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Q: What is identity column?
Answer:
Identity column auto-generates values. col INTEGER GENERATED ALWAYS AS IDENTITY. Or GENERATED BY DEFAULT (allows override). Start, increment configurable. Alternative to sequence for single-table keys.
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Q: How to delete VSAM cluster?
Answer:
IDCAMS DELETE ds.name CLUSTER. Or DELETE ds.name FILE(ddname) if DD provided. PURGE overrides retention. ERASE clears data. DELETE removes catalog entry and data/index components.
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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 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 code symbolic override?
Answer:
EXEC proc,SYM1=value1,SYM2=value2. Symbols defined in PROC with SET or & default. Override replaces default. Multiple overrides comma-separated. Must match PROC symbols. Case sensitive.
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Q: What is DATACLAS parameter?
Answer:
DATACLAS assigns SMS data class. DATACLAS=classname. Defines DCB attributes, space, data type. ACS routines may assign automatically. Overrides explicit DCB. Simplifies JCL. Installation-defined classes.
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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 DEFINE MODEL?
Answer:
MODEL copies attributes from existing cluster. DEFINE CLUSTER(NAME(new) MODEL(existing)). Only copies definition, not data. Useful for creating similar clusters. Can override specific parameters.
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Q: What is STEPLIB vs JOBLIB?
Answer:
JOBLIB at job level provides program libraries for all steps. STEPLIB at step level overrides JOBLIB for that step. STEPLIB takes precedence. Both searched before LINKLIST. Multiple libraries concatenated. DDN must be STEPLIB/JOBLIB exactly.
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Q: Explain referback DD
Answer:
Referback references earlier DD: DSN=*.STEP1.DDNAME or DSN=*.DDNAME (same step). Copies DSN and DISP. Can override other parameters. VOL=REF=*.STEP1.DD copies volume. Useful for chained processing.
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Q: What is UNIT parameter?
Answer:
UNIT specifies device type. UNIT=SYSDA (direct access), UNIT=TAPE, UNIT=3390. UNIT=AFF=ddname shares device. UNIT=(SYSDA,2) allocates 2 volumes. SMS may override. UNIT=VIO for virtual I/O (memory only).
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Q: What is VOL parameter?
Answer:
VOL specifies volume. VOL=SER=PACK01 specific volume. VOL=REF=*.STEP.DD copies volume from previous. VOL=(,RETAIN) keeps volume mounted. VOL=(,,,5) allows 5 volumes. SER overrides SMS placement. Use cautiously.
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Q: Explain LIKE parameter
Answer:
LIKE copies DCB attributes from existing dataset. DCB=*.STEP1.DD or LIKE=catalog.dataset. Simplifies JCL. Model dataset must exist or be allocated earlier. Override specific attributes: DCB=(LIKE=...,LRECL=100).
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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: What is AMP parameter?
Answer:
AMP specifies VSAM buffer parameters. AMP='BUFNI=8,BUFND=4' for index/data buffers. AMP='AMORG' for VSAM organization. OPTCD for options. Overrides VSAM cluster definitions for this run. Affects performance.
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Q: How to override PROC DD?
Answer:
//procstep.ddname DD overrides. //MYSTEP.SYSOUT DD SYSOUT=H changes SYSOUT class. Can add parameters or replace entirely. Add new DD: //MYSTEP.NEWDD DD DSN=... Position after EXEC procname.
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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.