Replace null string with null value

Question

I have a table that has a string value of 'null' that I wish to replace with an actual NULL value.

However if I try to do the following in my select

Select Replace(Mark,'null',NULL) from tblname

It replaces all rows and not just the rows with the string. If I change it to

Select Replace(Mark,'null',0) from tblname

It does what I would expect and only change the ones with string 'null'

Answer 1

You can use NULLIF:

SELECT NULLIF(Mark,'null') 
FROM tblname;