# 03-matching-N-1: N:1 Matching (N master records match one detail record)

## 电信业务场景

多线路→请求书汇集。读取多条电话线路记录(LINE)和请求地址文件(BILL-ADDR)，按地址进行N:1汇集。同一个地址的多条线路汇总到一张请求书。

## Description

Tests N:1 matching where multiple master records sharing the same key match
a single detail record. The program groups masters by key, finds the
corresponding detail, and writes one output record per master that has a match.

## Record Layout

| Field      | Type            | Length | Description               |
|------------|-----------------|--------|---------------------------|
| STD-KEY    | PIC X           | 10     | Record key                |
| STD-DATA-1 | PIC X           | 20     | Description text          |
| STD-DATA-2 | PIC 9           | 10     | Numeric data (display)    |
| STD-DATA-3 | PIC S9(7)V99    | 05     | Numeric data (COMP-3)     |

Total record length: 45 bytes.

## Files

| File                        | Purpose                           |
|-----------------------------|-----------------------------------|
| main-03-matching-N-1.cbl    | Main COBOL program (fixed format) |
| data-gen.sh                 | Generate test data files          |
| run.sh                      | Compile, run, verify              |
| README.md                   | This file                         |

## Data

- **master.dat**: 3 records, all with key `KEY00001` (N=3 masters)
- **detail.dat**: 2 records — `KEY00001` (matches the 3 masters),
  `KEY00002` (unmatched, not referenced)

## Matching Logic

1. Read masters by group (all records sharing the same key).
2. Advance the detail pointer to find a key matching the group.
3. If a match is found, write one output record per master in the group.
4. If no match is found, skip the entire master group.
5. Unmatched detail records are also skipped.

## Test

| Check                  | Expected               |
|------------------------|------------------------|
| Output records         | 3 (3 masters x 1 match) |
| Output file size       | 135 bytes (3 x 45)     |
| Unmatched master groups| 0 (all 3 have a match) |

## Usage

```bash
cd 03-matching-N-1
bash run.sh
```