Easytrieve SELECT Control Flow

Pipeline Control Flow Model

Batch programs chain stages: input, optional prescreen, transform, sort, report. SELECT operates at stage boundaries as yes-no continue switch for current record. IF evaluates business rules; SELECT commits record to next stage when rules pass. Think of SELECT as opening a turnstile—IF checks ticket, SELECT rotates gate. Without SELECT turnstile stays closed regardless of IF calculations elsewhere.

Sort Prescreen Control Flow

SORT INPUT WITH BEFORE-SCREEN-PROC pattern: every input record enters BEFORE procedure; valid records hit SELECT; invalid records EXIT or fall through without SELECT. Downstream SORT sees subset. Control flow splits early—downstream JOB INPUT on sort work file processes only selected population. Empty output file often means zero SELECT executions—trace BEFORE with counts before blaming sort keys.

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SORT INPUT USING (DEPT, EMP-NO)
  BEFORE SCREEN-PROC
 
SCREEN-PROC. PROC
  IF DEPT EQ 'SALES' AND STATUS EQ 'A'
     SELECT
  END-IF
END-PROC

IF Then SELECT Pattern

Common structure: IF complex condition, SELECT, END-IF. IF alone never includes record in sort output. Nested IF may SELECT on one branch only—control flow tree ends in SELECT leaf for inclusion paths. ELSE branch intentionally omits SELECT to exclude. Multiple IF paths may SELECT same record—still one output row per input pass.

SELECT and STOP Interaction

SELECT sets inclusion; STOP in same procedure pass may cancel processing before sort commits row. Broadcom documents SELECT followed by STOP as not selected—order matters inside procedure. Error handlers: IF FATAL, STOP without SELECT drops bad record from extract while ending procedure pass cleanly. Test STOP paths in BEFORE proc so production rejects do not accidentally SELECT then STOP inconsistently across releases.

REPORT-INPUT Gating Flow

PRINT selects detail lines for printing; REPORT-INPUT SELECT further gates which selected data continues into report writer internal processing—totals, breaks, spooling paths. Omit REPORT-INPUT and defaults apply per product rules. When REPORT-INPUT exists, unselected records bypass continued report processing even if PRINT fired—control-flow mismatch shows as missing totals for printed lines. Align PRINT, REPORT-INPUT, and business IF logic in one specification table.

SELECT Versus Field-Level CASE

CASE routes execution within record processing—assign rates, messages, PERFORM paths. SELECT routes record to next pipeline stage. Same record may CASE on type for calculations then SELECT for sort inclusion if type in allowed set. Layer decisions: field logic first, pipeline gate last in BEFORE proc.

SQL SELECT Control Flow Contrast

JOB INPUT SQL with full SELECT clause defines cursor-like input stream from database—control enters JOB with rows from query, not sequential file READ. One SELECT per JOB activity rule applies. Flow diagram source is DBMS not disk file. Do not mix sort one-word SELECT grammar into SQL clause or vice versa—compile errors or wrong semantics.

Debugging Empty Pipeline Stages

1. Count input records to BEFORE procedure entry.
2. Count SELECT executions via W counter in BEFORE proc.
3. Compare sort output record count to SELECT count.
4. Verify STOP not canceling SELECT unintentionally.
5. Confirm SORT names correct BEFORE procedure label.

Common SELECT Control Mistakes

• IF validation without SELECT in sort BEFORE.
• Assuming SQL SELECT includes records in sort extract.
• REPORT-INPUT never SELECT—report totals missing.
• Duplicate BEFORE procs—wrong label on SORT statement.
• SELECT outside BEFORE or REPORT-INPUT context where invalid.

Explain It Like I'm Five

SELECT is putting a green sticker on a paper that says this one may go to the next room. IF checks if the paper is good; SELECT is the sticker that lets it through the door. No sticker means the paper stays out even if you wrote notes on it. Sort and report rooms only accept papers with stickers.

Exercises

1. Draw pipeline: file → BEFORE → SELECT → sort → report.
2. Write BEFORE proc IF status SELECT pattern.
3. Explain empty sort file when IF ran 1000 times.
4. Contrast one-word SELECT with SQL SELECT clause.
5. Add counter DISPLAY for SELECT count in test job.