Does primary key automatically create index

A table can have only primary key whereas there can be multiple unique key on a table.Invocation this statement can be embedded in an application program or issued interactively.We'll go over each one.When you create a new table with a primary key, oracle automatically creates a new index for the primary key columns.All engines including innodb as well as myisam automatically supports the primary key to be indexed.

Does a primary key automatically create an index?Yes a primary key is always an index.One may also ask, do you need to index a primary key?As for constraints, indexes are created for you so that constraint paradigm is setup.Let us create a table with primary key −

You use the key when you want to create an index for a column or a set of columns that is not the part of a primary key or.Clustered indexes are automatically generated if a primary key constraint is defined on a database table.I saw , the primary key utilizes the index even if its non unique.Creating a primary key on a table automatically creates an index on the key.In fact, i had discussed this in another question with regard to primary keys having its own name to distinguish it from other unique (candidate) keys.

Also say there exists two index one on (id, firstname) and other on (id), if i create primary key on (id, firstname), i saw it picked automatically the index which is on (id), which means its also doesn't check the exact match of columns.Thus, it is not necessary to create an index explicitly for primary key columns.