July 22, 2003 at 9:37 am
Hi gurus!
A kinda silly question but what are relationships between tables used for? Can you UPDATE/DELETE rows based on relationships? Do relationships speed up JOINs? Or do you use them only for data integrity?
/Tomi
July 22, 2003 at 9:47 am
Used for data integrity. Not going to make joins faster, indexing is where you get speed - if anything foreignkeys may slow down operations slightly. You can update/delete rows using the CASCADE feature in SQL2K, or you could write some code to figure out the relationships and do the same thing in SQL7.
Andy
July 23, 2003 at 5:23 pm
Creating a data diagram provides the system with information it needs to know the relationships between/among the various tables. It helps the user create constraints, automatically generate triggers, or utilize referential integrity with cascading updates or deletes. For instance, if a table is related to various other tables through a foreign key and the user were to delete the record the system will have enough information to cascade these changes/deletes to all the related records. Vendors generally provide graphical tools, like the data diagrams, to allow the user to enforce integrity. It is a tool to help the user establish and maintain database integrity.
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