如何排除SQL查询结果

Question

我有两个表，每个表都有一列product_id，我想做一个查询，它会排除两个表中找到product_id的产品的结果。

伪示例：

SELECT *
FROM table1
WHERE product_id NOT IN table2

Answer 1

如果两个表中的product_ids都不存在于另一个表中，则必须进行联合，因为mysql不支持完全外连接：

select t1.product_id, 't1' as table_name
from table1 t1 left join table2 t2
on t1.product_id = t2.product_id where t2.product_id is null 
union
select t2.product_id, 't2' as table_name
from table1 t1 right join table2 t2
on t1.product_id = t2.product_id where t1.product_id is null     

Answer 2

试试这个：

select * from table1 
where product_id not in (select product_id from table2) as p;