Mysql错误信息汇总

目录：

1. Every derived table must have its own alias

内容：

1. Every derived table must have its own alias

SELECT app, s, 
(
    SELECT COUNT(1) FROM sessions AS b WHERE s >= starttime AND s < endtime
) AS COUNT
FROM (
    SELECT DISTINCT app, starttime AS s FROM sessions
) AS b

注意红色加粗代码“AS b”，每个派生出来的表都必须有一个自己的别名，加个别名就可以了。

2. You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near

报这个错因为创建存储过程的时候少了红框的内容：

3.  No database selected

错误代码： 1046
No database selected

此错原因是没有选择数据库

4. Not unique table/alias: 'dept_manager'

# 错误SQL
SELECT * FROM dept_manager, dept_manager;
# 正确SQL
SELECT * FROM dept_manager AS a, dept_manager AS b;

表dept_manager与自己级联时，要指定别名，不然会报此错误。