表的多个主键

Question

Hi I'm relatively new to SQL and i am using Microsoft SQL Server

I wish to make a pivot table that links two tables (A and B) together. However the linking is intended to be dynamic. Which means that Links from A to B will be created and removed frequently.

The relationship between A and B is one to many (one A can have many B's)

I want to use a clustered primary key but seem to be unable to make one because the type of the link to A is varchar(max) and the link to B is int.

In Microsoft SQL Server Management Studio i would normally select both columns in the design window and make them both primary keys. However The option is grayed out.

Is there are way to make many different columns of different types a clustered primary key or am i approaching this problem the wrong way?

Answer 1

No, Not possible. PRIMARY means FIRST, MAIN - there can only be one.

You can have an unlimited number (practically) of unique indixes, but only one can ever be the primary key and only one (not necessarily the same one) can be the clustered index.

Now, towards using a varchar(max) in a foreign key relationship - that is the core issue you should fix. SOmeone really f* * * that database design up epically. We can talk about using varchar in general in a key, but varchar(max) is meant for hugh text storage and can not be part of any index (outside a full text index that can not be used in relationships). I would suggest fixing that first.