1
這會給出錯誤:爲什麼工會不能與陳述一起工作?
with a1 as (select 2), a2 as (select 3)
a1 union a2;
-- ERROR: syntax error at or near "a1"
但這不會:
(select 2) union (select 3);
/*
?column?
----------
2
3
(2 rows)
*/
這是怎麼回事?