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Q: How does SEARCH ALL differ from SEARCH?
Answer:
SEARCH performs a sequential/linear search from the current index position. SEARCH ALL performs a binary search requiring the table to be sorted (ASCENDING/DESCENDING KEY clause) and indexed. SEARCH ALL is faster for large tables but requires sorted data.
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Q: What is ORGANIZATION clause?
Answer:
ORGANIZATION specifies file structure: SEQUENTIAL (default), INDEXED (VSAM KSDS), RELATIVE (RRDS). Determines access methods available. INDEXED requires RECORD KEY. ACCESS MODE can be SEQUENTIAL, RANDOM, or DYNAMIC.
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Q: How to define KSDS cluster?
Answer:
IDCAMS DEFINE CLUSTER(NAME(ds.name) INDEXED KEYS(len offset) RECORDSIZE(avg max) SHAREOPTIONS(2 3)) DATA(NAME(ds.data) CYLINDERS(5 1)) INDEX(NAME(ds.index) CYLINDERS(1 1)). Keys required for INDEXED.
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Q: How to handle OCCURS INDEXED tables?
Answer:
Indexed tables use INDEXED BY: 05 TBL OCCURS 10 INDEXED BY IDX. SET IDX TO 1 initializes. SET IDX UP BY 1 increments. SEARCH uses index implicitly. More efficient than subscript-index conversion.
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Q: How to define FILE-CONTROL?
Answer:
SELECT file-name ASSIGN TO ddname. ORGANIZATION IS INDEXED. ACCESS MODE IS DYNAMIC. RECORD KEY IS key-field. ALTERNATE RECORD KEY IS alt-key. FILE STATUS IS ws-status. Maps COBOL file to physical dataset.
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Q: How to define and use indexes?
Answer:
INDEX defined with OCCURS: 05 WS-TABLE OCCURS 10 INDEXED BY WS-IDX. SET WS-IDX TO 5 sets position. SET WS-IDX UP/DOWN BY 1 changes position. Use SEARCH verb with index. More efficient than subscripts for table access.
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Q: How to work with OCCURS indexed tables?
Answer:
Define: 01 WS-TABLE. 05 WS-ENTRY OCCURS 100 INDEXED BY WS-IDX. 10 WS-NAME PIC X(20). 10 WS-VALUE PIC 9(5). Access: MOVE WS-NAME(WS-IDX) TO output. Search: SEARCH WS-ENTRY WHEN WS-NAME(WS-IDX) = 'VALUE' perform action.
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Q: Explain ALTERNATE RECORD KEY
Answer:
ALTERNATE RECORD KEY defines secondary indexes for INDEXED files. SELECT file-name ALTERNATE RECORD KEY IS ALT-KEY WITH DUPLICATES. Allows access by multiple keys. DUPLICATES permits non-unique values. Define path in VSAM cluster.
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Q: How to define table with KEY?
Answer:
For binary search, tables need KEY: 05 WS-TABLE OCCURS 100 ASCENDING KEY WS-CODE INDEXED BY WS-IDX. 10 WS-CODE PIC X(5). 10 WS-DESC PIC X(20). SEARCH ALL requires sorted data per KEY. Multiple keys for complex sorts.
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Q: How to define OCCURS ASCENDING?
Answer:
05 TABLE OCCURS 100 ASCENDING KEY IS CODE-FIELD INDEXED BY IDX. 10 CODE-FIELD PIC X(5). 10 DATA-FIELD PIC X(20). ASCENDING means lower values first. Required for SEARCH ALL. DESCENDING also available. Key must be within occurrence.
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Q: How to define ESDS?
Answer:
DEFINE CLUSTER(NAME(ds.name) NONINDEXED RECORDSIZE(avg max)) DATA(NAME(ds.data) CYLINDERS(10 2)). NONINDEXED means ESDS. No KEYS or INDEX components. Access by RBA only.
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Q: What is KEYLEN parameter?
Answer:
KEYLEN specifies key length for new dataset. DCB parameter for VSAM-like. Or VSAM DEFINE CLUSTER KEYS(length offset). Length 1-255. Required for indexed organization. Offset from 0 or 1 depending on context.