Re: Join Table

T E Schmitz <mailreg(at)numerixtechnology(dot)de> writes:
> CREATE TABLE SUPPLY
> (
> ITEM_FK integer NOT NULL,
> CONTACT_FK integer NOT NULL,
> COST numeric (7,2),
> PRIMARY KEY (ITEM_FK,CONTACT_FK)
> );

> Question: is it necessary/advisable to create an index for the ITEM_FK
> column? Or is this redundantbecause this column is already one of the PK
> columns?

The PK index will be usable for searches on ITEM_FK alone (though *not*
for searches on CONTACT_FK alone --- a moment's thought about the index
sort order should convince you why). It would be marginally less
efficient for this purpose than a dedicated index on ITEM_FK. But unless
your use of this table is almost all searches and hardly any
modifications, adding a dedicated index is probably a net loss due to
the added update costs.

regards, tom lane