1 SUM
SUM是一个求和函数,返回指定列值的总和。SUM 只能用于数字列。 其中忽略 Null 值。
语法
SUM ( [ ALL | DISTINCT ] expression ) OVER ( [ partition_by_clause ] order_by_clause )
示例
SELECT SUM([UnitsInStock]) FROM [dbo].[Product]
SELECT SUM(DISTINCT([UnitsInStock])) FROM [dbo].[Product]
SUM可以与GROUP BY一起使用,计算每个分组的总和。
SELECT [CategoryID],SUM([UnitsInStock]) FROM [dbo].[Product] GROUP BY [CategoryID]
2 AVG
返回组中各值的平均值。 其中忽略 Null 值。
语法
AVG ( [ ALL | DISTINCT ] expression ) OVER ( [ partition_by_clause ] order_by_clause )
示例
SELECT AVG([UnitsInStock]) FROM [dbo].[Product]
SELECT [CategoryID],AVG([UnitsInStock]) FROM [dbo].[Product] GROUP BY [CategoryID]
3 MAX
返回表达式中的最大值。
语法
MAX ( [ ALL | DISTINCT ] expression ) OVER ( [ partition_by_clause ] order_by_clause )
示例
SELECT MAX([UnitsInStock]) FROM [dbo].[Product]
SELECT [CategoryID],MAX([UnitsInStock]) FROM [dbo].[Product] GROUP BY [CategoryID]
4 MIN
返回表达式中的最小值。
语法
MIN ( [ ALL | DISTINCT ] expression )
OVER ( [ partition_by_clause ] order_by_clause )
示例
SELECT MIN([UnitsInStock]) FROM [dbo].[Product]
SELECT [CategoryID],MIN([UnitsInStock])
FROM [dbo].[Product]
GROUP BY [CategoryID]
在查询语句中同时使用MIN、MAX函数
SELECT [CategoryID],MIN([UnitsInStock]), MAX([UnitsInStock]) FROM [dbo].[Product] GROUP BY [CategoryID]
where条件过滤
SELECT [CategoryID],MIN([UnitsInStock]), MAX([UnitsInStock]) FROM [dbo].[Product] WHERE [CategoryID] IN (1, 2, 3) GROUP BY [CategoryID]
5 COUNT
返回组中的项数。 COUNT 与 COUNT_BIG 函数类似。 两个函数唯一的差别是它们的返回值。 COUNT 始终返回 int 数据类型值。 COUNT_BIG 始终返回 bigint 数据类型值。
语法
COUNT ( { [ [ ALL | DISTINCT ] expression ] | * } ) OVER ( [ partition_by_clause ] order_by_clause )
示例
SELECT COUNT([UnitsInStock]) FROM [dbo].[Product]
SELECT [CategoryID],COUNT([UnitsInStock]) FROM [dbo].[Product] GROUP BY [CategoryID]
COUNT(*)函数用于计算查询中返回的行数。
SELECT COUNT(*) FROM [dbo].[Product]
COUNT函数的其他计算形式,如COUNT(1)、COUNT([PrimaryKey])、COUNT([ColumnName]),COUNT()函数会忽略NULL的记录,在使用COUNT([ColumnName])计算行数时,字段ColumnName值为NULL的记录不会计算。
SELECT COUNT([ProductName]) FROM [dbo].[Product]
等价于:
SELECT COUNT([ProductName]) FROM [dbo].[Product] WHERE [ProductName] IS NOT NULL
在COUNT()方法中使用DISTINCT
SELECT COUNT(DISTINCT [CategoryID]) FROM [dbo].[Product]
6 HAVING
HAVING子句仅用于带有GROUP BY子句的查询语句中,WHERE子句用于每一行(在变成一个组的某一部分之前),而HAVING子句用于分组的聚合值。
SELECT [CategoryID], COUNT(*) AS Products FROM [dbo].[Product] GROUP BY [CategoryID]
SELECT [CategoryID], COUNT(*) AS Products FROM [dbo].[Product] WHERE [Quantity] >= 10 GROUP BY [CategoryID]
SELECT [CategoryID], COUNT(*) AS Products FROM [dbo].[Product] WHERE [Quantity] >= 10 GROUP BY [CategoryID] HAVING COUNT(*) > 1