Question

I’ve inherited a legacy database, and many, many fields are no longer being used. I can tell by querying on the last couple of years and seeing which fields are null, to at least get a baseline for where I might look.

Is there an elegant way to figure out which fields in the database are null for all records in a given set?

Answer 1

DECLARE @table NVARCHAR(512);
SET @table = N'dbo.tablename';

DECLARE @sql NVARCHAR(MAX);

SELECT @sql = N'';

SELECT @sql = @sql + QUOTENAME(name) 
     + ' = SUM(CASE WHEN ' + QUOTENAME(name) + ' IS NULL THEN 1 ELSE 0 END),'
  FROM sys.columns
  WHERE object_id = OBJECT_ID(@table)
  AND is_nullable = 1;

SELECT @sql = 'SELECT ' + @sql + ' Total_Count = COUNT(*)
  FROM ' + @table + ';';

EXEC sp_executesql @sql;

Any columns that come out 0 have all nulls (unless the Total_Count column also comes out 0, in which case the table is empty). Note that this query will be pretty expensive on a large table.