常用 SQL 技巧

SQL执行顺序

• 编写顺序

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_params>

• 执行顺序

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_params>

正则表达式使用

正则表达式（Regular Expression）是指一个用来描述或者匹配一系列符合某个句法规则的字符串的单个字符串。

select * from emp where name regexp ‘^T‘;

select * from emp where name regexp ‘2$‘;

select * from emp where name regexp ‘[uvw]‘;

MySQL 常用函数

数字函数

字符串函数

日期函数

聚合函数

MySQL高级【八】常用 SQL 技巧