Update "NULL" string to Actual NULL value

Question

I have a table that contains NULL values but the problem is that some of the values are actually string "NULL" and not actual NULLS so when you trying something like

where date is null

it will not return the fields that have the "NULL" string.

What I am needing to do is run an update of the whole table that will convert all string "NULLS" to the actual NULL value. The "NULL" strings happen throughout all columns of the table so it is not just 1 column that needs to be updated. I am not sure how to approach this scenario. I'm thinking I might need to use a loop since i have many columns but then again there might be a simple solution without having to use a loop. What would be the best way to resolve this issue?

• ypercubeᵀᴹ: Are we talking about 4-5 columns? Or about 100 columns?
• Juan Velez: more like 30 to 40 columns

Answer 1

DECLARE @sql NVARCHAR(MAX);
SET @sql = N'';
SELECT @sql = @sql + '
 ' + QUOTENAME(name) + ' = CASE
 WHEN ' + QUOTENAME(name) + ' = ''NULL'' THEN NULL ELSE '
 + QUOTENAME(name) + ' END,'
FROM sys.columns
WHERE [object_id] = OBJECT_ID('dbo.YourTableName')
AND system_type_id IN (35,99,167,175,231,239);
SELECT @sql = N'UPDATE dbo.YourTableName SET ' + LEFT(@sql, LEN(@sql)-1) + ';';
PRINT @sql;
--EXEC sp_executesql @sql;

• Travis: @Aaron, where could we find the lookup table for the system_type_id? Thanks in advance.
• Aaron Bertrand: They're in sys.types
• Travis: @Aaron, maybe I am not in the right page. This is the MSDN page (msdn.microsoft.com/en-us/library/ms188021.aspx) I was looking at, but it doesn't have the list of system_type_id and its corresponding data type.
• Aaron Bertrand: @Travis the documentation does not list all of the values, it just describes the view itself. If you want to see the values, just run a select: SELECT * FROM sys.types;
• Travis: @Aaron. Never mind. It is in the sys.types table..