sql - In MySQL does a UNIQUE varchar have to be a PRIMARY KEY as well? -

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i have 2 unique values under 1 table in mysql. 

|id (pk)|varchar(255) unique| ----------------------------- |   1   |      1234abcde    | |   2   |      5678fghij    | |   3   |      9012klmno    |

do have set unique varchar pk or can still use auto_incremented id (int)? or bad practice?

no not need primary key.

additionally: cannot have more 1 'primary key' (different compound primary keys), , makes sense have auto-increment id field convention alone , frameworks (e.g. orm's hibernate , entity framework).

to answer second question, there many business cases many enforce unique constraint on multiple columns without making them primary key - example may have unique, may need able edit/change them:

i.e.

  1. email addresses usernames - forced unique, users need update them
  2. password salts (if generation sound unlikely require enforcement)
  3. random strings used generate one-time or time sensitive links (think bit.ly)

so, point being done time.


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