CREATE INDEX Statement

Description

Creates a new index on an existing table.

Note

For non-Jet databases, the Microsoft Jet database engine doesn't support the use of CREATE INDEX (except to create a pseudo index on an ODBC attached table) or any of the data definition language (DDL) statements. Use the data access object Create methods instead. For more information, see the Remarks section.

Syntax

CREATE [ UNIQUE ] INDEX index
ON table (field [ASC | DESC ][, field [ASC | DESC ], ...])
[WITH { PRIMARY | DISALLOW NULL | IGNORE NULL }]

The CREATE INDEX statement has these parts.

Part	Description

index	The name of the index to be created.
table	The name of the existing table the index will be created on.
field	The name of the field or fields to be indexed. To create a single-field index, list the field name in parentheses following the table name. To create a multiple-field index, list the name of each field to be included in the index. To create descending indexes, use the DESC reserved word; otherwise, indexes are assumed to be ascending.

Remarks

To prohibit duplicate values in the indexed field or fields of different records, use the UNIQUE reserved word.

In the optional WITH clause, you can enforce data validation rules. You can:

Prohibit Null entries in the indexed field or fields of new records by using the DISALLOW NULL option.
Prevent records with Null values in the indexed field or fields from being included in the index by using the IGNORE NULL option.
Designate the indexed field or fields as the primary key by using the PRIMARY reserved word. This implies that the key is unique, so you can omit the UNIQUE reserved word.

You can use CREATE INDEX to create a pseudo index on an attached table in an ODBC data source such as SQL Server that does not already have an index. You don't need permission or access to the remote server to create a pseudo index, and the remote database is unaware of and unaffected by the pseudo index. You use the same syntax for attached and native tables. This can be especially useful to create an index on a table that would ordinarily be read-only due to lack of an index.

You can also use the ALTER TABLE statement to add a single- or multiple-field index to a table, and you can use the ALTER TABLE statement or the DROP statement to remove an index created with ALTER TABLE or CREATE INDEX.

Note

Don't use the PRIMARY reserved word when you create a new index on a table that already has a primary key; if you do, an error occurs.

See Also

ALTER TABLE Statement, CONSTRAINT Clause, CREATE TABLE Statement, DROP Statement.

Example

This example creates an index consisting of the fields Home Phone and Extension in the Employees table.

CREATE INDEX NewIndex ON Employees (HomePhone, Extension);

This example creates an index on the Employees table using the Social Security Number field. No two records can have the same data in the SSN field, and no Null values are allowed.

CREATE UNIQUE INDEX CustID ON Customers (CustomerID) WITH DISALLOW NULL;

This example creates an index on a hypothetical ODBC linked table. The table's remote database is unaware of and unaffected by the new index.

CREATE UNIQUE INDEX OrderID ON OrderDetails (OrderID);