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Q: How do I fix S0C7 Data Exception ABEND?
Answer:
S0C7 occurs when the program tries to perform arithmetic on non-numeric data.
Common Causes:
- Uninitialized numeric fields (contains spaces/garbage)
- Moving alphanumeric data to numeric field
- Reading file with wrong record layout
- Array subscript accessing wrong memory
How to Fix:
- Initialize all numeric fields to ZEROS
- Validate input before arithmetic
- Check file layouts match
- Use DISPLAY to debug field contents
* Always initialize
INITIALIZE WS-RECORD.
MOVE ZEROS TO WS-AMOUNT.
* Validate before use
IF WS-INPUT IS NUMERIC
COMPUTE WS-RESULT = WS-INPUT * 2
END-IF.
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Q: What is the difference between KSDS and ESDS?
Answer:
KSDS (Key Sequenced Data Set):
- Records accessed by unique key
- Records stored in key sequence
- Has both data and index components
- Supports random and sequential access
- Can delete and reinsert records
- Most commonly used VSAM type
ESDS (Entry Sequenced Data Set):
- Records stored in arrival order
- Accessed by RBA (Relative Byte Address)
- No index component
- Cannot delete records (only mark inactive)
- Similar to sequential files
- Good for logs, audit trails
Use KSDS when: You need key-based access, updates, deletes
Use ESDS when: Sequential processing only, append-only data
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Q: Explain REDEFINES clause with an example.
Answer:
REDEFINES allows the same storage area to be referenced by different data names with different definitions.
Rules:
- Must be at same level as item being redefined
- Cannot redefine item with OCCURS
- Redefined item must appear first
- Lengths should match or redefining should be shorter
01 WS-DATE. 05 WS-DATE-NUM PIC 9(8). 01 WS-DATE-X REDEFINES WS-DATE. 05 WS-YEAR PIC 9(4). 05 WS-MONTH PIC 9(2). 05 WS-DAY PIC 9(2).
Same 8 bytes can be accessed as single number or individual components.
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Q: How to handle SQLCODE -805?
Answer:
-805 is DBRM or package not found. Plan bound but package missing or invalidated. REBIND PACKAGE. Check collection, package name. Verify BIND completed successfully. May need BIND PLAN to add package.
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Q: What is the difference between PARM and SYSIN for passing parameters?
Answer:
PARM (EXEC statement):
- Limited to 100 characters
- Passed in memory to program
- Accessed via LINKAGE SECTION
- Good for small, simple parameters
SYSIN (DD statement):
- No practical size limit
- Read as a file by program
- Can contain multiple records
- Good for control cards, complex input
// PARM example //STEP1 EXEC PGM=MYPROG,PARM='PARAM1,PARAM2' // SYSIN example //SYSIN DD * CONTROL OPTION1 DATE=20231215 LIMIT=1000 /*
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Q: How to tune DB2 queries?
Answer:
Check EXPLAIN output. Look at: access type (index vs scan), join method, sort operations. Add indexes for predicates. Rewrite with hints. Update statistics. Check for full tablespace scans. Monitor actual execution.
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Q: Explain REDEFINES clause usage
Answer:
REDEFINES allows multiple data descriptions for same memory. 01 WS-DATE PIC 9(8). 01 WS-DATE-R REDEFINES WS-DATE. 05 WS-YEAR PIC 9(4). 05 WS-MONTH PIC 99. 05 WS-DAY PIC 99. Cannot redefine with larger size. Useful for different views of data.
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Q: Explain VIEW creation
Answer:
VIEW is saved query. CREATE VIEW name AS SELECT... WITH CHECK OPTION enforces WHERE on updates. Can be updatable if simple. Views for security, simplification. Materialized views (MQT) store data.
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Q: What is MQT?
Answer:
MQT (Materialized Query Table) stores computed results. CREATE TABLE name AS (SELECT...) DATA INITIALLY DEFERRED REFRESH DEFERRED. Improves query performance. REFRESH TABLE updates. Use for aggregations, joins.
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Q: How to handle -551 SQLCODE?
Answer:
-551 is authorization failure. No privilege for operation. Check GRANT statements. May need SELECT, UPDATE, DELETE, INSERT authority. GRANT privilege ON object TO user/role. Check SYSIBM.SYSTABAUTH.
