mysql函数 引发子查询的三种情况 1.由比较运算符 2.由IN 或 NOT IN 3.由EXISTS 或 NOT EXISTS
多表更新
UPDATE table_name INNER JOIN table_name ON condition SET
多表连接
SELECT column_name1,column_name2,... FROM table_name1 [AS alias] [INNER JOIN || LEFT JOIN || RIGHT JOIN] table_name2 [AS alias] ON condition [INNER JOIN || LEFT JOIN || RIGHT JOIN] table_name3 [AS alias] ON condition ...
对多表连接的结果排序(EVERY DERIVE SHOULD HAVE ITS OWN ALIAS)
SELECT * FROM (SELECT column_name1,column_name2,... FROM table_name1 [AS alias] [INNER JOIN || LEFT JOIN || RIGHT JOIN] table_name2 [AS alias] ON condition [INNER JOIN || LEFT JOIN || RIGHT JOIN] table_name3 [AS alias] ON condition ...) AS alias ORDER BY alias.column_name [ASC || DESC];
外连接
当尝试查找column_name IS NULL 但数据表设为NOT NULL 查找到符合条件的记录后即停止查找
无限级分类表设计：在同一张表中查询父类与子类，自连接和起别名查询名字重复的记录，删除id较大的重复记录，按序显示记录
