A key is a set of columns or expressions on which you can build an index.

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Although the terms are often used interchangeably, indexes and keys are different. Indexes are structures stored in the database that users manage using SQL statements. Keys are strictly a logical concept.

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The following statement creates an index on the customer_id column of the sample table oe.orders:

CopyCREATE INDEX ord_customer_ix ON orders (customer_id);

In the preceding statement, the customer_id column is the index key. The index itself is named ord_customer_ix.

Note

Primary and unique keys automatically have indexes, but you might want to create an index on a foreign key.

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See also

• “Data Integrity”
• Oracle Database SQL Language Reference CREATE INDEX syntax and semantics

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