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Q: What is GRANT and REVOKE?
Answer:
GRANT gives privileges: GRANT SELECT ON table TO user. REVOKE removes: REVOKE SELECT ON table FROM user. Privileges: SELECT, INSERT, UPDATE, DELETE, EXECUTE. WITH GRANT OPTION allows re-granting. Essential for security.
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Q: How to handle SQLCODE 100?
Answer:
SQLCODE 100 means not found or end of data. For SELECT INTO: no matching row. For FETCH: no more rows. For UPDATE/DELETE: no rows affected. Check context - may be normal condition, not error.
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Q: What is alternate index?
Answer:
AIX provides secondary access path. DEFINE AIX over base cluster. Different key. DEFINE PATH to access. BLDINDEX populates. UPGRADE option maintains AIX on base updates. Multiple AIX per cluster.
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Q: How to update KSDS record?
Answer:
READ record (optionally FOR UPDATE). Modify record area. REWRITE record. Key cannot change on REWRITE. Status 00 if successful. ACCESS MODE must allow updates.
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Q: How to use FUNCTION CURRENT-DATE?
Answer:
FUNCTION CURRENT-DATE returns 21-char timestamp. Format: YYYYMMDDHHMMSSDHHMM (D=hundredths, HH=GMT offset). MOVE FUNCTION CURRENT-DATE TO WS-TIMESTAMP. Parse components with reference modification or REDEFINES.
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Q: Explain UPGRADE path AIX?
Answer:
UPGRADE AIX maintained automatically on base cluster changes. PATH allows access but not update. PATH with UPDATE allows updates via alternate key. UPGRADE adds overhead but keeps AIX current.
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Q: What is EXEC CICS READ?
Answer:
READ retrieves VSAM record. EXEC CICS READ FILE(name) INTO(area) RIDFLD(key) LENGTH(len). Optionally: UPDATE for update intent, KEYLENGTH for partial key. Generic key with GENERIC/KEYLENGTH. Returns NOTFND if missing.
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Q: What is EIB?
Answer:
EIB (Execute Interface Block) contains execution info. EIBCALEN=COMMAREA length. EIBTRNID=transaction. EIBAID=attention key. EIBDATE/EIBTIME=date/time. EIBRESP/EIBRESP2=response codes. Automatically available in COBOL.
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Q: How to use SET statement?
Answer:
SET symbol=value assigns value. SET DATE=&LYYMMDD (system symbol). Multiple: SET A=1,B=2. Scope: job/proc. Override on EXEC. SET can reference other symbols. Evaluated at conversion time. Enables parameter files.
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Q: How to SYNCPOINT?
Answer:
SYNCPOINT commits changes. EXEC CICS SYNCPOINT. Makes updates permanent. Or SYNCPOINT ROLLBACK undoes since last sync. Implicit syncpoint at task end. Use for transaction consistency.
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Q: Explain ASKTIME/FORMATTIME
Answer:
ASKTIME gets current time. EXEC CICS ASKTIME ABSTIME(ws-abstime). FORMATTIME converts to readable. FORMATTIME ABSTIME(ws-abstime) DATESEP('/') TIMESEP(':'). Formatting options available.
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Q: How to WRITEQ with REWRITE?
Answer:
WRITEQ TS with REWRITE updates existing item. EXEC CICS WRITEQ TS QUEUE(name) FROM(data) REWRITE ITEM(n). Without REWRITE, adds new item. ITEM must exist for REWRITE.
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Q: How to handle DUPKEY?
Answer:
DUPKEY on WRITE means key exists. Check: IF ws-resp = DFHRESP(DUPKEY). Handle appropriately - maybe update instead. Or error to user. Common for insert logic.
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Q: Explain DATAONLY option
Answer:
DATAONLY sends only changed data. EXEC CICS SEND MAP DATAONLY FROM(data). No map formatting. Faster for updates. Fields must exist on screen. Use after initial MAPONLY.
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Q: What is RUNSTATS and when to use it?
Answer:
RUNSTATS collects table/index statistics for optimizer. Run after significant data changes (loads, deletes). Updates catalog tables (SYSTABLES, SYSINDEXES). Optimizer uses for access path selection. RUNSTATS TABLESPACE db.ts INDEX(ALL).
