Trigger in SQL server? - sql-server

Question

I have class table which references student table.
I write a trigger to +1 amount of exellent_eng when insert >=8 score of English subject but it has error:
Msg 4104, Level 16, State 1, Procedure tr_addExellentEnglishStudent, Line 3 [Batch Start Line 1]
The multi-part identifier "x.exellent_Eng" could not be bound.
I'm using SSMS.
CREATE TRIGGER tr_addExellentEnglishStudent ON dbo.dbo_student AFTER INSERT AS
BEGIN
UPDATE dbo.dbo_class
SET x.exellent_Eng += 1
FROM dbo.dbo_class x
JOIN dbo.dbo_student s ON s.class_id = x.class_id
JOIN dbo.dbo_score c ON c.student_id = s.student_id
WHERE (c.subject_id = 1 AND c.score_id >= 8)
END

Answer 1

Few points to correct here:
I don't think you want your trigger on the dbo_student table, because when you first insert a student they won't have any scores. I think you wanted the trigger on adding a new dbo_score record?
As noted in the comments if you alias the table you are updating you should use the notation update <alias> e.g. update x
You don't prefix the column(s) to update with the table name/alias, SQL Server knows which table you are updating.
You probably want to restrict the update to students affected by using the Inserted pseudo-table.
CREATE TRIGGER tr_addExellentEnglishStudent ON dbo.dbo_score
AFTER INSERT AS
BEGIN
UPDATE x SET
exellent_Eng += 1
FROM dbo.dbo_class x
JOIN dbo.dbo_student s ON s.class_id = x.class_id
JOIN dbo.dbo_score c ON c.student_id = s.student_id
WHERE (c.subject_id = 1 AND c.score_id >= 8)
and c.id in (select id from Inserted)
END
Note: this doesn't consider any of the edge cases which might arise e.g. if you update an existing score from 7 to 8 then technically you would want to increase your excellent_Eng result. Similarly if you delete a score or update it from 8 to 7 you would want to decrease it. For these reasons if can be simpler to re-calculate the absolute result rather than making incremental changes.