sql语句

select(查询一个关键字或多个关键字)

from（查询某个表）

order by（排序）

asc（在order by后面加asc变成升序）

desc（在order by后面加desc变成倒排序）

len()（进行一个字符串的长短排序）

distinct（去重复）

union（有一个去重复的效果）

union all(不去重复效果)

inner join （内连接）

left join（左连接）

right join （右连接）

insert into （向表中插入数据）

max（取最大值）

min（最小值）

or (或)

and（与）

set IDENTITY_INSERT sales.promotions ON;（想指定promotion_id 数，就要进行上面语句进行打开）

set IDENTITY_INSERT sales.promotions OFF;（成功插入Id数之后，要进行一个关闭操作）

delete from sales.visits;（删除表里面的数据）

truncate table sales.visits;（完全删除数据，连ID也删除）

select @@IDENTITY (要紧跟着错误的语言查询)

sql语句

–查询表的数据
SELECT * FROM dbo.teacher

–右连接
SELECT * FROM dbo.course AS r1
right join dbo.sc AS k1 ON r1.cno=k1.cno

–左连接
SELECT * FROM dbo.course AS u1
left join dbo.sc AS y1 ON u1.cno=y1.cno

–内连接
SELECT * FROM dbo.course AS u1
inner join dbo.sc AS g1 ON u1.cno=g1.cno

–内连接，进行一个平均数
SELECT o1.cno,AVG(o2.score) FROM dbo.course AS o1
inner join dbo.sc AS o2 ON o1.cno=o2.cno
GROUP BY o1.cno

–右连接，GROUP BY b1.cno 分组操作，COUNT 进行相同行数的统计，SUM计算总数
SELECT b1.cno, COUNT(c1.score),SUM(c1.score) FROM dbo.course AS b1
right join dbo.sc AS c1 ON b1.cno=c1.cno
GROUP BY b1.cno

–内连接，分组，计算总数
SELECT d1.cname,SUM(p1.score) FROM dbo.course d1
inner join dbo.sc AS p1 ON d1.cno =p1.cno
GROUP BY d1.cname

–分组，获取最大值
SELECT o.sno,MAX(o.score) FROM dbo.sc AS o
GROUP BY o.sno

–分组，获取最小值
SELECT cno,MIN(score) FROM dbo.sc
GROUP BY cno

–插入数据
INSERT INTO dbo.sc(sno,cno,score)
VALUES(‘c008’,‘c008’,23.80);

–修改数据
UPDATE dbo.sc
set sno=‘s008’
WHERE sno=‘c008’

–删除数据
DELETE dbo.sc
WHERE sno=‘s008’

–小到大排序
SELECT * from dbo.sc
ORDER BY score desc

–大到小排序
SELECT * from dbo.course
ORDER BY tno asc,cno desc

–字符长度
SELECT cno,len(cname)长度,tno FROM dbo.course

–分组
SELECT *FROM dbo.sc
ORDER BY score desc
OFFSET(2-1)*3 ROWS
FETCH NEXT 3 ROWS ONLY

–去重复
SELECT distinct sno FROM dbo.sc

–不等于空
SELECT * FROM dbo.sc
right join dbo.course ON dbo.sc.cno=dbo.course.cno
WHERE dbo.sc.sno is not null

–and（与）
SELECT * FROM dbo.sc
right join dbo.course ON dbo.sc.cno=dbo.course.cno
WHERE dbo.sc.sno is null and dbo.sc.cno is null and dbo.sc.score is null

–or (或)
SELECT * FROM dbo.sc
right join dbo.course ON dbo.sc.cno=dbo.course.cno
WHERE dbo.sc.sno is null or dbo.course.cno is null