Question

I want to make a table that simply has two integer columns to serve as a mapping table between two different data sets and I wish to put the correct constraints on it.

I initially set the two columns as a compound primary key, but then realized that represents a many to many, only keeping duplicate many to many mappings from occurring.

How do I specify I want both columns to be unique integers in all rows? I’m using MS SQL, but I suppose this is a general database design question.

Answer 1

Create a Primary Key on one column and another separate unique constraint or unique index, on the other.

CREATE TABLE [dbo].[test](     [x] [int] NOT NULL,     [y] [int] NOT NULL,      CONSTRAINT [PK_test] PRIMARY KEY CLUSTERED       ( [x] ASC)       WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF,           IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON,           ALLOW_PAGE_LOCKS  = ON)       ON [PRIMARY])   ON [PRIMARY]  CREATE UNIQUE NONCLUSTERED INDEX [IX_test] ON [dbo].[test]    ([y] ASC)     WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF,           SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF,           DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS  = ON,           ALLOW_PAGE_LOCKS  = ON)    ON [PRIMARY]