CREATE INDEX
Description
Use the CREATE INDEX statement to create an index in the specified table.
Syntax
CREATE [ REVERSE ] [ UNIQUE ] INDEX [ index_name ]
ON table_name ( column_name[(prefix_length)] [ASC | DESC] [ {, column_name[(prefix_length)] [ASC | DESC]} ...] ) [ ; ]
- REVERSE : Creates an index in the reverse order. A reverse index helps to increase sorting speed in descending order.
- UNIQUE : Creates an index with unique values.
- index_name : Specifies the name of the index to be created. The index name must be unique in the table. If omitted, a name is automatically assigned.
- prefix_length : When you specify an index for character- or bit string-type column, you can create an index by specifying the beginning part of the column name as a prefix. You can specify the length of the prefix in bytes in parentheses next to the column name. You cannot specify prefix_length in a multiple column index or a UNIQUE index. It is impossible to create an index by specifying prefix_length as a host variable. If you want to guarantee the query result order in the index in which prefix_length is specified, you must specify the ORDER BY clause.
- table_name : Specifies the name of the table where the index is to be created.
- column_name : Specifies the name of the column where the index is to be applied. To create a composite index, specify two or more column names.
- ASC | DESC : Specifies the sorting order of columns. In case of a REVERSE index, ASC is ignored and DESC is applied.
Example 1
The following example shows how to create a reverse index.
CREATE REVERSE INDEX gold_index ON participant(gold);
Example 2
The following example shows how to create a multiple column index.
CREATE INDEX name_nation_idx ON athlete(name, nation_code);
Example 3
The following example shows how to create a single column index. In this example, 1-byte long prefix is specified for the nation_code column when creating an index.
CREATE INDEX ON game(nation_code(1));
CREATE INDEX game_date_idx ON game(game_date);