Add extra column after db creation

Lets say I have a db (mysql) that looks like this -

Code:

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Username    Password    DateJoined

Bob        Pass        1/1/2012
Henry      Pass2      2/4/2012
Fred        Pass3      8/5/2012

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But want it to look like this

Code:

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Username    Password    DateJoined    LastLogin

Bob        Pass        1/1/2012      Val1
Henry      Pass2      2/4/2012      Val2
Fred        Pass3      8/5/2012      Val3

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An example^

How would you add in the extra column?

Code:

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ALTER TABLE username ADD LastLogin TEXT NULL;

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Thanks James