# 16-matching-2stage-1-1: Two-Stage 1:1 Matching

## 电信业务场景

二级请求书核对。两段式1:1对账处理。第一段:请求书与支付对账→中间文件；第二段:中间文件与调整记录对账→最终结果。

## Description

Tests a two-stage pipeline where the output of the first 1:1 match feeds
into a second 1:1 match. Three-way chained matching across FILE-A, FILE-B,
and FILE-C using an intermediate TEMP-FILE.

- Stage 1: Match FILE-A and FILE-B (1:1), write matched A-side records to
  TEMP-FILE. Unmatched records (KEY00004 in A, KEY00005 in B) are skipped.
- Stage 2: Match TEMP-FILE and FILE-C (1:1), write matched records to
  FINAL-OUT. Unmatched C records (KEY00006) are skipped.

## 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-16-matching-2stage-1-1.cbl| Main COBOL program (two stages)     |
| data-gen.sh                   | Generate three test data files       |
| run.sh                        | Compile, run, verify                 |
| README.md                     | This file                            |

## Data

| File        | Records                                                |
|-------------|--------------------------------------------------------|
| file-a.dat  | KEY00001, KEY00002, KEY00003, KEY00004 (unmatched)     |
| file-b.dat  | KEY00001, KEY00002, KEY00003, KEY00005 (unmatched)     |
| file-c.dat  | KEY00001, KEY00002, KEY00003, KEY00006 (unmatched)     |

The matching chain: KEY00001, KEY00002, KEY00003 exist in all three files
and should survive both stages. The unmatched extras are discarded.

## Matching Logic

Each stage implements standard 1:1 sorted merge/match:
1. Compare keys from both input streams.
2. If keys are equal, write a matched record and advance both.
3. If keys differ, advance the stream with the smaller key (skip it).
4. Continue until one stream is exhausted.

## Test

| Check                    | Expected                          |
|--------------------------|-----------------------------------|
| Stage 1 output (temp)    | 3 records x 45 = 135 bytes        |
| Stage 2 output (final)   | 3 records x 45 = 135 bytes        |
| Matched chain            | KEY00001, KEY00002, KEY00003      |
| Unmatched filtered       | KEY00004, KEY00005, KEY00006      |

## Usage

```bash
cd 16-matching-2stage-1-1
bash run.sh
```