UNDO

Discussion

The UNDO command clears the last SUBSET retrieval and returns you to the previous level of data retrieval. Each group of retrieved entries is stored in a temporary internal file known as a select file. Entering the UNDO command removes the last group of retrieved entries (select file) and restores the previous group of retrieved entries as the current select file. The restored select file can be the result of a previous SUBSET, FIND, or MULTIFIND command, but UNDO must follow a SUBSET command. After each SUBSET retrieval, QUERY prints the number of qualified entries retrieved.

Examples

   
Example 1
 
       --> >FIND ALL PERIODICAL.JOURNAL
       |   USING SERIAL READ
       |   60 ENTRIES QUALIFIED
       |   >SUBSET PERIODICAL.JOURNAL = CALIFORNIA
       |   30 ENTRIES QUALIFIED
       --  >UNDO

In this example, the previous 60 entries are in the current select file again.

   
Example 2
 
            >FIND ALL PERIODICAL.JOURNAL
            USING SERIAL READ
            60 ENTRIES QUALIFIED
       --> >SUBSET PERIODICAL.JOURNAL = CALIFORNIA
       |    30 ENTRIES QUALIFIED
       |    >SUBSET PERIODICAL.YEAR = 85
       |    10 ENTRIES QUALIFIED
       ---  >UNDO

In example 2, the previous 30 entries are in the current select file again.