具有相交和除外的sqlite查询

Question

这是我必须执行的 sqlite 查询，但我想先执行 except 操作，然后执行交集。默认情况下，intersection 的优先级高于 except。有什么办法可以做到这一点吗？

select a, b from table1 intersect select a,b from table2 except  select a, b from table3

我尝试将查询放在方括号中，但它向我抛出错误“[ near “(”:语法错误 ]。

select a, b from table1 intersect (select a,b from table2 except  select a, b from table3)

Answer 1

复合查询不支持括号，但子查询支持:

SELECT a, b FROM table1
INTERSECT
SELECT * FROM (SELECT a, b FROM table2
               EXCEPT
               SELECT a, b FROM table3)

请注意INTERSECT 不的优先级高于EXCEPT，actual rules是:

When three or more simple SELECTs are connected into a compound SELECT, they group from left to right.

因为 INTERSECT 是可交换的，你可以简单地将这个特定的查询写成:

SELECT a, b FROM table2
EXCEPT
SELECT a, b FROM table3
INTERSECT
SELECT a, b FROM table1