Question

我有2个这样的表：

Table1:
animal  name  color
cat     bob   red
dog     bill  blue

Table2:  
animal  name
cat     bob
fish    joe

我想查询表1中的所有数据，除非它们具有表2中的唯一标识，因此我会得到蓝色的狗账单，而不是猫，因为它出现在表2中。

我做了：

select t.animal, t.name, t.color
from Table1 as t, Table2 as t2
where NOT(t.animal = t2.animal AND
          t.name = t2.name)
group by t.animal, t.name

有更有效的方法吗？

Answer 1

select t.animal, t.name, t.color
from Table1 as t 
  LEFT JOIN Table2 as t2 ON t.animal = t2.animal and t.name = t2.name
where table2.name is null
group by t.animal, t.name

Answer 2

一个简单的where not exists子句可以解决这个问题：

select t1.animal, t1.name, t1.color
from Table1 t1
where not exists
(
    select 1
    from Table2 t2
    where t2.animal = t1.animal
    and t2.name = t1.name
)

您还可以使用反连接模式：

select t1.animal, t1.name, t1.color
from Table1 t1
left outer join Table2 t2 on t1.animal = t2.animal and t1.name = t2.name
where t2.animal is null

Answer 3

SELECT * FROM table_one t1 
  WHERE t1.animal NOT IN 
                     (SELECT animal FROM table_two)

Mysql：忽略表中的2个不同列

3 个答案: