企劃與您的查詢,因爲它無法評估函數的執行時間的問題。在這種情況下,計劃者獲得該函數的估計執行成本,該成本可以在create function...
或alter function...
中定義。但是,如果您嘗試此查詢:
explain analyse select * from test(10);
您會看到執行時間更爲現實。
比較:
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)
與:
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)
注的最後兩個計劃相似。應該在FROM
子句中調用表函數(在這種情況下返回一組行或表的函數)。在某些情況下,他們可以內聯。
瞭解更多:Inlining of SQL functions。
什麼是較大的查詢?.. –