Question

update: This is more of a maintenance issue than the normal case.

I have the following table:

CourseId   StudentId
---------------------
1          1
1          2
2          1

CourseId and StudentId are composite primary key.

Let’s say I wanted to update where courseid=1 to courseid=2 for some reason. This will cause a primary key constraint issue.

What are some different ways you could solved this?

Answer 1

1. Disable/Drop the primary key constraint

2. Run the UPDATE statement:

   UPDATE YOUR_TABLE
      SET courseid = 2
    WHERE courseid = 1
   

3. Remove duplicates – this solution assumes SQL Server 2005+:

   WITH duplicates AS (
       SELECT t.courseid,
              t.studentid,
              ROW_NUMBER() OVER(PARTITION BY t.courseid, t.studentid) AS rank
         FROM YOUR_TABLE t)
   DELETE FROM duplicates
    WHERE rank >= 2
   

4. Enable/recreate the primary key