1fanwang opened a new pull request, #71258:
URL: https://github.com/apache/airflow/pull/71258
The MySQL branch of this downgrade passes two statements to a single
`op.execute()`:
```python
op.execute(
"""
SET @row_number = 0;
UPDATE task_instance_history
SET id = (@row_number := @row_number + 1)
ORDER BY try_id;
"""
)
```
PyMySQL does not enable `CLIENT.MULTI_STATEMENTS`, so it rejects the script
with a syntax error and the downgrade cannot run. mysqlclient does enable it,
which is why the problem is invisible to anyone on that driver, including CI:
`scripts/ci/docker-compose/backend-mysql.yml` uses a bare `mysql://` URL, which
SQLAlchemy resolves to `mysqldb`.
Splitting into two `op.execute()` calls fixes it. `op.execute()` reuses
`op.get_bind()`, so `@row_number` is still visible to the `UPDATE`.
Same class of bug as PR https://github.com/apache/airflow/pull/70235, which
fixes the multi-statement SQL in `0017_2_9_2`. I found this one while looking
at that PR. The two do not overlap.
### Testing Done
MySQL 8.4, the migration's own SQL against both drivers, before and after.
<details><summary>Raw logs</summary>
Table seeded with `try_id` out of order (`30, 10, 20`) so the renumbering is
observable:
```
CURRENT OK mysqlclient -> [(10, 1), (20, 2), (30, 3)]
CURRENT FAIL PyMySQL ProgrammingError:
(pymysql.err.ProgrammingError) (1064,
"You have an error in your SQL syntax; check
the manual t...")
FIXED OK mysqlclient -> [(10, 1), (20, 2), (30, 3)]
FIXED OK PyMySQL -> [(10, 1), (20, 2), (30, 3)]
```
The fix produces identical numbering on both drivers, confirming the session
variable survives across the two calls and the `ORDER BY try_id` sequencing is
unchanged.
</details>
Static checks pass, including `Update migration ref doc` and
`mypy-airflow-core`.
---
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