David, Not bang on. A foreign key is a key which is the value of a key from a 'parent' table. In MySQL, if the table and its parent are InnoDB, the db will prevent you from editing the parent key 'out of sync' as you say.
PB ----- > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > Hi again, all -- > > I apologize in advance for asking kindergarten-level questions on the > list, but my head is getting really bruised from this one. I'm trying to > understand what makes a relational (not necessarily transactional) > database and how, in what forms, MySQL is that. > > It's my understanding that to truly be relational a column in one table > (let's say "sales") must get its value from a column in another table > (let's say "customers") rather than just having the same name. That is, > it would be easy for anything to have > > +------------------------+ +------------------------+ > | SALES | | CUSTOMERS | > +---------+-------+------+ +------+-----------------+ > | product | price | cust | | num | name | > +---------+-------+------+ +------+-----------------+ > | TXLblue | 14.99 | 1136 | | 1136 | richard roe | > +---------+-------+------+ +------+-----------------+ > | CMMblck | 11.50 | 2408 | | 2408 | jane doe | > +---------+-------+------+ +------+-----------------+ > | SMMblue | 22.75 | 2408 | | 8421 | bob smith | > +---------+-------+------+ +------+-----------------+ > > where SALES.cust gets filled with the same value as CUSTOMERS.num -- but > should the customer number somehow change we're now out of sync, whereas > in a truly relational database the fields in the SALES.cust column would > *be* the fields in the CUSTOMERS.num column rather than simply having the > same value. > > Am I lost, out of my tree, confused, or bang on? And how (perhaps InnoDB > tables) does MySQL support this if I'm not any of the first three? > > > TIA & HAND > > mysql query, > :-D > - -- > David T-G * There is too much animal courage in > (play) [EMAIL PROTECTED] * society and not sufficient moral courage. > (work) [EMAIL PROTECTED] -- Mary Baker Eddy, "Science and Health" > http://www.justpickone.org/davidtg/ Shpx gur Pbzzhavpngvbaf Qrprapl Npg! > > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v1.0.7 (FreeBSD) > > iD8DBQE97SO3Gb7uCXufRwARAooDAKDI6dhugjyejLAEwC5Sjl6Pjqz/nACcDoj0 > vUcEuhNZHvTYh+KjGz05/9Q= > =hZrX > -----END PGP SIGNATURE----- > > --------------------------------------------------------------------- > 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 > > --------------------------------------------------------------------- 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
