SQL CREATE INDEX Keyword
CREATE INDEX command is used to
create indexes in tables (allows 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 "idx_lastname" on the "LastName" column in the "Persons" table:
ON Persons (LastName);
If you want to create an index on a combination of columns, you can list the column names within the parentheses, separated by commas:
ON Persons (LastName, FirstName);
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.