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Q: What is CURRENT DATE function?
Answer:
CURRENT DATE returns today's date. CURRENT TIME for time. CURRENT TIMESTAMP for both. No parentheses needed. Used in SELECT, WHERE, INSERT. Can compare: WHERE hire_date > CURRENT DATE - 30 DAYS.
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Q: How to handle date arithmetic?
Answer:
DATE + n DAYS adds days. DATE - n MONTHS subtracts months. DAYS(date2) - DAYS(date1) gives day count. DATEDIFF function available. TIMESTAMPDIFF for time differences. DATE/TIME functions for extraction.
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Q: What is clustered index?
Answer:
Clustered index determines physical row order. Only one per table. Other indexes are secondary. CLUSTER keyword on CREATE INDEX. Good for range queries on cluster key. REORG restores clustering after updates.
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Q: What is BETWEEN operator?
Answer:
BETWEEN tests range inclusively. WHERE col BETWEEN 1 AND 100. Equivalent to col >= 1 AND col <= 100. Works with dates, times. Can use NOT BETWEEN for exclusion. Index can be used for BETWEEN.
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Q: Explain UPDATE with JOIN
Answer:
UPDATE table SET col = value FROM table t1 INNER JOIN table t2 ON... WHERE condition. Or: UPDATE t1 SET col = (SELECT col FROM t2 WHERE t2.key = t1.key). Merge statement is alternative.
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Q: Explain DB2 triggers
Answer:
Trigger fires automatically on INSERT/UPDATE/DELETE. CREATE TRIGGER name AFTER/BEFORE/INSTEAD OF event ON table FOR EACH ROW/STATEMENT. Use for audit, validation, derived columns. Can impact performance.
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Q: What is CHECK utility?
Answer:
CHECK validates data integrity. CHECK DATA TABLESPACE db.ts. Finds constraint violations, orphan rows. CHECK INDEX validates index structure. CHECK LOB for LOB issues. Run periodically or after issues.
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Q: Explain partitioning strategies
Answer:
Range partitioning by value ranges (date, key ranges). Hash partitioning distributes evenly. Partition independence allows parallel operations. Partition pruning improves queries. Rotate partitions for time-series.
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Q: What is REBIND and when needed?
Answer:
REBIND updates access path without precompile. REBIND PACKAGE after RUNSTATS, index changes. REBIND PLAN for plan-level changes. Can improve or degrade performance - test first. EXPLAIN before/after.
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Q: How does ACCEPT and DISPLAY work?
Answer:
ACCEPT reads from console/system: ACCEPT WS-DATE FROM DATE, ACCEPT WS-INPUT FROM CONSOLE. DISPLAY writes to console: DISPLAY 'Message' WS-FIELD. UPON clause specifies destination. Limited in batch; mainly for debugging or simple interaction.
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Q: How to prevent SQL injection?
Answer:
Use parameter markers (?), not concatenation. PREPARE stmt FROM 'SELECT * FROM t WHERE c = ?'. EXECUTE stmt USING :hostvar. Never build SQL with user input directly. Validate input. Use static SQL when possible.
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Q: How to use intrinsic functions?
Answer:
COBOL-85 intrinsic functions: FUNCTION LENGTH(field), FUNCTION CURRENT-DATE, FUNCTION UPPER-CASE(field), FUNCTION NUMVAL(field), FUNCTION MOD(a,b), FUNCTION INTEGER-OF-DATE(date). Use in expressions or with COMPUTE. Return values only, no side effects.
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Q: What is OPEN mode options?
Answer:
OPEN INPUT for read, OUTPUT for write (creates), I-O for read/update, EXTEND for append. Multiple files per OPEN. OPEN OUTPUT deletes existing file! EXTEND preserves and adds. File must be closed before reopening in different mode.
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Q: Explain UPGRADE attribute
Answer:
UPGRADE keeps AIX synchronized with base cluster. Changes to base automatically update upgraded AIX. Adds overhead to writes. Non-upgrade AIX needs manual BLDINDEX. Use UPGRADE for real-time currency.
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Q: How to define group level items?
