一、SQL语句执行顺序
(1) FROM <left table>
(2) ON <join_condition>
(3) <join_type> JOIN <right_talbe>
(4) WHERE <where_condition>
(5) GROUP BY <group_by_list>
(6) HAVING <having_condition>
(7) SELECT
(8) DISTINCT <select_list>
(9) ORDER BY <order_by_condition>
(10) LIMIT <limit_number>
1、from 对查询指定的表计算笛卡尔积
2、on 按照 join_condition 过滤数据
3、join 添加关联外部表数据
4、where 按照where_condition过滤数据
5、group by 进行分组操作
6、having 按照having_condition过滤数据
7、select 选择指定的列
8、distinct 指定列去重
9、order by 按照order_by_condition排序
10、limit 取出指定记录量
