Mysql 学习之 SQL的执行顺序
mysql的json查询:
1、一条普通的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 解析读取后的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的时候先从FROM 开始,应为他需要先知道数据来源那些表。
笛卡尔积:A表10条 B表5条 ,笛卡尔积=10*5。
每天用心记录一点点。内容也许不重要,但习惯很重要!