Question

下面是我的SQL代码：

select count(1) 
from customers 
where id in(
    select custid
    from accounts
    where sid in(72,73,74,75,76,77,78,79)
) 
and id not in(
    select custid 
    from accounts 
    where sid in(80,81)
);

表格已正确编入索引。可以重写此代码以获得更好的性能吗？

Answer 1

您也可以尝试EXISTS：

select count(1) 
from customers c
where exists (
    select 1
    from accounts a
    where sid in(72,73,74,75,76,77,78,79)
    and a.custid = c.custid
) 
and not exists (
    select 1
    from accounts a
    where sid in(80,81)
    and a.custid = c.custid
);

这可能会有帮助，请阅读：Difference between EXISTS and IN in SQL?

Answer 2

加入你的桌子，而不是使用2个subquerys。

SELECT count(1) 
FROM customers c
INNER JOIN accounts a ON c.id = a.sid
WHERE id IN (72, 73, 74, 75, 76, 77, 78, 79)

Answer 3

减号查询可能更有效。像这样：

SELECT count(1) 
FROM 
(
SELECT c.id 
FROM customers c
INNER JOIN accounts a ON c.id = a.sid
WHERE id IN (72, 73, 74, 75, 76, 77, 78, 79)
MINUS
SELECT c.id 
FROM customers c
INNER JOIN accounts a ON c.id = a.sid
WHERE id IN (80,81)
)

为什么SQL＆＃34; NOT IN＆＃34;太慢了？

3 个答案: