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Q: What is CTE (Common Table Expression)?
Answer:
CTE defines temporary result set. WITH cte_name AS (SELECT...) SELECT * FROM cte_name. Improves readability. Can be recursive for hierarchies. Multiple CTEs comma-separated. Referenced in main query. Scope is single statement.
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Q: What is the difference between SECTION and PARAGRAPH in COBOL?
Answer:
SECTION:
- Contains one or more paragraphs
- Ends with next SECTION or end of program
- Used for logical grouping
- Can be performed as a unit
PARAGRAPH:
- Basic unit of code
- Named block of statements
- Ends at next paragraph name or SECTION
PERFORM SECTION-NAME executes all paragraphs in the section.
PERFORM PARA-NAME executes only that paragraph.
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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 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 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: How to use CONTINUE statement?
Answer:
CONTINUE is a no-operation placeholder. Useful in EVALUATE when certain conditions need no action: WHEN 'X' CONTINUE. In IF: IF condition CONTINUE ELSE action. Maintains structure without dummy statements. Not a GOTO target.
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Q: Explain START statement for VSAM
Answer:
START positions for sequential READ. START filename KEY IS EQUAL/GREATER/NOT LESS THAN key-field. After successful START, READ NEXT retrieves records sequentially from that position. INVALID KEY handles not-found condition.
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Q: How to use EXPLAIN tables?
Answer:
PLAN_TABLE primary output. DSN_STATEMNT_TABLE for cost. DSN_FUNCTION_TABLE for functions. INSERT EXPLAIN before statement. Query tables after. PLANNO, ACCESSTYPE, MATCHCOLS important columns.
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Q: Explain EXEC SQL statements
Answer:
EXEC SQL marks embedded DB2 SQL. EXEC SQL SELECT col INTO :host-var FROM table WHERE key = :key-var END-EXEC. Colon prefix for host variables. SQLCODE in SQLCA indicates result. Precompiler converts to COBOL calls.
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Q: How to use STRING with POINTER?
Answer:
STRING uses POINTER to track position: STRING field-1 DELIMITED SIZE INTO output WITH POINTER pos-var. Pointer shows next available position. Initialize before first STRING. Check for overflow. Continue STRING in multiple statements.
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Q: What is ALTER statement?
Answer:
ALTER changes GO TO target dynamically. ALTER para-1 TO PROCEED TO para-2. Obsolete-causes maintenance nightmares. Makes flow unpredictable. Use EVALUATE or SET/IF instead. Some shops prohibit. Still legal but strongly discouraged.
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Q: How to use PERFORM EXIT?
Answer:
EXIT statement marks paragraph end. PERFORM PROCESS-DATA THRU PROCESS-EXIT. Process-exit paragraph contains only EXIT. Ensures consistent exit point. Can also GO TO exit paragraph. EXIT PROGRAM in subprogram returns to caller.
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Q: How to handle VSAM in batch?
Answer:
Define cluster with IDCAMS. JCL DD statement references cluster. COBOL SELECT maps to DD. ACCESS MODE matches operations. Close properly. STATUS check after operations.
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Q: What is symbolic parameter?
Answer:
Symbols are variables: SET symbol=value or &symbol on JOB/PROC. Reference: DSN=&HLQ..DATA. Resolved at job entry. EXEC proc,symbol=value overrides. SET statement defines. Symbols start with & and up to 8 characters.
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Q: How does OUTPUT statement work?
Answer:
OUTPUT defines SYSOUT processing options. //OUT1 OUTPUT CLASS=A,DEST=LOCAL,COPIES=2. Reference: //SYSOUT DD SYSOUT=*,OUTPUT=*.OUT1. Centralizes output attributes. Can specify JESDS for JES-level control. Forms, burst options available.
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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: What causes S0C7 in batch?
Answer:
S0C7 is data exception - non-numeric in numeric field. Check: input file data quality, initialize variables, correct REDEFINES, field alignment. Use OFFSET in dump to find statement. LE CEEDUMP shows data values. Common with new programs.
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Q: How to concatenate datasets?
Answer:
Stack DD statements: //INPUT DD DSN=FILE1,DISP=SHR // DD DSN=FILE2,DISP=SHR. No DD name on continuation. Read consecutively as one file. Different LRECL needs LRECL on first DD or DCB parameter. Concatenation limit varies by system.
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Q: What is IEBGENER utility?
Answer:
IEBGENER copies sequential datasets. SYSUT1=input, SYSUT2=output, SYSIN=control. Simple copy needs only SYSUT1/SYSUT2/SYSIN DD DUMMY. Can reformat, generate, edit records with SYSIN statements. Being replaced by ICEGENER.
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Q: What is DD DATA statement?
Answer:
DD DATA marks instream data with delimiter. DD DATA,DLM=XX...data...XX. Default delimiter is /*. DLM needed when data contains /*. Data physically follows DD in JCL stream. Alternative: DD * for default delimiter.
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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 use //IF statement?
Answer:
//IF (condition) THEN executes following steps if true. Conditions: RC, ABEND, ABENDCC, RUN, STEP.RC. Example: //IF (STEP1.RC = 0) THEN ... //ENDIF. Can nest. ELSE available. Clearer than COND parameter.
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Q: What is JESDS parameter?
Answer:
JESDS specifies JES dataset for OUTPUT. JESDS=ALL creates JESMSGLG, JESJCL, JESYSMSG. JESDS=LOG for JESMSGLG only. On OUTPUT statement. Controls system output generation. Used for output management.
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Q: What is SYSIN DD *?
Answer:
SYSIN DD * starts instream data. Data follows until /*. Program reads via SYSIN DD. Common for utility control statements. DD DATA,DLM=xx if data contains /*. SYSIN DD DUMMY for no input.
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Q: Explain DD PATH statement?
Answer:
PATH specifies Unix/USS file. PATH='/u/user/file'. Used instead of DSN. PATHDISP for disposition. PATHOPTS for options. PATHMODE for permissions. Integrates USS files into batch JCL.
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Q: What is FILEDATA parameter?
Answer:
FILEDATA specifies DCB for NFS/USS. FILEDATA=TEXT or BINARY. TEXT handles line endings. BINARY transfers unchanged. On PATH DD statements. Affects how data converted between systems.
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Q: What is SEGMENT parameter?
Answer:
SEGMENT limits output lines per dataset. On OUTPUT statement. SEGMENT=nnn pages per segment. JES creates multiple output datasets. Helps with huge print files. Easier to handle smaller pieces.
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Q: Explain DB2 locking
Answer:
DB2 locks at row, page, table, tablespace level. X (Exclusive) for writes, S (Share) for reads. IX/IS for intent. Lock escalation moves to higher level. LOCK TABLE statement forces mode. Timeout if wait too long.
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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: What is stored procedure?
Answer:
Stored procedure is saved SQL code. CREATE PROCEDURE name(params) BEGIN SQL statements END. CALL name(values) executes. Can have IN/OUT/INOUT parameters. Reduces network traffic. Logic in database. Security benefits.
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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 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: What is EVALUATE statement and when to use it?
Answer:
EVALUATE is COBOL's case/switch construct. Syntax: EVALUATE TRUE WHEN condition-1 statement WHEN OTHER default END-EVALUATE. More readable than nested IF for multiple conditions. Can evaluate multiple subjects and use THRU for ranges.
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Q: Explain COMPUTE statement
Answer:
COMPUTE performs arithmetic with expression syntax. COMPUTE RESULT = (A + B) * C / D. Supports + - * / ** operators. ROUNDED option rounds result. ON SIZE ERROR handles overflow. Clearer than separate ADD/SUBTRACT/MULTIPLY/DIVIDE for complex formulas.
