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Restores the previous select file.
UN[DO]
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.
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.
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