SQL Case WHERE condition, if condition passes check if value is not null-CodePudding

I cannot figure out how to add the last condition. This is part of dynamic code cursor. Cursor consists of a list of table columns. I am comparing values in two tables that are identical in their structure, joining them on PK, and checking one column at a time where the values are not matching. What I need in my last condition is:

if @columnName is 'untCode'
then I want to exclude those rows where TMC.untCode is null
otherwise this condition does not apply

    DECLARE @columnName CHAR(10) = 'untcode';
    
    SELECT MC.@columnName, TMC.@columnName 
    FROM dbo.firstable AS TMC
    INNER JOIN dbo.secondtable AS MC
        ON MC.ID = TMC.ID
        AND MC.Code = TMC.Code        
    WHERE MC.ID = 123
    AND TMC.@columnName<> MC.@columnName
    --How do I add this??
    AND TMC.@columnName CASE 
        WHEN @columnName='untCode' THEN not null 
        ELSE --What???
        END ;

Appreciate the help

CodePudding user response：

As you said it:

    --How do I add this??
    AND NOT (@columnName='untCode' AND TMC.untCode is NULL)

or with a slight change:

    --How do I add this??
    AND (@columnName<>'untCode' OR TMC.untCode is NOT NULL)

But you should correct AND TMC.@columnName<> MC.@columnName as @Larnu said; did you mean AND TMC.columnName=MC.columnName`?