mysql 左连接 left join 查询结果比原条件数据量少

原sql

-- 结果为 200
SELECT COUNT(id) FROM a WHERE order_flow = 1 AND order_status = 1 AND deleted = 0

-- 结果为 180
SELECT COUNT(id) FROM b WHERE state = 0 AND deleted =0

左连接查询结果为0，需求为找到这相差的20条数据

写法1

-- 结果为0条
SELECT o.* from 
 a o
left join
 b c
 on o.enterprise_id=c.id
where o.order_status=1 and o.deleted=0 and c.deleted=0 and c.state = 0
and c.id is null;

写法2（结果正确）

-- 结果有20条

SELECT o.* from a o
left join (SELECT id FROM b WHERE state = 0 AND deleted =0) c on o.enterprise_id=c.id
where o.order_flow=1 and o.order_status=1 and o.deleted=0 
and c.id is null;

原因为写法1中 c.deleted=0 and c.state = 0 对连接数据结果造成了影响

所以应该首先把连接的表做出来后在连接