Wednesday, May 23, 2012

How do UNIQUE indexes work on multiple columns?

just a quick question: how exactly does the unique index check the if the field(s) is(are) unique when added on multiple columns?

For example, if I add a UNIQUE index on the email,password columns, will the index check if:

  1. Is email unique AND is password unique, or

  2. The combination of email,password is unique, as in, it would allow, 123 and, 123

Apologies if my thoughts seem abrupt here, I'm having difficulty in expressing them today for some reason. Thanks in advance!

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