How to cross join 2 columns of the same field in 1 table?

Question

MySQL

There is a table of correspondence of friends
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idUser | IdfriendUser | dateadd |
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1 | 2 | date |
2 | 3 | date |
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how to get a table that duplicates a friend's field in a user field and a field user in friend field
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idUser | IdfriendUser | dateadd |
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1 | 2 | date |
2 | 1 | date |
2 | 3 | date |
3 | 2 | date |
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and is it even worth doing it this way?

Answer 1

Whether or not you need to decide. In principle, it can be convenient for various associations.
You can hang on the table triggers for adding and deleting records that will add or delete a mirror record.

Answer 2

And why do you need it?
Try cross join

Answer 3

Better tell me what task, maybe you don't need it.