Find fields that aren't used (have all nulls)

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

Answer 1

This gives you the count of all records with NULL fields which you can compare to the count of all the records

SELECT COUNT(*)
FROM Table1
WHERE COALESCE (Field1, Field2, etc) IS NULL

Answer 2

Is this what you need?

  SELECT count(*)
  FROM table
  WHERE field IS NULL

or of course

 SELECT SUM(CASE WHEN field IS NULL THEN 1 ELSE 0 END) AS [field is null count]
        COUNT(*) as [total count]
 FROM table

also works and you can do it for a bunch of fields at once.

---

Stealing Aaron Bertrand's template:

DECLARE @tableName NVARCHAR(512)

SET @tableName = N'dbo.tablename';

DECLARE @sql NVARCHAR(MAX);

SELECT @sql = N'';

SELECT @sql = @sql + N' SUM(CASE WHEN ' + QUOTENAME(name) + ' IS NULL THEN 1 ELSE 0 END) AS ['+name+' null count], '
FROM sys.columns
WHERE object_id = OBJECT_ID(@tableName) AND is_nullable = 1;

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

EXEC sp_executesql @sql;

Answer 3

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.