## Name

SPI_execute — execute a command

## Synopsis

    int SPI_execute(const char * command, bool read_only, int count)

## Description

`SPI_execute` executes the specified SQL command for `count` rows. If `read_only` is `true`, the command must be read-only, and execution overhead is somewhat reduced.

This function may only be called from a connected procedure.

If `count` is zero then the command is executed for all rows that it applies to. If `count` is greater than 0, then the number of rows for which the command will be executed is restricted (much like a `LIMIT` clause). For example,

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

will allow at most 5 rows to be inserted into the table.

You may pass multiple commands in one string, and the commands may be rewritten by rules. `SPI_execute` returns the result for the command executed last. The `count` limit applies to each command separately, but it is not applied to hidden commands generated by rules.

When `read_only` is `false`, `SPI_execute` 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`, 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.

When `read_only` is `true`, `SPI_execute` does not update either the snapshot or the command counter, and it allows only plain `SELECT` 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.

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.

The actual number of rows for which the (last) command was executed is returned in the global variable `SPI_processed` (unless the return value of the function is `SPI_OK_UTILITY`). If the return value of the function is `SPI_OK_SELECT` then you may use the global pointer `SPITupleTable *SPI_tuptable` to access the result rows.

The structure `SPITupleTable` is defined thus:

    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;

`vals` is an array of pointers to rows. (The number of valid entries is given by `SPI_processed`.) `tupdesc` is a row descriptor which you may pass to SPI functions dealing with rows. `tuptabcxt`, `alloced`, and `free` are internal fields not intended for use by SPI callers.

`SPI_finish` frees all `SPITupleTable`s allocated during the current procedure. You can free a particular result table earlier, if you are done with it, by calling `SPI_freetuptable`.

## Arguments

`const char * `command``

  string containing command to execute

`bool `read_only``

  `true` for read-only execution

`int `count``

  maximum number of rows to process or return

## Return Value

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

`SPI_OK_SELECT`

  if a `SELECT` (but not `SELECT INTO`) was executed

`SPI_OK_SELINTO`

  if a `SELECT INTO` was executed

`SPI_OK_DELETE`

  if a `DELETE` was executed

`SPI_OK_INSERT`

  if an `INSERT` was executed

`SPI_OK_UPDATE`

  if an `UPDATE` was executed

`SPI_OK_UTILITY`

  if a utility command (e.g., `CREATE TABLE`) was executed

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

`SPI_ERROR_ARGUMENT`

  if `command` is `NULL` or `count` is less than 0

`SPI_ERROR_COPY`

  if `COPY TO stdout` or `COPY FROM stdin` was attempted

`SPI_ERROR_CURSOR`

  if `DECLARE`, `CLOSE`, or `FETCH` was attempted

`SPI_ERROR_TRANSACTION`

  if `BEGIN`, `COMMIT`, or `ROLLBACK` was attempted

`SPI_ERROR_OPUNKNOWN`

  if the command type is unknown (shouldn't happen)

`SPI_ERROR_UNCONNECTED`

  if called from an unconnected procedure

## Notes

The functions `SPI_execute`, `SPI_exec`, `SPI_execute_plan`, and `SPI_execp` change both `SPI_processed` and `SPI_tuptable` (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 `SPI_execute` or a related function across later calls.