SQL CREATE UNIQUE INDEX Keyword
CREATE UNIQUE INDEX
CREATE UNIQUE INDEX command creates a unique index on a table (no duplicate values
Indexes are used to retrieve data from the database very fast. The users cannot see the indexes, they are just used to speed up searches/queries.
The following SQL creates an index named "uidx_pid" on the "PersonID" column in the "Persons" table:
CREATE UNIQUE INDEX uidx_pid
ON Persons (PersonID);
Note: The syntax for creating indexes varies among different databases. Therefore: Check the syntax for creating indexes in your database.
Note: Updating a table with indexes takes more time than updating a table without (because the indexes also need an update). So, only create indexes on columns that will be frequently searched against.