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In databases, a partial index, also known as filtered index is an index which has some condition applied to it so that it includes a subset of rows in the table.

This allows the index to remain small, even though the table may be rather large, and have extreme selectivity.

Suppose you have a transaction table where entries start out with STATUS = 'A' , and then may pass through other statuses before reaching a final status, 'F', at which point it is no longer likely to be processed again.

In PostgreSQL, a useful partial index might be defined as:

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