I am not sure as to properly use non-clustered indexes. The SSMS plan estimator said to add another index when the following index was on the table already.
CREATE NONCLUSTERED INDEX [ix_zone_fetch_shipping] ON [dbo].[tbl_shipping_rates_zones] ( [iso] ASC, [mzone] ASC, [postal] ASC ) INCLUDE ( [region], [zone_dom], [zone_emi], [zone_pmi], [zone_fci], [zone_ups], [zone_fed] )
My query was
SELECT * FROM tbl_shipping_rates_zones WHERE postal = '10001'
My question is... should I be creating an index for all possible look up keys? I search by mzone, iso, and postal in different queries.