Ü  Difference between READE and CHAIN operation

·         The search argument, |search-arg, must be the key or relative record number used to retrieve the record.

·         The CHAIN command does a SETLL and a READE in order to find a match. CHAIN is best used to locate a unique record (like a customer record).

·         SETLL with READE is best used when there can be more than one record found. For example, you can find multiple customer orders in your system for one unique customer.

·         In case of CHAIN, the file operation is used to randomly retrieve a record from a file. The factor 1 value is mandatory for chain operation. The factor 1 value must be key field or RRN.

·         In case of CHAIN the Resulting indicator will be at HI position while in case of READE the indicator will be at LOW position.

·         In case of CHAIN, if the record is found then the pointer will be set, otherwise i.e., if the record does not exist then the pointer will not set. This is the reason why we check with the %Found keyword and moreover after reading the record (in case if the record found and there is more number of records with the same keyword).

·         We cannot move to another record, which meets the same criteria specified in the Chain operation. So the conclusion is we cannot read more number of records with the Chain operation, if there are more number of records exists with the same criteria in the file.

·         Whereas using READE, we can read all the records which meet the same criteria using subsequent READE operation. If there are no records with the specified criteria then the pointer will be set to EOF.

·         In case the program uses a SETLL / READE type loop to look for a particular record it needed. However, once it is found the record it carries the processing of the loop until the end of the file.



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