> Hi I'm relatively new to MySQL though I familiar to other simple > databases. Ahem... [takes Sumarlidi aside and explains very carefully how the MySQL developers feel about hearing MySQL being called a "simple database" ;-) ] > I have been reading the manual but not doing well understanding > the function > of auto_increment and Premier Key. > > Lets say I have a table with a few columns. One of them is an ID with > auto_increment. It has 1000 rows. If I delete row #500 to #599 (total of > 100), will the MySQL update the ID value for row #600 to #1000, No. > or will it stay as it was? Yes. The whole point of having such a column is to create and maintain a unique identifier for the record for as long as it lives. > If it stays as it was, and afterwards when I add a row (or > record), will it > continue from row #1001 or will it use the value from #500 to #599? #1001 (same argument -- you don't want something you thought was dead and gone to seemingly reappearing all of a sudden) > > What is the Primary Key used for and how does it work? Do I need it if I > have a row ID like mentioned above? In most cases, this is the primary function of the primary key. The primary key is unique in a couple of respects: 1) it is always declared as NOT NULL UNIQUE, meaning that you're ensured that for any record there is always a well-defined, distinct ID as you must always declare it (or have MySQL do it for you through auto_increment) and you can never assign the same value to two different rows; You may have other UNIQUE indexes; however, there are some subtle differences between these and a primary key. errrr... hmmmm... I'm sure there are. Though for the life of me, I can't think of any off the top of my head right now. I'll go get some coffee while someone else explains this to you. / Carsten -- Carsten H. Pedersen keeper and maintainer of the bitbybit.dk MySQL FAQ http://www.bitbybit.dk/mysqlfaq --------------------------------------------------------------------- Before posting, please check: http://www.mysql.com/manual.php (the manual) http://lists.mysql.com/ (the list archive) To request this thread, e-mail <[EMAIL PROTECTED]> To unsubscribe, e-mail <[EMAIL PROTECTED]> Trouble unsubscribing? Try: http://lists.mysql.com/php/unsubscribe.php
