Language Reference

INDEX Statement

indexes a variable in a SAS data set

INDEX variables|NONE

where variables are the names of variables for which indexes are to be built.

You can use the INDEX statement to create an index for the named variables in the current input SAS data set. An index is created for each variable listed if it does not already have an index. Current retrieval is set to the last variable indexed. Subsequent I/O operations such as LIST, READ, FIND, and DELETE can use this index to retrieve observations from the data set if IML determines that indexed retrieval will be faster. The indices are automatically updated when a data set is edited with the APPEND, DELETE, or REPLACE statements. Only one index is in effect at any given time. The SHOW contents command indicates which index is in use.

For example, the following statement creates indexes for the SAS data set CLASS in the order of NAME and the order of SEX:

  
    index name sex;
 

Current retrieval is set to use SEX. A LISTall statement would list females before males.

An INDEX none statement can be used to set retrieval back to physical order.

When a WHERE clause is being processed, IML automatically determines which index to use, if any. The decision is based on the variables and operators involved in the WHERE clause, and the decision criterion is based on the efficiency of retrieval.