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Unanswered: About index in SQL
Can somebody explain what index do exactly???
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provides a shortcut to the rows you want
Originally Posted by
let's assume you walk into the empire state building looking for gadget company
all you see is a directory listing the companies on each floor --
1st floor -- widgets r us, gizmos inc, doohickey company
2nd floor -- thingamajig enterprises, whatsis inc, gewgaw internationsl
3rd floor -- ... you get the idea
what you have to do is scan (read sequentially) every floor in the directory until you find the company you're looking for
it would be even worse if there was no directory at all, and you had to actually visit each floor to see if gadget company was there
on the other hand, suppose you had a building directory which listed the companies in alphabetic order
you just look at the list under "G" to find the floor that gadget company is on, and go straight to that floor
that's an index -- it gives the database a shortcut to the rows you asked for