURNING\fR

was executed

.RE

.PP

SPI_OK_UPDATE_RETURNING

.RS 4

if an

\fBUPDATE RETURNING\fR

was executed

.RE

.PP

SPI_OK_UTILITY

.RS 4

if a utility command (e\&.g\&.,

\fBCREATE TABLE\fR) was executed

.RE

.PP

SPI_OK_REWRITTEN

.RS 4

if the command was rewritten into another kind of command (e\&.g\&.,

\fBUPDATE\fR

became an

\fBINSERT\fR) by a

rule\&.

.RE

.PP

On error, one of the following negative values is returned:

.PP

SPI_ERROR_ARGUMENT

.RS 4

if

\fIcommand\fR

is

NULL

or

\fIcount\fR

is less than 0

.RE

.PP

SPI_ERROR_COPY

.RS 4

if

\fBCOPY TO stdout\fR

or

\fBCOPY FROM stdin\fR

was attempted

.RE

.PP

SPI_ERROR_TRANSACTION

.RS 4

if a transaction manipulation command was attempted (\fBBEGIN\fR,

\fBCOMMIT\fR,

\fBROLLBACK\fR,

\fBSAVEPOINT\fR,

\fBPREPARE TRANSACTION\fR,

\fBCOMMIT PREPARED\fR,

\fBROLLBACK PREPARED\fR, or any variant thereof)

.RE

.PP

SPI_ERROR_OPUNKNOWN

.RS 4

if the command type is unknown (shouldn\*(Aqt happen)

.RE

.PP

SPI_ERROR_UNCONNECTED

.RS 4

if called from an unconnected procedure

.RE

.SH "NOTES"

.PP

All SPI query\-execution functions set both

\fISPI_processed\fR

and

\fISPI_tuptable\fR

(just the pointer, not the contents of the structure)\&. Save these two global variables into local procedure variables if you need to access the result table of

\fBSPI_execute\fR

or another query\-execution function across later calls\&.