# 32-mix-1N-samekeybreak — 1:N Matching with Same-Key Break

## 电信业务场景

合同+月别混合集计。先做合同↔CDR的1:N匹配，再在匹配结果内做同键(key)的月别集计。同时演示匹配和key切两种模式。

## Purpose
Demonstrates 1:N matching pattern (one master to many details) combined with same-key break summarization.

## Test Coverage
1. **1:N matching** — One master (KEY0000001) matched to three detail records
2. **Same-key break** — When detail key changes, a summary line is output with count and total
3. **Multiple master matches** — Records for KEY0000001, KEY0000002, KEY0000004
4. **Unmatched detail** — Master lookup not found (if key is missing)
5. **Final break** — Last group summary at end of file

## Data
- 5 master records (KEY0000001 through KEY0000005)
- 8 detail records with keys repeating for 1:N matching

## Key Techniques
- In-memory master table loaded from file
- Sequential file matching
- Key break detection on key field change
- Accumulator reset at each break
- Grand total across all matches