IDXNAME= Data Set Option

Directs SAS to use a specific index to match the conditions of a WHERE expression.

Valid in:	DATA and PROC steps
Category:	User Control of SAS Index Usage
Restrictions:	Use with input data sets only.
Restrictions:	Mutually exclusive with IDXWHERE= data set option.
Supports:	SAS data set

Syntax

Syntax

IDXNAME=index-name

Syntax Description

index-name

specifies the name (up to 32 characters) of a simple or composite index for the SAS data set. SAS does not attempt to determine whether the specified index is the best one or if a sequential search might be more resource efficient.

Interaction

The specification is not a permanent attribute of the data set and is valid only for the current use of the data set.

Details

By default, to satisfy the conditions of a WHERE expression for an indexed SAS data set, SAS identifies zero or more candidate indexes that could be used to optimize the WHERE expression. From the list of candidate indexes, SAS selects the one that it determines will provide the best performance, or rejects all of the indexes if a sequential pass of the data is expected to be more efficient.

Because the index that SAS selects might not always provide the best optimization, you can direct SAS to use one of the candidate indexes by specifying the IDXNAME= data set option. If you specify an index that SAS does not identify as a candidate index, then IDXNAME= does not process the request. That is, IDXNAME= does not allow you to specify an index that would produce incorrect results.

Comparisons

IDXWHERE= enables you to override the SAS decision about whether to use an index.

Example: Specifying an Index for a WHERE Expression

This example uses the IDXNAME= data set option in order to direct SAS to use a specific index to optimize the WHERE expression. SAS then disregards the possibility that a sequential search of the data set might be more resource efficient and does not attempt to determine whether the specified index is the best one. (Note that the EmpNum index was not created with the NOMISS option.)

data mydata.empnew;
   set mydata.employee (idxname=empnum);
   where empnum < 2000;
run;