dblink_get_result
dblink_get_result — gets an async query result
Synopsis
dblink_get_result(text connname [, bool fail_on_error]) returns setof record
Description
dblink_get_result collects the results of an asynchronous query previously sent withdblink_send_query. If the query is not already completed,dblink_get_result will wait until it is.
Arguments
connnameName of the connection to use.
fail_on_errorIf true (the default when omitted) then an error thrown on the remote side of the connection causes an error to also be thrown locally. If false, the remote error is locally reported as a NOTICE, and the function returns no rows.
Return Value
For an async query (that is, an SQL statement returning rows), the function returns the row(s) produced by the query. To use this function, you will need to specify the expected set of columns, as previously discussed fordblink.
For an async command (that is, an SQL statement not returning rows), the function returns a single row with a single text column containing the command's status string. It is still necessary to specify that the result will have a single text column in the callingFROM clause.
Notes
This functionmust be called ifdblink_send_query returned 1. It must be called once for each query sent, and one additional time to obtain an empty set result, before the connection can be used again.
When usingdblink_send_query anddblink_get_result,dblink fetches the entire remote query result before returning any of it to the local query processor. If the query returns a large number of rows, this can result in transient memory bloat in the local session. It may be better to open such a query as a cursor withdblink_open and then fetch a manageable number of rows at a time. Alternatively, use plaindblink(), which avoids memory bloat by spooling large result sets to disk.
Examples
contrib_regression=# SELECT dblink_connect('dtest1', 'dbname=contrib_regression'); dblink_connect---------------- OK(1 row)contrib_regression=# SELECT * FROMcontrib_regression-# dblink_send_query('dtest1', 'select * from foo where f1 < 3') AS t1; t1---- 1(1 row)contrib_regression=# SELECT * FROM dblink_get_result('dtest1') AS t1(f1 int, f2 text, f3 text[]); f1 | f2 | f3----+----+------------ 0 | a | {a0,b0,c0} 1 | b | {a1,b1,c1} 2 | c | {a2,b2,c2}(3 rows)contrib_regression=# SELECT * FROM dblink_get_result('dtest1') AS t1(f1 int, f2 text, f3 text[]); f1 | f2 | f3----+----+----(0 rows)contrib_regression=# SELECT * FROMcontrib_regression-# dblink_send_query('dtest1', 'select * from foo where f1 < 3; select * from foo where f1 > 6') AS t1; t1---- 1(1 row)contrib_regression=# SELECT * FROM dblink_get_result('dtest1') AS t1(f1 int, f2 text, f3 text[]); f1 | f2 | f3----+----+------------ 0 | a | {a0,b0,c0} 1 | b | {a1,b1,c1} 2 | c | {a2,b2,c2}(3 rows)contrib_regression=# SELECT * FROM dblink_get_result('dtest1') AS t1(f1 int, f2 text, f3 text[]); f1 | f2 | f3----+----+--------------- 7 | h | {a7,b7,c7} 8 | i | {a8,b8,c8} 9 | j | {a9,b9,c9} 10 | k | {a10,b10,c10}(4 rows)contrib_regression=# SELECT * FROM dblink_get_result('dtest1') AS t1(f1 int, f2 text, f3 text[]); f1 | f2 | f3----+----+----(0 rows)