sql常用语句

1.EXISTS 运算符

EXISTS 运算符用于判断查询子句是否有记录，如果有一条或多条记录存在返回 True，否则返回 False。

2.Where条件也可以使用 case ..when ..THEN..ELSE..END

   WHERE OrderDate >= CASE ( ISNULL(@OrderDateBegin, '') )  WHEN '' THEN OrderDate ELSE CONVERT(DATETIME, @OrderDateBegin) END   AND OrderDate < ‘2020-10-1‘ END 

3.where条件表达式嵌套子语句

  WHERE (

                  c.departmentid = @departmentid
                  OR c.departmentid IN (
                      SELECT id
                      FROM department(NOLOCK)
                      WHERE tid = @departmentid )

                )  and 1=1

4.存储过程拼接sql，执行sql

DECLARE @SQL varchar(8000) 

SET @SQL = 'Select * from ....'

SET @SQL =  @SQL + '' + ' where 1=1 ' + ' ' ' + @abc + ' ' '

--print(@sql)
EXEC (@SQL)

5. 转换变量日期类型调用日期函数

DATEADD(mm,-1,CONVERT(datetime, @OrderDateBegin))

6. select 字段处可以使用返回一个值的select子语句

SELECT a.UserName,
(select count(1) from ship (NOLOCK) where
CONVERT(varchar(10), Disdate, 20) BETWEEN
CASE(ISNULL(@OrderDateBegin, '')) WHEN '' THEN CONVERT(varchar(10), Disdate, 20) ELSE @OrderDateBegin END ) as Amount, a.Text From ABC a

 7.select 中存在子查询

    SELECT NEWID(), 'H' + CONVERT(VARCHAR(8),r.Date,112) + b.OrderNo

    + '-' + CONVERT(VARCHAR(8),      (   ( SELECT COUNT(1) FROM RepShip WHERE OrderNo= r.OrderNo) + ROW_NUMBER()OVER(PARTITION BY b.OrderNo ORDER BY r.Date  ) )                 )

,....
FROM ship r