Disallow Nested LOOP AT Statements Without FROM or GROUP BY

WarningPerformance & Database#EC NO_NESTED_LOOPRemote Enabled

Overview

Disallow nested LOOP AT statements.

ATC Finding Message: Nested LOOP AT detected; avoid O(N*M) loops or use GROUP BY or parallel cursor

Rationale

Nesting internal table loops (LOOP AT within LOOP AT) creates O(N*M) Cartesian complexity that scales poorly with larger datasets and degrades application performance. Use GROUP BY loops, hashed/sorted secondary keys, or parallel cursor (LOOP AT itab FROM sy-tabix) instead.

Non-Compliant

LOOP AT lt_orders INTO ls_order.
  LOOP AT lt_items INTO ls_item.
    " O(N*M) quadratic loop
  ENDLOOP.
ENDLOOP.

Compliant

LOOP AT lt_orders INTO ls_order.
  LOOP AT lt_items INTO ls_item FROM lv_start WHERE order_id = ls_order-order_id.
    " Parallel cursor or filtered loop
  ENDLOOP.
ENDLOOP.

Suppression

To suppress findings for this rule, append the pseudo-comment to the statement:

" Standard pseudo-comment:
... "#EC NO_NESTED_LOOP

" SAP CI_ prefix format:
... "#EC CI_NO_NESTED_LOOP

Related Rules

• Prefer LOOP AT WHERE over IF CONTINUE Guards — #EC PREF_LOOP_WHERE
• Modernize READ TABLE (Table Expressions & line_exists) — #EC PREF_TAB_EXPR
• Limit Jump Statements (CONTINUE, EXIT) per Loop — #EC MAX_LOOP_JUMPS

Technical Details

• Native ATC Class: ZCL_SKYLINT_NO_NESTED_LOOP
• Implementation File: zcl_skylint_no_nested_loop.clas.abap