COBOL Manual for TNS/E Programs (H06.08+, J06.03+)

Usage Considerations:
• Placement of MERGE Statements
A MERGE statement cannot appear in the Declaratives Portion of the Procedure Division.
• Files Specified in the MERGE Statement
You can merge to and from these types of files:
◦ Disk files
◦ Blocked tape files
◦ Multiple-reel tape files
◦ Tape files on a multiple-file reel
The files specified in the MERGE statement are subject to these restrictions:
◦ Every file record must contain all of the key fields.
◦ A file name cannot appear more than once in the same MERGE statement.
◦ Two files of a multiple-file tape reel cannot appear in the same MERGE statement.
◦ Files that appear in the same MERGE statement cannot appear in a SAME AREA or SAME
SORT-MERGE AREA clause.
◦ Except for merge-out files, files that appear in the same MERGE statement cannot
appear in the SAME RECORD AREA clause.
◦ A merge-in-1, merge-in-2, or merge-in-n file whose SELECT clause includes the
OPTIONAL phrase must be present at execution time.
• Merge Keys
Each merge key is subject to these restrictions:
◦ The data item specified by key must be described within a record associated with
merge-file. When merge-file has more than one record description entry, a merge
key data item can be defined within any one of those entries.
◦ No key can have an OCCURS clause or be subordinate to an item that has an OCCURS
clause.
◦ No key can have a variable size (that is, have an OCCURS DEPENDING clause in the
description of a subordinate item).
Keys are listed from left to right within the MERGE statement in order of decreasing significance
(that is, the first key is the most significant and the last key is the least significant).
ASCENDING and DESCENDING phrases do not affect keys’ significance.
When a key is in an ASCENDING phrase, the merged sequence is from the record with the
lowest value in the key to the record with the highest value. When a key is in a DESCENDING
phrase, the merged sequence is from the record with the highest value in the key to the record
with the lowest value. In both cases, the rules for comparison of operands in a relation condition
determine which value is higher.
The results of the merge operation are predictable only when the records in each of the input
files are ordered as described in the key-specifier phrases.
The PROGRAM COLLATING SEQUENCE clause affects merge operations.
364 Procedure Division Verbs