Question

我有一个可以为空的varchar，即使它是null，我希望我的select返回一个空字符串而不是null。那是

SELECT FIRST, LAST 
FROM CUSTOMER

我想要的是如果FIRST为空，我希望返回为""

Answer 1

您也可以使用

SELECT COALESCE(FIRST, ''), LAST FROM CUSTOMER

这具有更便携的优点（COALESCE是SQL标准的一部分，ISNULL不是）

您还可以使用任意数量的参数，例如

SELECT COALESCE(FIRST, SECOND, THIRD, '')...

COALESCE将使用遇到的第一个非空值

Answer 2

SELECT isnull(FIRST,'') AS FIRST, LAST FROM CUSTOMER

Answer 3

select isNull(First,'') from customer

Answer 4

SELECT COALESCE(FIRST, ''), LAST FROM CUSTOMER

也会起作用

Answer 5

CREATE FUNCTION [dbo].[ParamParserFn]
    (
      @delimString VARCHAR(255) ,
      @delim CHAR(1)
    )
RETURNS @paramtable TABLE
    (
      [Index] INT ,
      [Token] INT
    )
AS 
    BEGIN

        DECLARE @len INT ,
            @index INT ,
            @nextindex INT ,
            @counter INT ,
            @data VARCHAR(50)

        SET @len = DATALENGTH(@delimString)
        SET @index = 0
        SET @nextindex = 0
        SET @counter = 0


        WHILE ( @len + 1 > @index ) 
            BEGIN

                SET @nextindex = CHARINDEX(@delim, @delimString, @index)

                IF ( @nextindex = 0 ) 
                    SET @nextindex = @len + 1



                INSERT  @paramtable
                        SELECT  @counter ,
                                SUBSTRING(@delimString, @index,
                                          @nextindex - @index)


                SELECT  @index = @nextindex + 1 ,
                        @counter = @counter + 1
            END


        RETURN
    END

在SQL Server中，如何选择返回空字符串而不为null时为null

5 个答案: