企划与您的查询,因为它无法评估函数的执行时间的问题。在这种情况下,计划者获得该函数的估计执行成本,该成本可以在create function...
或alter function...
中定义。但是,如果您尝试此查询:
explain analyse select * from test(10);
您会看到执行时间更为现实。
比较:
test=# explain analyse select test(1000);
QUERY PLAN
------------------------------------------------------------------------------------------
Result (cost=0.00..5.25 rows=1000 width=0) (actual time=0.830..1.220 rows=1000 loops=1)
Planning time: 0.038 ms
Execution time: 1.250 ms
(3 rows)
与:
test=# explain analyse select * from test(1000);
QUERY PLAN
----------------------------------------------------------------------------------------------------------------
Limit (cost=0.00..37.42 rows=1000 width=4) (actual time=0.006..0.124 rows=1000 loops=1)
-> Seq Scan on test_table (cost=0.00..2560.28 rows=68428 width=4) (actual time=0.005..0.102 rows=1000 loops=1)
Planning time: 0.130 ms
Execution time: 0.144 ms
(4 rows)
test=# explain analyse select * from test_table limit 1000;
QUERY PLAN
------------------------------------------------------------------------------------------------------------------
Limit (cost=0.00..37.42 rows=1000 width=269) (actual time=0.009..0.118 rows=1000 loops=1)
-> Seq Scan on test_table (cost=0.00..2560.28 rows=68428 width=269) (actual time=0.008..0.097 rows=1000 loops=1)
Planning time: 0.076 ms
Execution time: 0.151 ms
(4 rows)
注的最后两个计划相似。应该在FROM
子句中调用表函数(在这种情况下返回一组行或表的函数)。在某些情况下,他们可以内联。
了解更多:Inlining of SQL functions。
什么是较大的查询?.. –