SQL: ISNULL function with different type of parame

问题:

In SQL Server, ISNULL() function has to same type of parameters.

check_expression

Is the expression to be checked for NULL. check_expression can be of any type.

replacement_value

Is the expression to be returned if check_expression is NULL. replacement_value must have the same type as check_expresssion.

How can I use it with different type of parameter? I want to use with date and string parameter like this ISNULL(A.DATE, '-')

NOTE: Type of A.DATE is datetime.

EDIT-1: My full query which is getting 0 row:

    SELECT A.pkey as KREDİ, A.SUMMARY , D.BayiStatu AS STATU, D.Sorumlu AS SORUMLU, C.BayiSonuc as SONUC, ISNULL( CONVERT(VARCHAR(25), A.CREATED, 112) , '-' ), ISNULL( CONVERT(VARCHAR(25), A.RESOLUTIONDATE, 112) , '-' ), dbo.CUSTVAL(11931, A.ID, 'S') AS BAYİ, ISNULL( CONVERT(VARCHAR(25), dbo.GetLastStatuTime(A.ID), 112) , '-' ) AS SON_STATU_TAR,j2.SUMMARY, ISNULL( CONVERT(VARCHAR(25), j2.CREATED, 112) , '-' ), ISNULL( CONVERT(VARCHAR(25), j2.RESOLUTIONDATE, 112) , '-' ), j3.SUMMARY, ISNULL( CONVERT(VARCHAR(25), j3.CREATED, 112) , '-' ), ISNULL( CONVERT(VARCHAR(25), j3.RESOLUTIONDATE, 112) , '-' )
FROM AspNetServicesDB.dbo.SONUC_MAP C, JİRA.resolution E, jira.issuestatus B, AspNetServicesDB.dbo.STATU_MAP D, Jira.jiraissue A
INNER JOIN Jira.issuelink i
    ON i.SOURCE = A.ID and i.SEQUENCE = 0
INNER JOIN Jira.jiraissue As j2
    ON i.DESTINATION =j2.ID 
LEFT JOIN Jira.issuelink i2 
    ON i2.SOURCE = A.ID  and i2.SEQUENCE = 1
LEFT JOIN Jira.jiraissue As j3 
    ON i2.DESTINATION = j3.ID
WHERE A.issuestatus = B.ID
AND 'BAŞARAN OTOMATİV' = dbo.CUSTVAL(11931, A.ID, 'S')
AND B.pname = D.JiraStatu collate Turkish_CS_AI
AND A.issuetype != 11
AND A.RESOLUTION = E.ID
AND E.pname = C.JiraSonuc collate Turkish_CS_AI

EDIT-2: But this working

select ISNULL( CONVERT(VARCHAR(25), A.RESOLUTIONDATE, 112) , '-' )
FROM Jira.jiraissue A

Could be the reason JOIN ?

回答1:

You can't. The ISNULL function is used by itself as a query result column, or in an expression that eventually is a column in the query result. All fields/rows in a column must have the same data type. So you'll have to choose.

One solution would be to cast the DATE to string, so the result is always a string, but i feel the best solution would be to return NULL for empty dates and let the presentation layer decide whether or not the NULL dates should be shown as - and in what format the non-null dates should be displayed (client locale settings).

With presentation layer, I mean anything that displays or outputs this data, which can be a web page, a CSV exporter, a reporting tool, whatever.

回答2:

Can you simply cast your date as a varchar? Since you're output may not be a valid date anyway, this should work just fine:

ISNULL(CONVERT(varchar(10), A.Date, 101),'-')

回答3:

You need to cast the date to a string if you really want a - instead of null.

declare @T table(adate datetime)
insert into @T values(null)
insert into @T values(getdate())

select isnull(convert(varchar(23), adate, 126), '-')
from @T

回答4:

You can try:

 CASE WHEN A.DATE IS NULL
      THEN '-'
      ELSE CONVERT(VARCHAR(25), A.DATE, 112)
 END

回答5:

I would convert DATE values from [DATE]TIME to VARCHAR using CONVERT/CAST:

SELECT ... ISNULL( CONVERT(VARCHAR(25), A.DATE, 112) , '-' ) AS DATE
FROM ...

Instead of 112 style (yyymmdd) can be used another style: 103 (dd/mm/yyyy), 101 (mm/dd/yyyy) or another style from Date and Time Styles section.