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Q: Explain CALL statement and parameters
Answer:
CALL invokes subprogram: CALL 'SUBPROG' USING param-1 param-2. BY REFERENCE (default) passes address. BY CONTENT passes copy. BY VALUE passes value (for C). ON EXCEPTION handles load failures. CANCEL releases memory.
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Q: What is profile table?
Answer:
Profile tables store user-specific optimizer settings. DSN_PROFILE_TABLE, DSN_PROFILE_ATTRIBUTES. Override defaults for specific statements. Use QUERYNO correlation. Advanced tuning technique.
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Q: What is REPLACE statement?
Answer:
REPLACE substitutes text during compilation. REPLACE ==OLD-TEXT== BY ==NEW-TEXT==. Active until REPLACE OFF or next REPLACE. Useful with copybooks for site-specific modifications. Different from COPY REPLACING-more global.
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Q: Explain ENTRY statement
Answer:
ENTRY creates alternate entry point in subprogram. ENTRY 'ALTNAME' USING params. Called program appears under different name. Useful for multiple functions in one load module. Each ENTRY has own parameters. Not standard-use carefully.
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Q: What is TITLE statement?
Answer:
TITLE 'Page Header' sets listing page headers. Appears on each page of compilation listing. Useful for documentation. Multiple TITLES change as encountered. After IDENTIFICATION DIVISION start. Compiler directive, not executable.
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Q: How to handle status 96?
Answer:
Status 96 is no DD statement for file. Check JCL has correct DD name. May be dynamic allocation failure. DD name must match SELECT ASSIGN. Case sensitive in some systems.
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Q: What is file status 47?
Answer:
Status 47 is READ attempted but file not open input. OPEN mode doesn't match operation. Must OPEN INPUT or I-O for READ. Check file OPEN statement and mode.
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Q: Explain DD DUMMY statement
Answer:
DD DUMMY discards output/provides EOF for input. No I/O actually performed. DUMMY, DSN=NULLFILE equivalent. Use to skip optional outputs or provide empty input. Program sees immediate EOF on read. Writes succeed but discarded.
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Q: What is MSGLEVEL parameter?
Answer:
MSGLEVEL=(statements,messages). Statements: 0=JOB only, 1=all JCL, 2=input JCL. Messages: 0=completion only, 1=all including allocation. MSGLEVEL=(1,1) shows everything. MSGLEVEL=(0,0) minimal output. Affects JESMSGLG.
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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 DD SYSOUT statement
Answer:
SYSOUT=class routes output to JES spool. SYSOUT=* uses MSGCLASS from JOB. SYSOUT=A specific class. Additional: COPIES=2, DEST=node.userid, FCB=fcb-name. Held output: HOLD=YES. OUTPUT statement for complex options.
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Q: What is CNTL statement?
Answer:
CNTL groups control statements. //name CNTL establishes scope. //name ENDCNTL ends it. Used with OUTPUT or other complex statements. Provides modularity. Can be referenced by name from multiple DDs.
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Q: What is SPIN parameter?
Answer:
SPIN=UNALLOC releases output immediately on step/job end. SPIN=(UNALLOC,step) at step end. Without SPIN, output held until job completes. Allows viewing long job output early. On DD SYSOUT statement.
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Q: Explain DEST parameter?
Answer:
DEST routes output. DEST=nodeid.userid sends to remote. DEST=LOCAL for local printer. On OUTPUT statement or SYSOUT. JESDS respects DEST. Can be printer name or user. Network delivery support.
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Q: What causes IEF452I error?
Answer:
IEF452I is symbolic substitution error. Symbol not defined or wrong format. Check SET statements, PROC defaults. Verify symbol names match. May be missing &. Case matters for some systems.
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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.
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Q: What is SPUFI?
Answer:
SPUFI (SQL Processing Using File Input) is TSO tool for interactive SQL. Input dataset with SQL statements. Output shows results. Good for testing queries, DDL, quick data checks. Not for production processing.
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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.