Decoding COLUMNS_UPDATED Function's results

From MSDN:
"Returns a varbinary bit pattern that indicates the columns in a table or view that were inserted or updated. COLUMNS_UPDATED is used anywhere inside the body of a Transact-SQL INSERT or UPDATE trigger to test whether the trigger should execute certain actions. "

Everything looks easy and cool until you have very wide table and you want to know exactly which column was changed.

COLUMNS_UPDATED() will return strange binary numbers, which represent updated column IDs.

Here I'll present a script for a trigger to get a list of all updated columns:

CREATE TRIGGER <test_trigger> ON <test_Table> AFTER UPDATE AS DECLARE @i SMALLINT = 1; DECLARE @k TINYINT = 1; DECLARE @b TINYINT = 8; DECLARE @m SMALLINT = 1; DECLARE @t TABLE(Column_ID INT) /* Here you capture Binary coded list of changed columns */ DECLARE @Changed_Columns BINARY(128) = COLUMNS_UPDATED(); WHILE @k < 128 BEGIN   WHILE @b > 0   BEGIN     IF CAST(SUBSTRING(@Changed_Columns,@k,1) as SMALLINT) & @m = @m       INSERT INTO @t(Column_ID) VALUES (@i);     SELECT @i += 1, @b -= 1, @m *= 2;   END   SELECT @b = 8, @m = 1, @k += 1; END /* Here you extract list of fields from the schema */ SELECT c.name as Modified_Column FROM sys.triggers as r INNER JOIN sys.columns as c   ON c.object_id = r.parent_id INNER JOIN @t as t ON t.column_id = c.column_id WHERE r.object_id = @@PROCID;

Note: Because SQL Server supports up to 1024 columns in single table my assumption is that output of COLUMNS_UPDATED() can not be larger than 128 bytes.