1SPI_EXECUTE(3)           PostgreSQL 12.2 Documentation          SPI_EXECUTE(3)
2
3
4

NAME

6       SPI_execute - execute a command
7

SYNOPSIS

9       int SPI_execute(const char * command, bool read_only, long count)
10

DESCRIPTION

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
16       This function can only be called from a connected C function.
17
18       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
23           SPI_execute("SELECT * FROM foo", true, 5);
24
25       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
28           SPI_execute("INSERT INTO foo SELECT * FROM bar", false, 5);
29
30       inserts all rows from bar, ignoring the count parameter. However, with
31
32           SPI_execute("INSERT INTO foo SELECT * FROM bar RETURNING *", false, 5);
33
34       at most 5 rows would be inserted, since execution would stop after the
35       fifth RETURNING result row is retrieved.
36
37       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
43       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
52       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
61       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
66       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
77       The structure SPITupleTable is defined thus:
78
79           typedef struct
80           {
81               MemoryContext tuptabcxt;    /* memory context of result table */
82               uint64      alloced;        /* number of alloced vals */
83               uint64      free;           /* number of free vals */
84               TupleDesc   tupdesc;        /* row descriptor */
85               HeapTuple  *vals;           /* rows */
86           } SPITupleTable;
87
88
89       vals is an array of pointers to rows. (The number of valid entries is
90       given by SPI_processed.)  tupdesc is a row descriptor which you can
91       pass to SPI functions dealing with rows.  tuptabcxt, alloced, and free
92       are internal fields not intended for use by SPI callers.
93
94       SPI_finish frees all SPITupleTables allocated during the current C
95       function. You can free a particular result table earlier, if you are
96       done with it, by calling SPI_freetuptable.
97

ARGUMENTS

99       const char * command
100           string containing command to execute
101
102       bool read_only
103           true for read-only execution
104
105       long count
106           maximum number of rows to return, or 0 for no limit
107

RETURN VALUE

109       If the execution of the command was successful then one of the
110       following (nonnegative) values will be returned:
111
112       SPI_OK_SELECT
113           if a SELECT (but not SELECT INTO) was executed
114
115       SPI_OK_SELINTO
116           if a SELECT INTO was executed
117
118       SPI_OK_INSERT
119           if an INSERT was executed
120
121       SPI_OK_DELETE
122           if a DELETE was executed
123
124       SPI_OK_UPDATE
125           if an UPDATE was executed
126
127       SPI_OK_INSERT_RETURNING
128           if an INSERT RETURNING was executed
129
130       SPI_OK_DELETE_RETURNING
131           if a DELETE RETURNING was executed
132
133       SPI_OK_UPDATE_RETURNING
134           if an UPDATE RETURNING was executed
135
136       SPI_OK_UTILITY
137           if a utility command (e.g., CREATE TABLE) was executed
138
139       SPI_OK_REWRITTEN
140           if the command was rewritten into another kind of command (e.g.,
141           UPDATE became an INSERT) by a rule.
142
143       On error, one of the following negative values is returned:
144
145       SPI_ERROR_ARGUMENT
146           if command is NULL or count is less than 0
147
148       SPI_ERROR_COPY
149           if COPY TO stdout or COPY FROM stdin was attempted
150
151       SPI_ERROR_TRANSACTION
152           if a transaction manipulation command was attempted (BEGIN, COMMIT,
153           ROLLBACK, SAVEPOINT, PREPARE TRANSACTION, COMMIT PREPARED, ROLLBACK
154           PREPARED, or any variant thereof)
155
156       SPI_ERROR_OPUNKNOWN
157           if the command type is unknown (shouldn't happen)
158
159       SPI_ERROR_UNCONNECTED
160           if called from an unconnected C function
161

NOTES

163       All SPI query-execution functions set both SPI_processed and
164       SPI_tuptable (just the pointer, not the contents of the structure).
165       Save these two global variables into local C function variables if you
166       need to access the result table of SPI_execute or another
167       query-execution function across later calls.
168
169
170
171PostgreSQL 12.2                      2020                       SPI_EXECUTE(3)
Impressum