具有多个THEN子句的SQL Server CASE语句

Question

I have seen several similar questions but none cover what I need. I need to put another THEN statement after the first one. My column contains int's. When it returns NULL I need it to display a blank space, but when I try the below code, I just get '0'.

CASE 
    WHEN Column1 IS NULL  
    THEN ''
    ELSE Column1
END

If I try to put a sting after THEN then it tells me that it cannot convert it from int. I need to convert it to varchar and then change its output to a blank space afterwards, such as:

eg

CASE 
    WHEN Column1 IS NULL 
    THEN CONVERT(varchar(10), Column1)
    THEN ''
    ELSE Column1
END

Is there a way of doing this?

Thanks Rob

Answer 1

A case expression returns a single value -- with a given type. If you want a string result, then you need to be sure that all paths in the case return strings:

CASE WHEN Column1 IS NULL  
     THEN ''
     ELSE CAST(Column1 AS VARCHAR(255))
END

This is more simply written using COALESCE() :

COALESCE(CAST(Column1 as VARCHAR(255)), '')

You cannot display an integer as a "blank" (other than using a NULL value).