ESTIMATE function [Miscellaneous]

Returns selectivity estimates as a percentage calculated by 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 '='.

Returns

REAL

Remarks

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

See also
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;
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