ESTIMATE function [Miscellaneous]

Provides selectivity estimates for the query optimizer, based on specified parameters.

Syntax

ESTIMATE( column-name [, value  [, relation-string ] ] )

Parameters

column-name The column used in the estimate.
value The value to which the column is compared. The default is NULL.
relation-string The comparison operator used for the comparison, enclosed in single quotes. Possible values for this parameter are: =, >, <, >= , <=, <>, !=, !<, and !>. The default is =.

Remarks

If value is NULL then the relation strings '=' and '!=' are interpreted as the IS NULL and IS NOT NULL conditions, respectively.

Standards and compatibility

SQL/2003 Vendor extension.

Example

The following statement returns the percentage of EmployeeID values estimated to be greater than 200. The precise value depends on the actions you have carried out on the database.

SELECT FIRST ESTIMATE( EmployeeID, 200, '>' )
   FROM Employees
   ORDER BY 1;