Database indexes are data structures that improve the speed of data retrieval operations on a database table at the cost of additional writes and storage space.
Indexes can be created using one or more columns of a database table. These values are kept sorted, thus speeding up searches.
Indexes can be unique or non-unique. Non-unique indexes allow the indexed columns to contain duplicates.
Be aware that while indexes speed up queries they also slow down insertions and updates.
CREATE INDEX <indexname> ON <tablename> (<column>, <column>...);
CREATE UNIQUE INDEX <indexname> ON <tablename> (<column>, <column>...);
DROP INDEX <indexname>;
To specify sort order, the keywords ASC and DESC can be placed after each column name.