SQL 书写顺序与执行顺序

① SQL语句书写顺序：

SELECT DISTINCT
　　<select_list>
FROM 
　　<left_table> <join_type>
JOIN  <right_table>  ON  <join_condition>
WHERE 
　　<where_condition>
GROUP BY 
      <group_by_list>
HAVING
　　<having_condition>
ORDER BY
　　<order_by_condition>
LIMIT <limit_number>
 
② SQL执行顺序：

1.FROM  <left_table>

2.ON  <join_condition>

3.<join_type> JOIN  <right_table>
 
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>