Using Merge with Trigger in SQL Server 2012

Question

I am facing a problem related to merge statement I have merge statement like this

MERGE abc A 
USING xyz B ON A.trans_date = b.trans_date 

WHEN matched AND B.trans_date IS NOT NULL 
   THEN 
       UPDATE 
          SET A.column1 = B.column1, 
              A.column2 = B.column2, 
              A.column3 = B.column3 

WHEN NOT matched BY target AND B.trans_date IS NOT NULL 
   THEN 
      INSERT (column1, column2, column3) 
      VALUES (column1, column2, column3); 

And having a trigger on table ABC like this

ALTER TRIGGER [dbo].[TRG_ABC] 
ON [dbo].[Z_ABC] 
FOR UPDATE 
AS 
    DECLARE @Column4 NUMERIC(9), @Column5 CHAR(1)

    SELECT @Column4 = Column4, @Column5 = Column5 
    FROM inserted 

    UPDATE ABC 
    SET Column5 = CASE 
                     WHEN @Column5 = 'S' 
                        THEN 'Y' 
                        ELSE CASE
                                WHEN @Column5 = 'N' 
                                   THEN 'N' 
                                   ELSE 'U' 
                             END
                  END 
    WHERE Column4 = @Column4

This trigger is not working for updating each row. Is there any wrong with code or any solution for updating each row?

Answer 1

In Sql Server, Trigger will be called at statement level not row level. So the Inserted magic table will have all the updated/inserted records.

Alter the trigger like this

UPDATE a
SET    Column5 = CASE
       WHEN Column5 = 'S' THEN 'Y'
       WHEN Column5 = 'N' THEN 'N'
       ELSE 'U'
       END
FROM   ABC a
INNER JOIN inserted i
ON i.Column4 = a.Column4