Hi Ted, Any single primary key cannot contain duplicate entries and any single table can have only one primary key. With your example, 'table1.people_id' can have values "1" - "50" and 'table2.location_id' have "1" - "50 at the same time so your final statment is wrong. I assume what the book actually means is that you cannot have, for example, two "1"'s in the same primary key. Trying to insert a new "1" will cause an error. But, if you've chosen it to be auto_increment, then this shouldn't be a problem. Hope that helps. Best wishes, Paul Najman [EMAIL PROTECTED] ----- Original Message ----- From: <[EMAIL PROTECTED]> To: "MySQL List" <[EMAIL PROTECTED]> Sent: Thursday, May 29, 2003 8:19 PM Subject: database newbie
> Ok, since this is THE place for MySQL and related discussion/questions, > here goes: > > I'm trying to understand Keys, I do for the most part, but in reading > the well recommended book 'Database Design for Mere Mortals' I got a > bit confused. > > A check for worthy primary key designation is to ask what fields are > "indirectly" identified by the PK, then the book says to slash such a > field --I suppose later to put it into a separate or subset table; > however, turning the page, the field is there and never removed from > the final version of the book's example table. > (If you have this book it is Chap. 8, pgs. 224-226.) > > Next, again from reading this book, I am told that when i create > Primary Keys manually (or artificially, i.e., not naturally occurring > fields) e.g., making a field called 'table1.people_id' as my Primary > Key (auto-incrementing), and in another table the Primary Key > 'table2.location_id' (auto-incrementing), the book leads me to believe > that each of these *two table's Primary Key's field values cannot be > the same*. > that is, that if the values for the field 'table1.people_id' rows is > "1" - "50", then the field values for 'table2.location_id' (or any > other table) cannot also be "1" - "50". > > Huh??? Is that long winded stuff I just wrote simply wrong? (I think > it is, but need clarity.) *If it is correct, then how is such a thing > accomplished? > > Thanks. > Ted > > > -- > MySQL General Mailing List > For list archives: http://lists.mysql.com/mysql > To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED] > > -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