Answer:
Group items contain subordinate items. 01 WS-DATE. 05 WS-YEAR PIC 9(4). 05 WS-MONTH PIC 99. 05 WS-DAY PIC 99. Group is alphanumeric regardless of contents. MOVE WS-DATE moves all 8 bytes. Reference individual or group.
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Q: What is DEFINE PATH?
Answer:
PATH associates AIX for access. DEFINE PATH(NAME(path.name) PATHENTRY(aix.name)). Required to access via AIX. Open PATH in program, not AIX directly. UPDATE option allows updates via path.
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Q: How to access AIX?
Answer:
Open PATH to AIX, not base cluster. READ via alternate key. Can browse by alternate key sequence. Updates depend on PATH UPDATE option. Non-unique AIX returns first, then READ NEXT for others.
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Q: Explain IDENTIFICATION DIVISION
Answer:
IDENTIFICATION DIVISION identifies program. PROGRAM-ID required (up to 8 chars for compatibility). AUTHOR, DATE-WRITTEN, DATE-COMPILED, REMARKS are documentation. INSTALLATION for deployment info. Only PROGRAM-ID affects compilation.
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Q: What is TYPRUN parameter?
Answer:
TYPRUN options: SCAN (syntax check, no execution), HOLD (submit but hold), COPY (copy JCL to SYSOUT), JCLHOLD (hold with JCL). TYPRUN=SCAN validates JCL without running. Useful for testing complex JCL before production.
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Q: Explain REWRITE command
Answer:
REWRITE updates record. Must READ with UPDATE first. EXEC CICS REWRITE FILE(name) FROM(data) LENGTH(len). Changes record held from READ. Cannot change key. TOKEN matches UPDATE-READ.
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Q: What is DELETE command?
Answer:
DELETE removes record. EXEC CICS DELETE FILE(name) RIDFLD(key). Or after READ UPDATE: DELETE FILE(name). KEYLENGTH/GENERIC for range delete. NOTFND if key missing. NUMREC returns count deleted.
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Q: What is RETPD parameter?
Answer:
RETPD=nnn specifies retention days. Cannot delete until expired. EXPDT=yyddd for specific date. EXPDT=99365 or RETPD=9999 for permanent. Security software may override. Affects tape and disk datasets.
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Q: How to use JCLTEST?
Answer:
TYPRUN=JCLTEST validates JCL without execution. Checks syntax, dataset names, authorization. Some systems support TYPRUN=SCAN which is similar. Submit job and check messages. No resources actually allocated.
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Q: Explain EXPDT parameter?
Answer:
EXPDT=yyddd or EXPDT=yyyyddd expiration date. After this date, dataset can be deleted. EXPDT=99365 effectively permanent (1999 or 2099). RETPD alternative. Security software may enforce or override.
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Q: What causes NOT DEFINED TO CATALOG?
Answer:
Dataset exists on volume but not cataloged. Solutions: DISP=OLD,VOL=SER=volume, or catalog with IDCAMS DEFINE NONVSAM. Check correct catalog alias. May need ICF catalog update.
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Q: Explain DECLARE CURSOR syntax
Answer:
DECLARE cursor-name CURSOR FOR SELECT... WITH HOLD keeps open after COMMIT. WITH RETURN returns to caller. FOR UPDATE OF allows positioned update. FOR READ ONLY optimizes read. ORDER BY for sorting. Static or dynamic declaration.
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Q: What is BIND command?
Answer:
BIND creates plan/package from DBRM. BIND PLAN(name) MEMBER(dbrm). Options: ISOLATION, VALIDATE, EXPLAIN. REBIND updates existing. BIND PACKAGE for packages. Precompile creates DBRM, BIND makes executable.
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Q: What is MERGE statement?
Answer:
MERGE updates or inserts conditionally. MERGE INTO target USING source ON condition WHEN MATCHED THEN UPDATE WHEN NOT MATCHED THEN INSERT. Combines INSERT/UPDATE logic. Efficient for sync operations.
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Q: Explain NOFOR option in SELECT?
Answer:
NOFOR prevents FOR UPDATE locking. SELECT ... NOFOR. Read-only access without lock overhead. For display-only queries. Cannot UPDATE WHERE CURRENT OF cursor with NOFOR.