On 02/03/2018 01:10 , Daevor The Devoted wrote:
On Fri, Mar 2, 2018 at 12:05 AM, Gavin Flower <gavinflo...@archidevsys.co.nz <mailto:gavinflo...@archidevsys.co.nz>> wrote:On 02/03/18 06:47, Daevor The Devoted wrote: On Thu, Mar 1, 2018 at 2:07 PM, Rakesh Kumar <rakeshkumar...@aol.com <mailto:rakeshkumar...@aol.com> <mailto:rakeshkumar...@aol.com <mailto:rakeshkumar...@aol.com>>> wrote: >Adding a surrogate key to such a table just adds overhead, although that could be useful >in case specific rows need updating or deleting without also modifying the other rows with >that same data - normally, only insertions and selections happen on such tables though, >and updates or deletes are absolutely forbidden - corrections happen by inserting rows with >an opposite transaction. I routinely add surrogate keys like serial col to a table already having a nice candidate keys to make it easy to join tables. SQL starts looking ungainly when you have a 3 col primary key and need to join it with child tables. I was always of the opinion that a mandatory surrogate key (as you describe) is good practice. Sure there may be a unique key according to business logic (which may be consist of those "ungainly" multiple columns), but guess what, business logic changes, and then you're screwed! So using a primary key whose sole purpose is to be a primary key makes perfect sense to me. I once worked in a data base that had primary keys of at least 4 columns, all character fields, Primary Key could easily exceed 45 characters. Parent child structure was at least 4 deep. A child table only needs to know its parent, so there is no logical need to include its parent and higher tables primary keys, and then have to add a field to make the composite primary key unique! So if every table has int (or long) primary keys, then a child only need a single field to reference its parent. Some apparently safe Natural Keys might change unexpectedly. A few years aback there was a long thread on Natural versus Surrogate keys - plenty of examples were using Natural Keys can give grief when they had to be changed! I think it best to isolate a database from external changes as much as is practicable. Surrogate keys also simply coding, be it in SQL or Java, or whatever language is flavour of the month. Also it makes setting up testdata and debugging easier. I almost invariably define a Surrogate key when I design tables. Cheers, GavinThank you! I think you have expressed far more clearly what I have been trying to say. +10 to you.
Me too. Another +10. --- El software de antivirus Avast ha analizado este correo electrónico en busca de virus. https://www.avast.com/antivirus
