where clause: if this value from col x make sure col y is this value
Like this:

select * from myTable 
where colY = 'that' or colX &lt;&gt; 'this'


The standard implementation of any criteria specified as A =&gt; B is as B or not A

Update:

Using this CTE for sample data:

with myTable as (
    select N,colX,colY from ( values
         (1,'this','hey')
        ,(2,'this','that')
        ,(3,'yup', 'yerp')
        ,(4,'yup', 'that')
    ) myTable(N,colX,colY)
)


and this query from above:

select * from myTable 
where colY = 'that' or colX &lt;&gt; 'this'


yields (as required):

N           colX colY
----------- ---- ----
2           this that
3           yup  yerp
4           yup  that

(3 row(s) affected)