1. Some SQL implementations includes data de nition commands to create and drop indices. The IBM SAA-SQL commands are

• An index is created by

create index <index-name>
on r (<attribute-list>)

• The attribute list is the list of attributes in relation r that form the search key for the index.
• To create an index on bname for the branch relation:

create index b-index
on branch (bname)

 If the search key is a candidate key, we add the word unique to the de nition:

create unique index b-index
on branch (bname)

• If bname is not a candidate key, an error message will appear.
• If the index creation succeeds, any attempt to insert a tuple violating this requirement will fail.
• The unique keyword is redundant if primary keys have been de ned with integrity constraints already.

2. To remove an index, the command is

drop index <index-name>