SQL Server Merge Upsert仅执行更新而不进行插入

Question

I want to record student movement when they swipe their cards on the door. Every time a card id and name is presented, I want to check if its a new combination which is not already in the students table. If not present then insert a new record with FirstEntry and LastEntry being the same date and cardid and name being the one that is sent in to the respective parameters. If combination already present then only update the [LastEntry] field. At the moment my query is only updating existing records, which means only the [LastEntry] field gets updated. For update this is normal. However, it doesn't insert a new record for a new entry. CardID and Name are the composite primary keys here on the table.

• I don't want to use the IF Exists(Select...) method for acheiving this.
• I want to use MERGE only.
• This action is to be done on the same table without using any temp tables
• After performing the action I want to see the affected records in either the update or insert scenarios. Only the following fields to be shown [cardid, name, FirstEntry, LastEntry] and not the other fields in the table.
• The table has other columns which I don't want to show or return.

Here is my statement which only does updates

            MERGE INTO
            Students AS T
        USING 
            (SELECT cardid,  name, FirstEntry, LastEntry from Students where cardid = @id and name = @name) AS S
        ON
            (S.cardid = T.cardid
            AND
            S.name = T.name)
        WHEN MATCHED THEN
            UPDATE SET LastEntry =  @DT
        WHEN NOT MATCHED THEN
            INSERT (cardid,  name, FirstEntry, LastEntry) VALUES(@id, @name, @DT, @DT )
        OUTPUT $action, S.cardid,  S.name, S.FirstEntry, S.LastEntry;

Along with updates I want it to effect inserts as well for new records

Answer 1

Your using clause shouldn't be querying the Students table. That's where you put the new values you want to insert or update. It should look like this:

MERGE INTO
   Students AS T
USING 
   (SELECT @id as cardid, @name as name, @DT as FirstEntry, @DT as LastEntry) AS S
ON
   (S.cardid = T.cardid
   AND
   S.name = T.name)
WHEN MATCHED THEN
   UPDATE SET LastEntry =  s.LastEntry
WHEN NOT MATCHED THEN
   INSERT (cardid,  name, FirstEntry, LastEntry) VALUES(s.cardid, s.name, s.FirstEntry, s.LastEntry )
OUTPUT $action, inserted.cardid,  inserted.name, inserted.FirstEntry, inserted.LastEntry;

EDIT

Your output clause should probably be using inserted.<col_name> instead of S.<col_name> for the returned column names to see the new inserted or updated values. You can also use deleted.<col_name> if you want to see the value before it got updated (will be null for inserts).