Jenny Zhang wrote: > > I think this is related to my previous question about creating foreign > key. If the referenced column is the primary key, does that > mean sapdb > does a table scan every time it does referential-constraint-check when > it creates foreign key? > > Thanks,
No, why should SAP DB do such thing? The primary key can be checked directly, because it can be found directly because the tree is stored according to the primary key and B*-trees allow the direct access (one page-access per tree-level). Elke SAP Labs Berlin > > > > PRIMARY KEY columns are not indexed in a normal sense. > > The whole primary table is stored according to the primary > key sequence. > > > > If we are talking about referential constraints: > > the referenced column(s) given behind REFERENCES have to be > the PRIMARY KEY of > > the referenced table or they have to be a complete unique > index of that table. > > > > The referencing column(s) (the column(s) from the table for > which you write the > > current create or alter-statement) need not be the primary > key or an unique index. > > For performance reasons (for a delete in the referenced > table) it is a good idea > > to have an index for them (need not be unique), otherwise > the delete has to > > use table scan during referential-constraint-check > (RESTRICT) or -handling > > (SET NULL, SET DELETE, CASCADE). > > > > Elke > > SAP Labs Berlin > > _______________________________________________ > > sapdb.general mailing list > > [EMAIL PROTECTED] > > http://listserv.sap.com/mailman/listinfo/sapdb.general > -- > Jenny Zhang > Open Source Development Lab Inc > 15275 SW Koll Parkway - Suite H > Beaverton, OR 97006 > (503)626-2455 ext 31 > _______________________________________________ sapdb.general mailing list [EMAIL PROTECTED] http://listserv.sap.com/mailman/listinfo/sapdb.general
