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Overview
statement is used to create indexes on tables in databases, to speed up data retrieval.
Formula
The users cannot see the indexes, they are just used to speed up searches/queries.Updating tables with indexes are more time-consuming than tables without indexes (because the indexes must also be updated). So, only create indexes on columns that are frequently searched against.
There are two types of indexes:
Formula
- Creates a non - unique index (duplicate values are allowed)index_name ON table_name (
column1, column2, ...);index_name ON table_name (
column1, column2, ...);The syntax for creating indexes varies among different databases. Check the syntax for creating indexes in your database!
Formula
The following SQL creates a non - unique 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_lname_fname
ON Persons (LastName, FirstName);statement is used to remove an index.
table_name. index_name
;table_name
index_name
;index_name ON table_name
;index_name
;