1SPI_EXECUTE(3) PostgreSQL 13.4 Documentation SPI_EXECUTE(3)
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6 SPI_execute - execute a command
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9 int SPI_execute(const char * command, bool read_only, long count)
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12 SPI_execute executes the specified SQL command for count rows. If
13 read_only is true, the command must be read-only, and execution
14 overhead is somewhat reduced.
15 This function can only be called from a connected C function.
17 If count is zero then the command is executed for all rows that it
19 applies to. If count is greater than zero, then no more than count rows
20 will be retrieved; execution stops when the count is reached, much like
21 adding a LIMIT clause to the query. For example,
22 SPI_execute("SELECT * FROM foo", true, 5);
24 will retrieve at most 5 rows from the table. Note that such a limit is
26 only effective when the command actually returns rows. For example,
27 SPI_execute("INSERT INTO foo SELECT * FROM bar", false, 5);
29 inserts all rows from bar, ignoring the count parameter. However, with
31 SPI_execute("INSERT INTO foo SELECT * FROM bar RETURNING *", false, 5);
33 at most 5 rows would be inserted, since execution would stop after the
35 fifth RETURNING result row is retrieved.
36 You can pass multiple commands in one string; SPI_execute returns the
38 result for the command executed last. The count limit applies to each
39 command separately (even though only the last result will actually be
40 returned). The limit is not applied to any hidden commands generated by
41 rules.
42 When read_only is false, SPI_execute increments the command counter and
44 computes a new snapshot before executing each command in the string.
45 The snapshot does not actually change if the current transaction
46 isolation level is SERIALIZABLE or REPEATABLE READ, but in READ
47 COMMITTED mode the snapshot update allows each command to see the
48 results of newly committed transactions from other sessions. This is
49 essential for consistent behavior when the commands are modifying the
50 database.
51 When read_only is true, SPI_execute does not update either the snapshot
53 or the command counter, and it allows only plain SELECT commands to
54 appear in the command string. The commands are executed using the
55 snapshot previously established for the surrounding query. This
56 execution mode is somewhat faster than the read/write mode due to
57 eliminating per-command overhead. It also allows genuinely stable
58 functions to be built: since successive executions will all use the
59 same snapshot, there will be no change in the results.
60 It is generally unwise to mix read-only and read-write commands within
62 a single function using SPI; that could result in very confusing
63 behavior, since the read-only queries would not see the results of any
64 database updates done by the read-write queries.
65 The actual number of rows for which the (last) command was executed is
67 returned in the global variable SPI_processed. If the return value of
68 the function is SPI_OK_SELECT, SPI_OK_INSERT_RETURNING,
69 SPI_OK_DELETE_RETURNING, or SPI_OK_UPDATE_RETURNING, then you can use
70 the global pointer SPITupleTable *SPI_tuptable to access the result
71 rows. Some utility commands (such as EXPLAIN) also return row sets, and
72 SPI_tuptable will contain the result in these cases too. Some utility
73 commands (COPY, CREATE TABLE AS) don't return a row set, so
74 SPI_tuptable is NULL, but they still return the number of rows
75 processed in SPI_processed.
76 The structure SPITupleTable is defined thus:
78 typedef struct SPITupleTable
80 {
81 /* Public members */
82 TupleDesc tupdesc; /* tuple descriptor */
83 HeapTuple *vals; /* array of tuples */
84 uint64 numvals; /* number of valid tuples */
85 /* Private members, not intended for external callers */
87 uint64 alloced; /* allocated length of vals array */
88 MemoryContext tuptabcxt; /* memory context of result table */
89 slist_node next; /* link for internal bookkeeping */
90 SubTransactionId subid; /* subxact in which tuptable was created */
91 } SPITupleTable;
92 The fields tupdesc, vals, and numvals can be used by SPI callers; the
94 remaining fields are internal. vals is an array of pointers to rows.
95 The number of rows is given by numvals (for somewhat historical
96 reasons, this count is also returned in SPI_processed). tupdesc is a
97 row descriptor which you can pass to SPI functions dealing with rows.
98 SPI_finish frees all SPITupleTables allocated during the current C
100 function. You can free a particular result table earlier, if you are
101 done with it, by calling SPI_freetuptable.
102
104 const char * command
105 string containing command to execute
106 bool read_only
108 true for read-only execution
109 long count
111 maximum number of rows to return, or 0 for no limit
112
114 If the execution of the command was successful then one of the
115 following (nonnegative) values will be returned:
116 SPI_OK_SELECT
118 if a SELECT (but not SELECT INTO) was executed
119 SPI_OK_SELINTO
121 if a SELECT INTO was executed
122 SPI_OK_INSERT
124 if an INSERT was executed
125 SPI_OK_DELETE
127 if a DELETE was executed
128 SPI_OK_UPDATE
130 if an UPDATE was executed
131 SPI_OK_INSERT_RETURNING
133 if an INSERT RETURNING was executed
134 SPI_OK_DELETE_RETURNING
136 if a DELETE RETURNING was executed
137 SPI_OK_UPDATE_RETURNING
139 if an UPDATE RETURNING was executed
140 SPI_OK_UTILITY
142 if a utility command (e.g., CREATE TABLE) was executed
143 SPI_OK_REWRITTEN
145 if the command was rewritten into another kind of command (e.g.,
146 UPDATE became an INSERT) by a rule.
147 On error, one of the following negative values is returned:
149 SPI_ERROR_ARGUMENT
151 if command is NULL or count is less than 0
152 SPI_ERROR_COPY
154 if COPY TO stdout or COPY FROM stdin was attempted
155 SPI_ERROR_TRANSACTION
157 if a transaction manipulation command was attempted (BEGIN, COMMIT,
158 ROLLBACK, SAVEPOINT, PREPARE TRANSACTION, COMMIT PREPARED, ROLLBACK
159 PREPARED, or any variant thereof)
160 SPI_ERROR_OPUNKNOWN
162 if the command type is unknown (shouldn't happen)
163 SPI_ERROR_UNCONNECTED
165 if called from an unconnected C function
166
168 All SPI query-execution functions set both SPI_processed and
169 SPI_tuptable (just the pointer, not the contents of the structure).
170 Save these two global variables into local C function variables if you
171 need to access the result table of SPI_execute or another
172 query-execution function across later calls.
173PostgreSQL 13.4 2021 SPI_EXECUTE(3)