Question

我使用以下查询以逗号分隔来获取列值。

    (SELECT STUFF ((SELECT  ',' + CAST(Proj_ID AS VARCHAR) FROM PROJECT
    left join dbo.PROJ_STA on
    Project.PROJ_STA_ID = Project.PROJ_STA_ID
    WHERE ENTER_DT < DATEADD(Year, -7, GETDATE())  AND PROJ_LFCYC_STA_CD = 'A' AND 
    PROJ_STA.PROJ_STA_DS = 'Cancelled' FOR XML PATH('')), 1, 1, '') 
    AS Enter_Date)

任何人都可以指导我在这里用空字符串替换空值。

更新：

    (SELECT STUFF ((SELECT  ',' + coalesce( CAST(Proj_ID AS VARCHAR), '' ) FROM PROJECT
    left join dbo.PROJ_STA on
    Project.PROJ_STA_ID = Project.PROJ_STA_ID
    WHERE ENTER_DT < DATEADD(Year, -7, GETDATE())  AND PROJ_LFCYC_STA_CD = 'A' AND 
    PROJ_STA.PROJ_STA_DS = 'Cancelled' FOR XML PATH('')), 1, 1, '') 
    AS Enter_Date)

Answer 1

尝试IsNull

select ISNULL(Column,'') as ColumnName

或COALESCE

select COALESCE(NULLIF(ColumnName,''), 'Column')

Answer 2

AdventureWorks数据库中的一个示例

select e.ModifiedDate, ISNULL(p.FirstName,'') as FirstName
from Person.BusinessEntity as e 
    left join Person.Person as p on e.BusinessEntityID = p.BusinessEntityID

通过使用它，如果没有匹配的Person记录，FirstName将显示为空字符串而不是NULL

Answer 3

您可以使用coalesce函数

将空值白化

select coalesce(MyColumn, '')

Coalesce接受任意数量的列或常量，并返回第一个非空的。

您的查询将是：

(SELECT STUFF ((SELECT  ',' + convert(varchar, coalesce( Proj_ID, '' )) FROM PROJECT
left join dbo.PROJ_STA on
Project.PROJ_STA_ID = Project.PROJ_STA_ID
WHERE ENTER_DT < DATEADD(Year, -7, GETDATE())  AND PROJ_LFCYC_STA_CD = 'A' AND 
PROJ_STA.PROJ_STA_DS = 'Cancelled' FOR XML PATH('')), 1, 1, '') 
AS Enter_Date)

如何在SQL中用空字符串替换NULL？

3 个答案: