Update All Column Values of a table in SQL

You can very easily generate SQL to do the updates, to save you a lot of typing. You can whip up something like this very quickly:

SELECT 'UPDATE [Name] SET ' + COLUMN_NAME + ' = NULL WHERE + ' + COLUMN_NAME + ' = '' ''' FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'Name' AND IS_NULLABLE = 'YES' AND DATA_TYPE IN ('char', 'nchar', 'varchar', 'nvarchar')

Just replace "Name" with the name of your table, and run. Copy the output into a SQL Server Query Manager window, and run it.
The above will update every column of every row in the table to be NULL where the column contains exactly one space.