SPI_EXECUTE(3)

💖 NAME 💖

SPI_execute — bestie, this is the function that literally just runs a command for you 👑

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✨ SYNOPSIS ✨

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

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🦋 DESCRIPTION 🦋

okay so SPI_execute executes the SQL command you hand it, for count rows. If read_only is true, then the command has to be read-only, and tbh you get a lil discount on execution overhead because of it. slay 💅

This function can only be called from a connected C function. no connection, no party, sorry 🫶

If count is zero, then the command gets executed for all the rows it applies to. If count is greater than zero, then no more than count rows will be retrieved, and execution stops the moment that count is hit — it's giving exactly like adding a LIMIT clause to the query. For example:

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

this one retrieves at most 5 rows from the table. But bestie, listen — that limit only actually does anything when the command returns rows. Like, look:

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

this inserts all the rows from bar, fully ignoring the count parameter 🙈. However, with:

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

at most 5 rows would be inserted, because execution would stop right after the fifth RETURNING result row gets retrieved. the way that works?? iconic.

You can pass multiple commands in one single string — SPI_execute returns the result for the command that got executed last. The count 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. noted 📝

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 doesn't actually change if the current transaction isolation level is SERIALIZABLE or REPEATABLE READ, but in READ COMMITTED mode the snapshot update lets each command 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 updates neither the snapshot nor the command counter, and it only allows plain SELECT commands to appear in the command string. The commands get executed using the snapshot that was previously established for the surrounding query. This execution mode is somewhat faster than the read/write mode, because it eliminates per-command overhead. It also lets genuinely stable functions be built: since successive executions all use the same snapshot, there will be no change in the results. consistency queen 💜

⚠️ 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. don't do it bestie, it's a trap 💀

The actual number of rows for which the (last) command was executed is returned in the global variable SPI_processed. If the return value of the function is SPI_OK_SELECT, SPI_OK_INSERT_RETURNING, SPI_OK_DELETE_RETURNING, SPI_OK_UPDATE_RETURNING, or SPI_OK_MERGE_RETURNING, then you can use the global pointer SPITupleTable *SPI_tuptable to access the result rows. Some utility commands (such as EXPLAIN) also return row sets, and SPI_tuptable will contain the result in these cases too. Some utility commands (COPY, CREATE TABLE AS) don't return a row set, so SPI_tuptable is NULL, but they still return the number of rows processed in SPI_processed. 💅

The structure SPITupleTable is defined thus:

typedef struct SPITupleTable
{
    /* Public members */
    TupleDesc   tupdesc;        /* tuple descriptor */
    HeapTuple  *vals;           /* array of tuples */
    uint64      numvals;        /* number of valid tuples */

    /* Private members, not intended for external callers */
    uint64      alloced;        /* allocated length of vals array */
    MemoryContext tuptabcxt;    /* memory context of result table */
    slist_node  next;           /* link for internal bookkeeping */
    SubTransactionId subid;     /* subxact in which tuptable was created */
} SPITupleTable;

The fields tupdesc, vals, and numvals are the ones SPI callers can actually use; the remaining fields are internal — hands off 🙅‍♀️. vals is an array of pointers to rows. The number of rows is given by numvals (for somewhat historical reasons, this count is also returned in SPI_processed). tupdesc is a row descriptor which you can pass to SPI functions that deal with rows.

SPI_finish frees all SPITupleTables allocated during the current C function. And if you're done with one particular result table earlier than that, you can free it yourself by calling SPI_freetuptable. so thoughtful ✨

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🎀 ARGUMENTS 🎀

• const char * command — the string containing the command to execute 📝
• bool read_only — true for read-only execution 🕊️
• long count — maximum number of rows to return, or 0 for no limit 🔢

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👑 RETURN VALUE 👑

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

• SPI_OK_SELECT — if a SELECT (but not SELECT INTO) was executed ✨
• SPI_OK_SELINTO — if a SELECT INTO was executed ✨
• SPI_OK_INSERT — if an INSERT was executed ✨
• SPI_OK_DELETE — if a DELETE was executed ✨
• SPI_OK_UPDATE — if an UPDATE was executed ✨
• SPI_OK_MERGE — if a MERGE was executed ✨
• SPI_OK_INSERT_RETURNING — if an INSERT RETURNING was executed ✨
• SPI_OK_DELETE_RETURNING — if a DELETE RETURNING was executed ✨
• SPI_OK_UPDATE_RETURNING — if an UPDATE RETURNING was executed ✨
• SPI_OK_MERGE_RETURNING — if a MERGE RETURNING was executed ✨
• SPI_OK_UTILITY — if a utility command (e.g., CREATE TABLE) was executed ✨
• SPI_OK_REWRITTEN — if the command was rewritten into another kind of command (e.g., UPDATE became an INSERT) by a rule ✨

On error, one of the following negative values is returned — yeah, it's giving sad girl hours 😭:

• 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_TRANSACTION — if a transaction manipulation command was attempted (BEGIN, COMMIT, ROLLBACK, SAVEPOINT, PREPARE TRANSACTION, COMMIT PREPARED, ROLLBACK PREPARED, or any variant thereof) 💀
• SPI_ERROR_OPUNKNOWN — if the command type is unknown (shouldn't happen, and that's a direct quote) 💀
• SPI_ERROR_UNCONNECTED — if called from an unconnected C function 💀

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🌈 NOTES 🌈

All SPI query-execution functions set both SPI_processed and SPI_tuptable (just the pointer, not the contents of the structure). So bestie, save these two global variables into local C function variables if you need to access the result table of SPI_execute or another query-execution function across later calls. fr fr, they will get overwritten on you 🫶

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and that's the whole page, no cap — this one came straight out of the PostgreSQL 18.6 documentation, dated 2026. love that for us 💜✨