Sql语句执行顺序
7) SELECT
8) DISTINCT <select_list>
1) FROM <left_table>
3) <join_type> JOIN <right_table>
2) ON <join_condition>
4) WHERE <where_condition>
5) GROUP BY <group_by_list>
6) HAVING <having_condition>
9) ORDER BY <order_by_condition>
10) LIMIT <limit_number>
