Home/ Questions/Q 730869
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-14T06:57:40+00:00

I have a (simplified) table consisting of three columns: id INT PRIMARY KEY NOT

  • 0

I have a (simplified) table consisting of three columns:

id INT PRIMARY KEY NOT NULL AUTO_INCREMENT,
foreignID INT NOT NULL,
name VARCHAR NOT NULL

Basically, I would like to add a constraint (at the database level rather than at the application level) where it only possible for one unique ‘name’ to exist per foreignID. For example, given the data (id, foreignid, name):

1,1,Name1
2,1,Name2
3,1,Name3
4,2,Name1
5,2,Name2

I want the constraint to fail if the user tries to insert another ‘Name3’ under foreignId 1, but succeed if the user tries to insert ‘Name3’ under foreignId 2. For this reason I cannot simply make the whole column UNIQUE.

I am having difficulty coming up with a SQL expression to achieve this, can anybody help me?

Thanks

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    Add a unique constraint on (ForeignID, Name). The exact syntax for that depends on your DBMS. For SQL Server:

    CREATE UNIQUE INDEX IndexName ON YourTable (ForeignID, Name)

    (The terms “unique constraint”, “unique key” and “unique index” mean roughly the same.)

    • 0