2种独特的字段组合，反之亦然

Question

Hello is it possible to have a combination of 2 fields vice versa ?

Example:

ID  catID
 1    58 

So that we couldnt store another row as 58-1. Currently I have primary key on both fields, but it allows me to store 58-1 combination.

thanks

Answer 1

You would combine the two fields using concat() :

select concat(id, '-', catId) as CombinedId
from t;

You can encapsulate this in a view, if you like.

You can use CombinedId to join to another table, if you like.

However, this isn't recommended. If you want to compare, than use the two values independently.

Answer 2

Assuming ID and catID are symmetrical ¹ , you could simply:

CHECK (ID < catID)

Or possibly (depending on your requirements):

CHECK (ID <= catID)

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¹ Ie (ID = X, catID = Y) is equivalent to (ID = Y, catID = X) for every X and Y .