SQL基础系列(2)-内置函数--转载w3school

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1.    日期函数

Mssql：

SELECT GETDATE()

返回当前日期和时间

SELECT DATEPART(yyyy,OrderDate) AS OrderYear,

DATEPART(mm,OrderDate) AS OrderMonth,

DATEPART(dd,OrderDate) AS OrderDay

FROM Orders1

WHERE OrderId=1

返回日期/时间的单独部分

SELECT OrderId,OrderDate,DATEADD(day,2,OrderDate) AS OrderPayDate

FROM Orders1

在日期中添加或减去指定的时间间隔

SELECT DATEDIFF(day,‘2016-06-08‘,‘2016-06-08‘) AS DiffDate

返回两个日期之间的时间

CONVERT() 函数是把日期转换为新数据类型的通用函数。

CONVERT() 函数可以用不同的格式显示日期/时间数据。

SELECT CONVERT(VARCHAR(19),GETDATE())

SELECT CONVERT(VARCHAR(10),GETDATE(),110)

SELECT CONVERT(VARCHAR(11),GETDATE(),106)

SELECT CONVERT(VARCHAR(24),GETDATE(),113)

Mysql

2.    ISNULL IFNULL

Mssql

SELECT ProductName,UnitPrice*(UnitsInStock+ISNULL(UnitsOnOrder,0))

FROM Products

Mysql

SELECT ProductName,UnitPrice*(UnitsInStock+IFNULL(UnitsOnOrder,0))

FROM Products

SELECT ProductName,UnitPrice*(UnitsInStock+COALESCE(UnitsOnOrder,0))

FROM Products

3.    函数

AVG 函数返回数值列的平均值。NULL 值不包括在计算中。

SELECT AVG(OrderPrice) AS OrderAverage FROM Orders

用在where后

SELECT Customer FROM Orders

WHERE OrderPrice>(SELECT AVG(OrderPrice) FROM Orders)

Count

SELECT COUNT(column_name) FROM table_name

COUNT(column_name) 函数返回指定列的值的数目（NULL 不计入）

SELECT COUNT(*) FROM table_name

COUNT(*) 函数返回表中的记录数

SELECT FIRST(column_name) FROM table_name

SELECT LAST(column_name) FROM table_name

MAX 函数返回一列中的最大值。NULL 值不包括在计算中。

SELECT MAX(column_name) FROM table_name

MIN 函数返回一列中的最小值。NULL 值不包括在计算中

SELECT MIN(column_name) FROM table_name

求和

SELECT SUM(column_name) FROM table_name

分组

SELECT column_name, aggregate_function(column_name)

FROM table_name

WHERE column_name operator value

GROUP BY column_name

Having

SELECT column_name, aggregate_function(column_name)

FROM table_name

WHERE column_name operator value

GROUP BY column_name

HAVING aggregate_function(column_name) operator value

Where后不能直接接聚合函数，加having即可

SELECT Customer,SUM(OrderPrice) FROM Orders

WHERE Customer=‘Bush‘ OR Customer=‘Adams‘

GROUP BY Customer

HAVING SUM(OrderPrice)>1500

UCASE 函数把字段的值转换为大写

SELECT UCASE(column_name) FROM table_name

LCASE 函数把字段的值转换为小写

SELECT LCASE(column_name) FROM table_name

MID 函数用于从文本字段中提取字符

SELECT MID(column_name,start[,length]) FROM table_name

LEN 函数返回文本字段中值的长度

SELECT LEN(City) as LengthOfCity FROM Persons

ROUND 函数用于把数值字段舍入为指定的小数位数

SELECT ROUND(column_name,decimals) FROM table_name

NOW 函数返回当前的日期和时间

SELECT ProductName, UnitPrice, Now() as PerDate FROM Products

FORMAT 函数用于对字段的显示进行格式化

SELECT FORMAT(column_name,format) FROM table_name

SQL基础系列(2)-内置函数--转载w3school

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原文地址：http://www.cnblogs.com/zijiyanxi/p/5572025.html