Internal Tables Part 3: Work Area vs Field Symbol vs Data Reference

📌 KEY POINTS
✅ INTO wa copies the row; changes need MODIFY to go back into the table.
✅ ASSIGNING <fs> points directly at the row; changes are immediate — no MODIFY, no copy.
✅ REFERENCE INTO lr stores a pointer you can keep (e.g. in another table).
⚠️ Check IS ASSIGNED / IS BOUND before use; never change key fields of sorted/hashed tables via <fs>.

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▶ WHERE WE ARE
Parts 1–2 read rows into work areas. For changing data and for large tables, the access technique matters.

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▶ 1. WORK AREA (COPY)
LOOP AT gt_flights INTO gs_flight.
gs_flight-price = gs_flight-price * '1.1'.
MODIFY gt_flights FROM gs_flight. " write back (index of current loop row)

ENDLOOP.

• Safe and simple; the table changes only with MODIFY.
• Costs a copy per row — noticeable for wide rows or big tables.

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▶ 2. FIELD SYMBOL (POINTER-LIKE)
FIELD-SYMBOLS <ls_flight> TYPE ty_flight.
LOOP AT gt_flights ASSIGNING <ls_flight>.
<ls_flight>-price = <ls_flight>-price * '1.1'. " changes the table row directly

ENDLOOP.

• No copy, no MODIFY — fastest for changes.
• After a failed READ … ASSIGNING, the field symbol is not assigned → check IS ASSIGNED.
• Don't modify key fields of sorted or hashed tables (runtime error).

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▶ 3. DATA REFERENCE
DATA lr_flight TYPE REF TO ty_flight.
LOOP AT gt_flights REFERENCE INTO lr_flight.
lr_flight->price = lr_flight->price * '1.1'.

ENDLOOP.

• Like a field symbol, but a variable: can be stored, passed and put into tables of references.
• Check IS BOUND before dereferencing.

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▶ 4. WHICH ONE WHEN

• Read-only, small rows → work area (clear and simple).
• Changing rows in a loop → field symbol.
• Need to remember rows for later (e.g. link objects) → data reference.
• Very wide rows (hundreds of fields) and large tables → field symbol even for reading.

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▶ 5. READ TABLE VARIANTS
READ TABLE gt_flights INTO gs_flight WITH KEY … (copy)
READ TABLE gt_flights ASSIGNING <ls_flight> WITH KEY … (point)
READ TABLE gt_flights TRANSPORTING NO FIELDS WITH KEY … (existence check only, sy-subrc/sy-tabix)

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▶ STEP BY STEP

1. Run the three loops in the code example on SFLIGHT data.
2. Compare runtimes with GET RUN TIME.
3. Try a READ … ASSIGNING that fails and see the IS ASSIGNED check.

💡 Modern syntax (7.40+): LOOP AT … ASSIGNING FIELD-SYMBOL(<fs>), REFERENCE INTO DATA(lr).

✅ CHECKPOINT: you choose the access technique consciously and change tables without unnecessary copies.

A pricing update program looped over 1.5 million condition records INTO a work area and used MODIFY for every row. The job ran for 40 minutes and used a lot of memory copying 120-field rows.
Switching to LOOP … ASSIGNING with direct field changes removed both the copies and the MODIFY statements. Runtime dropped to under 10 minutes with identical results. A code review rule was added: "changing loops use field symbols".

• Changing a work area and forgetting MODIFY.
• Using a field symbol after a failed READ without IS ASSIGNED.
• Changing key fields of sorted/hashed tables through field symbols.
• Dereferencing an unbound data reference.
• Copying wide rows into work areas in large loops.

• Use field symbols for changing loops and large tables.
• Use work areas for simple, read-only processing.
• Use data references when rows must be stored or passed.
• Check IS ASSIGNED / IS BOUND.
• Use TRANSPORTING NO FIELDS for pure existence checks.

Questions: "Difference between work area and field symbol?", "Why use ASSIGNING in loops?", "When use REFERENCE INTO?"
Strong answer: INTO copies the row (needs MODIFY to change the table), ASSIGNING points to the row (changes are direct, no copy — faster), REFERENCE INTO provides a storable pointer; check IS ASSIGNED/IS BOUND; do not change keys of sorted/hashed tables; use TRANSPORTING NO FIELDS for existence checks.