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Q: What is a copybook and why is it used?
Answer:
A copybook is a reusable code file that can be included in multiple programs using the COPY statement.
Uses:
- Standard record layouts
- Common working storage definitions
- Reusable paragraphs
- Ensures consistency across programs
Syntax:
COPY EMPREC. COPY EMPREC REPLACING ==EMP== BY ==WS-EMP==.
Benefits:
- Reduces code duplication
- Easier maintenance
- Standard definitions across team
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Q: What is UNLOAD utility?
Answer:
UNLOAD extracts data to sequential file. UNLOAD FROM TABLE name. Output format matches LOAD input. Used for data migration, backup, extract. Can include WHERE clause for filtering.
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Q: What is index-only access?
Answer:
Index-only access retrieves data from index without table access. All needed columns in index (including by include clause). Best performance. EXPLAIN shows INDEXONLY=Y. Design indexes for common queries.
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Q: What is JCLLIB ORDER?
Answer:
JCLLIB ORDER specifies procedure library search order. //JOBNAME JOB ... // JCLLIB ORDER=(PROC.LIB1,PROC.LIB2). Searched for INCLUDE and EXEC procname. Takes precedence over JES2/3 proclibs. Must be before first EXEC statement.
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Q: How to allocate SYSDA?
Answer:
UNIT=SYSDA for disk. Generic device group. Installation defines SYSDA contents. Usually includes all available disk. SMS may direct allocation. UNIT=3390 for specific device type. SYSDA preferred for portability.
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Q: Explain CREATE INDEX
Answer:
CREATE INDEX creates index on table. CREATE INDEX idx ON table(col1, col2). UNIQUE prevents duplicates. CLUSTER determines physical order. Include columns for index-only access. Drop unused indexes for insert performance.
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Q: What is FETCH FIRST?
Answer:
FETCH FIRST n ROWS ONLY limits result set. SELECT * FROM t ORDER BY col FETCH FIRST 10 ROWS ONLY. Optimizes query - doesn't retrieve all. OFFSET for paging. WITH TIES includes equal values.
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Q: What is the purpose of COPY statement?
Answer:
COPY includes copybook members at compile time, promoting code reuse and standardization. Syntax: COPY copybook-name. REPLACING clause allows field substitution. Copybooks typically contain record layouts, working-storage definitions, and common routines.
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Q: Explain EXPORT utility
Answer:
EXPORT creates portable copy with catalog info. IDCAMS EXPORT ds.name OUTFILE(dd). Includes cluster definition. IMPORT recreates on target system. Good for migration.
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Q: Explain FUNCTION LENGTH
Answer:
FUNCTION LENGTH returns byte count. FUNCTION LENGTH(field-name). For group items, includes all subordinates. For variable OCCURS, actual current length. Use in COMPUTE, MOVE, comparisons. Often used with STRING pointer initialization.
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Q: How to use INCLUDE statement?
Answer:
INCLUDE MEMBER=name inserts JCL from JCLLIB member. Processed at conversion time. Can contain any JCL statements. Modular JCL design. INCLUDE can contain INCLUDE. SET statements affect included members.
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Q: Explain DFSORT utility
Answer:
DFSORT sorts/merges files. SYSIN has SORT FIELDS=(1,10,CH,A). SORTIN=input, SORTOUT=output. Options: INCLUDE/OMIT for filtering, OUTREC/INREC for reformatting, SUM for summarization. ICETOOL provides extended functions.
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Q: What is SQLCA structure?
Answer:
SQLCA (SQL Communication Area) contains execution results. SQLCODE for return code. SQLERRM for message. SQLERRD(3) for rows affected. SQLWARN for warnings. INCLUDE SQLCA in WORKING-STORAGE. Check after each SQL statement.