CodeWithPravinMaske opened a new issue, #12599:
URL: https://github.com/apache/seatunnel/issues/12599
### Search before asking
- [x] I had searched in the issues and found no similar issues.
### What happened
For a MySQL table **without a primary key** that has a **nullable `UNIQUE
KEY`** column, MySQL-CDC emits `0` instead of `NULL` for that column. Verified
for binlog events on `dev`; the same conversion also applies to snapshot rows
(observed once the snapshot split fix from #12598 lets those rows be read).
This is silent data corruption: the sink receives `0` and no error is reported.
Cause: Debezium 1.9.8, used to parse the table DDL
(`MySqlSchema#parseSnapshotDdl`), promotes the first `UNIQUE KEY` of a table
without a primary key to a primary key and marks its columns NOT NULL
(`CreateTableParserListener#enterUniqueKeyTableConstraint` ->
`MySqlAntlrDdlParser#parsePrimaryIndexColumnNames`, which does
`column.edit().optional(false)` with the comment "MySQL does not allow a
primary key to have nullable columns"). The value conversion then treats the
column as not optional and turns NULL into the type default `0`.
### How to reproduce (MySQL 8.0, verified on `dev`)
```sql
CREATE TABLE shop.no_pk_orders (
id INT NOT NULL,
code INT NULL,
name VARCHAR(32),
UNIQUE KEY uk_code (code)
);
```
Run a MySQL-CDC job on `shop.no_pk_orders` with a Console sink
(`exactly_once = false`), then:
```sql
INSERT INTO shop.no_pk_orders (id, code, name) VALUES (5001, NULL,
'live-null-row'), (5002, 5002, 'live-normal-row');
```
Console output:
```
SeaTunnelRow#kind=INSERT : 5001, 0, live-null-row <-- expected 5001,
null, live-null-row
SeaTunnelRow#kind=INSERT : 5002, 5002, live-normal-row
```
### Expected behavior
NULL values are emitted as NULL. The column nullability should follow the
database (for example `SHOW CREATE TABLE` / JDBC metadata), not the promoted
primary key.
### Related
Found together with #12598, which has the same root cause but a different
symptom (rows skipped by the snapshot).
### SeaTunnel Version
dev (3.0.0-SNAPSHOT)
### Are you willing to submit a PR?
- [x] Yes I am willing to submit a PR!
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