mysql 什么时候创建临时表 |mysqlstudy下载

下面列举了几种情况下，MySQL会创建临时表：

• 当执行GROUP BY操作时

SELECT owner, COUNT(*) FROM pet GROUP BY owner;

• 当执行ORDER BY操作时

SELECT name, birth FROM pet ORDER BY birth;

• 当执行UNION操作时

SELECT name FROM pet WHERE species = 'dog'
UNION
SELECT name FROM pet WHERE species = 'cat'

• 当对BLOB或TEXT字段进行排序时

SELECT description FROM products ORDER BY description;

• 当执行多表连接时

SELECT pet.name, owner.name
FROM pet JOIN owner ON pet.owner_id = owner.id

需要注意的是，当查询结束后，MySQL会自动删除临时表。