mysql的json查詢：

1、一條普通的SQL

SELECT      <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、Mysql 解析讀取後的SQL

FROM              <left_table>
ON                <join_condition>  <join_type> JOIN  <right_table>
 
 
WHERE              <where_condition>
GROUP BY         <group_by_list>
HAVING           <having_condition>
SELECT DISTINCT  <select_list>
ORDER BY         <order_by_condition>
LIMIT              <limit_number>

mysql解析SQL的時候先從FROM 開始，應為他需要先知道數據來源那些表。

笛卡爾積：A表10條 B表5條 ，笛卡爾積=10*5。

Mysql 學習之 SQL的執行順序