Convert Unix timestamp into human readable date using MySQL

Use FROM_UNIXTIME():

SELECT
  FROM_UNIXTIME(timestamp) 
FROM 
  your_table;

See also: MySQL documentation on FROM_UNIXTIME().

Why bother saving the field as readable? Just us AS

SELECT theTimeStamp, FROM_UNIXTIME(theTimeStamp) AS readableDate
               FROM theTable
               WHERE theTable.theField = theValue;

EDIT: Sorry, we store everything in milliseconds not seconds. Fixed it.