sql之查询语句(1)--单表查询

单表查询:

//模糊查询  like+通配符
SELECT * FROM Customer WHERE CustomerName LIKE '张_'
//模糊查询 like+通配符
SELECT * FROM Customer WHERE CustomerName LIKE '张%' ORDER BY CustomerNo DESC
SELECT CustomerName,IdentityNo,Adddress FROM Customer WHERE CustomerNo=4

在查询语句中,使用逻辑和比较运算符:

SELECT CustomerName,IdentityNo,Adddress,Email FROM Customer WHERE CustomerNo=9

--AND 同时满足
SELECT CustomerName,IdentityNo,Adddress,Email FROM Customer WHERE CustomerNo>=1 AND CustomerNo<=5

SELECT CustomerName,IdentityNo,Adddress,Email FROM Customer WHERE CustomerNo BETWEEN 1 AND 5

---CustomerNo=1 OR CustomerNo=5 满足任意一个         

--关键字 IN (集合)
SELECT CustomerName,IdentityNo,Adddress,Email FROM Customer WHERE CustomerNo IN(1,5)

SELECT CustomerName,IdentityNo,Adddress,Email FROM Customer WHERE CustomerNo NOT IN(1,5)

SELECT CustomerName,IdentityNo,Adddress,Email FROM Customer WHERE CustomerNo=1 OR CustomerNo=5

查询指定条数的记录:

SELECT TOP 3 * FROM Customer

IS NULL、IS NOT NULL的使用:

SELECT COUNT(1) AS 'Count' FROM Customer WHERE Email IS NULL

WHERE 子句在前,GROUP BY在后:先对数据进行筛选然后进行分组:

SELECT Adddress,COUNT(1) AS '数量'  FROM Customer WHERE Email IS NOT NULL GROUP BY Adddress 

用Having子句对聚合指定条件:对分组后的数据进行筛选(过滤):

SELECT Adddress,COUNT(1) AS '数量'  FROM Customer WHERE Email IS NOT NULL GROUP BY Adddress
HAVING COUNT(1)>1

ORDER BY子句:

SELECT CustomerName,IdentityNo,Adddress,Email FROM Customer WHERE Email IS NOT NULL  ORDER BY CustomerName DESC

使用DISTINCT关键字排除重复值:根据DISTINCT后面的字段进行去除的:

SELECT DISTINCT Adddress FROM Customer

使用TOP关键字限制返回的行数:

SELECT TOP 4 * FROM Customer --指定返回的数量
SELECT TOP 50 PERCENT * FROM Customer --按比例返回