HP 3000 Manuals HP 3000 Manuals
MERGE Statement The MERGE statement combines two or more identically sequenced files on a set of specified keys. As part of the merge operation, it makes records available in their merged order to an output procedure or an output file. The records are made available following the actual merging of the files. The output procedure or the moving of records to an output file is considered part of the merge process. MERGE statements may appear anywhere within the PROCEDURE DIVISION except in the declaratives portion or in an input or output procedure associated with a SORT or MERGE statement. SyntaxParameters file-name-1 sort/merge file, and is described in a sort/merge file description (SD level) entry in the DATA DIVISION. data-name-1 data items described in records associated with file-name-1. Each may be qualified and may vary in length. None of these data names can be described by an entry either containing an OCCURS clause, or subordinate to an entry containing such a clause. If file-name-1 has more than one record description, then the data items represented by the data names need be described in only one of the record descriptions. alphabet-name either EBCDIC, STANDARD-1, NATIVE, or an alphabet name as defined by you in the SPECIAL-NAMES paragraph of the ENVIRONMENT DIVISION. language-name alphanumeric data item containing the name of the language whose collating sequence should be used. This parameter is an HP extension to the ANSI COBOL standard. language-id integer data item containing the identification number of the language to use. This parameter is an HP extension to the ANSI COBOL standard. file-name-2 files to be merged. These files must not be open at the file-name-3 time the MERGE statement is executed. Each must be a file described in an FD level file description in the DATA DIVISION. No more than one such file name can name a file from a multiple file reel. Any given file name can be used only once in any given MERGE statement. The actual size of the logical record or records described for these files must be equal to the actual size of the logical record or records described for file-name-1. If the data descriptions of the elementary items that make up these records are not identical, it is your responsibility to describe the corresponding records in such a way as to cause an equal number of character positions to be allocated for the corresponding records. procedure-name- name of the first paragraph or section in an output 1 procedure. procedure-name- name of the last paragraph or section in an output 2 procedure. file-name-4 names of output files. These files are subject to the same restrictions as file-name-2. Description The words THROUGH and THRU are equivalent, and can be used interchangeably. The MERGE statement merges all records contained in the files named in the USING phrase. The files to be merged are automatically opened and closed by the merge operation with all implicit functions performed, such as the execution of any associated USE procedures. The files described by file-name-2 and file-name-3 must not be open when the MERGE verb is executed, and may not be opened or closed during an output procedure if one is specified. Following the actual merging of the files, but before they have been closed, the merged records are released in the order in which they were merged. They are released to either the specified output procedure or the specified output file. The results of a merge operation are predictable only when the records in the files to be merged are ordered as described in the ASCENDING or DESCENDING KEY phrase associated with the MERGE statement. The data names following the word KEY are listed from left to right in order of decreasing significance. This decreasing significance is maintained from KEY phrase to KEY phrase. Thus, in the format shown, data-name-1 is the most significant, and each successive data name is the next most significant. When the MERGE statement is executed, the records of file-name-2 and file-name-3 are merged in the specified order (ASCENDING or DESCENDING) using the most significant key data item. Within the records having the same value for the most significant key data item, the records are merged according to the next most significant key data item; this kind of merging continues until all key data items named in the MERGE statement have been used. When the ASCENDING phrase is used, the merged records are in a sequence starting from the lowest value of the key data items and ending with the highest value. When the DESCENDING phrase is used, the merged records are in a sequence from the highest value of the key data item to the lowest. Merging takes place using the rules for comparison of operands of a relation condition. If all corresponding key data items of records to be merged are equal, the records are written to file-name-4, or returned to the output procedure, in the order that the input files are specified in the MERGE statement. COLLATING SEQUENCE Phrase The COLLATING SEQUENCE phrase allows you to specify what collating sequence to use in the merging operation. This phrase is optional. The program collating sequence is used if none is specified in the MERGE statement. See the alphabet clause of the SPECIAL-NAMES paragraph for information on defining and using collating sequences. Refer to the Native Language Support Reference Manual for details about language names and language id's. GIVING and OUTPUT PROCEDURE Phrases You must specify either the GIVING or OUTPUT PROCEDURE phrase in a MERGE statement. If you specify the GIVING phrase, all merged records are automatically written to one or more occurrences of file-name-4. Files named in the GIVING phrase can be sequential, relative, or indexed. If you use the OUTPUT PROCEDURE phrase, there are several rules you must follow in writing the procedure. The procedure must consist of one or more paragraphs or sections that appear contiguously in the source program, and that are not part of any other procedure. Since the RETURN statement is the means of making sorted or merged records available for processing, at least one such statement must appear in the procedure. The procedure may consist of any procedures needed to select, modify, or copy records. The records are returned one at a time in merged order from file-name-1. Control must not be passed to a sort/merge output procedure except during the execution of a SORT or MERGE statement. The procedure itself can contain no SORT or MERGE statements, nor can it contain any explicit transfers of control to points outside its bounds; ALTER, GO TO, and PERFORM statements in the output procedure must refer to procedure names within the bounds of the output procedure. Note that implied transfers of control to declarative procedures are permitted. Thus, for example, a WRITE statement without an AT END phrase is permitted, and will transfer control to some associated declarative procedure if an AT END condition occurs. The remainder of the PROCEDURE DIVISION must not contain any transfers of control to points inside sort/merge output procedures. No ALTER, GO TO, or PERFORM statements outside an output procedure can refer to procedure names within the output procedure. When an output procedure is specified in a MERGE statement, the output procedure is executed as part of the merge operation. The procedure is used after the records have been merged. At compile-time, the compiler inserts a return mechanism at the end of the last section in the output procedure. When this return mechanism is reached, the merge operation is terminated, and control passes to the next executable statement following the MERGE statement. Segmentation Considerations The following restrictions apply to the MERGE statement when it is used in a segmented program. If the MERGE statement appears in a section whose segment number is less than 50, any output procedure named in the MERGE statement must either be totally contained within a segment (or segments) whose segment number (or numbers) is less than 50 or be wholly contained in a single segment whose segment number is greater than 49. If the MERGE statement appears in a section whose segment number is greater than 49, any output procedure referenced by the MERGE statement must either be entirely contained within the same segment or be entirely contained within segments whose segment numbers are less than 50.
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