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)