What is Primary index, Cluster Index, Replacement Key, Alternate Key?

The primary index uniquely identifies records in any given table. Each unique combination of Primary Key fields uniquely identifies only one record in the table. There can only be one primary key per table. The cluster Index is the physical order in which records are stored in the table. Cluster Indexes do not have to be unique. Replacement Key - While a surrogate key is great for lookup and database performance, i Alternate Key - A table can have any number of alternate keys. An alternate key may be a natural key or a single field primary key used in foreign or primary key relations with other tables. In either case, to set one, the user must create a new index and then set AllowDuplicates to “No” and AlternateKey to “Yes”. If AllowDuplicates is not set to “No” then AlternateKey should be greyed out and uneditable.