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The CREATE INDEX command is used to create indexes in tables (allows duplicate values)
The 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:
CREATE INDEX idx_lastname
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:
CREATE INDEX idx_pname
ON Persons (LastName, FirstName);
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.