mysql

cross join ：笛卡尔交集。

Inner join ：内连接。

left join ：只要满足左边表的需求就可以了,右表有无都可以。

right join ：只要满足右表的需求就可以了,左表有无都可以。

UNION

SQL Statement 1

UNION

SQL Statement 2

注意：查看一样的字段,union 是将两个结果集并在一起,筛选出重复的数据, union all 只是简单的将两个结果结果合并,但是union all 比union 快。

CREATE UNIQUE INDEX 索引名称

ON 表名称 (列名称)

CREATE INDEX 索引名称

ON 表名称 (列名称)

CREATE INDEX PersonIndex

ON Person (LastName)

CREATE INDEX PersonIndex

ON Person (LastName DESC)

CREATE INDEX PersonIndex

ON Person (LastName, FirstName)

SELECT column,SUM(column) FROM table

GROUP BY column

HAVING SUM(column) condition value

SELECT Company,SUM(Amount) FROM Sales

GROUP BY Company

HAVING SUM(Amount)>10000

SELECT * FROM Persons WHERE FirstName LIKE '___h' (下划线表示三个字符，表示匹配前面有三个字符最后面是h)

SELECT * FROM Persons WHERE FirstName LIKE [houhuiyang]; (匹配[]里面的所有字符)

SELECT * FROM Persons WHERE FirstName LIKE [a-zA-Z]; (匹配[]里面小写a到z大写的A-Z)

SELECT * FROM Persons WHERE FirstName REGEXP ‘^[houhuiyang]’;(匹配正则表达式的内容)