Method
Effective unit price = discounted_price ÷ min_qty (min_qty defaults to 1 when missing or non-positive; for weighted-produce promos min_qty is in kilograms). Discount % = (1 − effective ÷ regular) × 100. Items joined on ItemCode, deduplicated per chain. Filtered: regular ≥ ₪2, discount 1–95%.