前言:在使用mysql做count计数多表查询或子查询的时候犯了一个低级的错误:
1248 - Every derived table must have its own alias(每个派生表都必须有自己的别名)
报错sql:
SELECT
count(*)
FROM
(
SELECT
t.id id,
t1.id t1_id,
t2.id t2_id
FROM
t_school t
LEFT JOIN t_teacher t1 ON t.teacherid = t1.id
LEFT JOIN t_user t2 ON t.userid = t2.id
WHERE
1 = 1
)
执行这条语句就会报错:Every derived table must have its own alias。
简单的SQL构成是:select 字段名 from 表名,上面子查询里面查出来的是数据,没有被当成一个表,使用我们只需要在SQL后面加上AS 表名 给他一个表的名字即可
修改过后的SQL:
SELECT
count(*)
FROM
(
SELECT
t.id id,
t1.id t1_id,
t2.id t2_id
FROM
t_school t
LEFT JOIN t_teacher t1 ON t.teacherid = t1.id
LEFT JOIN t_user t2 ON t.userid = t2.id
WHERE
1 = 1
) AS a
加上表名之后即可解决报错了。