SQL底层执行原理
#4.1 SELECT 语句的完整结构
/*
#sql92语法：
SELECT ....,....,....(存在聚合函数)
FROM ...,....,....
WHERE 多表的连接条件 AND 不包含聚合函数的过滤条件
GROUP BY ...,....
HAVING 包含聚合函数的过滤条件
ORDER BY ....,...(ASC / DESC )
LIMIT ...,....
#sql99语法：
SELECT ....,....,....(存在聚合函数)
FROM ... (LEFT / RIGHT)JOIN ....ON 多表的连接条件
(LEFT / RIGHT)JOIN ... ON ....
WHERE 不包含聚合函数的过滤条件
GROUP BY ...,....
HAVING 包含聚合函数的过滤条件
ORDER BY ....,...(ASC / DESC )
LIMIT ...,....
*/
#4.2 SQL语句的执行过程：
#FROM ...,...-> ON -> (LEFT/RIGNT JOIN) -> WHERE -> GROUP BY -> HAVING -> SELECT -> DISTINCT ->
# ORDER BY -> LIMIT
标签：...,聚合,函数,....,SQL,原理,SELECT,底层 From： https://www.cnblogs.com/clairedandan/p/18076250