Question

I have a table Students with two fields, StudentName and Grade.
I am trying to write a stored procedure to update the Grade. If the student has an A, I want to change it to B. If they have a B, I want to change it to A. If they have anything else I want to leave it alone. Here is my best attempt

create procedure sp_changegrades
if Grade = 'A' update Students set Grade = 'B'

else if Grade = 'B' update Students set Grade = 'A'

Answer 1

just use CASE

UPDATE Students
SET Grade = 
(
   CASE WHEN Grade = 'A' THEN 'B'
        WHEN Grade = 'B' THEN 'A'
        ELSE Grade     -- "If they have anything else I want to leave it alone."
    END
)

or

UPDATE Students
SET Grade = 
(
   CASE WHEN Grade = 'A' 
        THEN 'B'
        ELSE 'A'
    END
)
WHERE Grade IN ('A','B')