Alternate Key
It is commonplace in SQL databases to declare a single primary key, the most important unique key. However, there could be further unique keys that could serve the same purpose. These should be marked as 'unique' keys. This is done to prevent incorrect data from entering a table (a duplicate entry is not valid in a unique column) and to make the database more complete and useful. These could be called alternate keys.
Read more about this topic: Unique Key
Famous quotes containing the words alternate and/or key:
“Strange, that some of us, with quick alternate vision, see beyond our infatuations, and even while we rave on the heights, behold the wide plain where our persistent self pauses and awaits us.”
—George Eliot [Mary Ann (or Marian)
“Power, in Case’s world, meant corporate power. The zaibatsus, the multinationals ..., had ... attained a kind of immortality. You couldn’t kill a zaibatsu by assassinating a dozen key executives; there were others waiting to step up the ladder; assume the vacated position, access the vast banks of corporate memory.”
—William Gibson (b. 1948)