adwaitm1301 opened a new pull request, #42639:
URL: https://github.com/apache/superset/pull/42639
### SUMMARY
Fixes #42386
When a string column on a physical dataset is manually marked as temporal,
Superset passes it straight into `DATE_TRUNC`, which PostgreSQL rejects because
`DATE_TRUNC` has no overload for `character varying`:
```
SELECT DATE_TRUNC('day', event_timestamp) AS event_timestamp, ...
```
This change makes `PostgresBaseEngineSpec.get_timestamp_expr` cast the
column to `TIMESTAMP` before applying the grain when the underlying SQLAlchemy
type is a string type. It builds on the existing override that handles pure
`DATE` columns (see #42254), so both cases stay in one place.
Behavior that is intentionally left unchanged:
- `DATE` columns are still cast back to `DATE` after truncation, preserving
the fix from #42254.
- `TIMESTAMP`/`DATETIME` columns are not cast.
- Epoch-based formats (`epoch_s`, `epoch_ms`) and bare years (`%Y`) keep
their existing expressions.
- Columns without a grain, or without a known type, are not touched.
### BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF
Not applicable.
### TESTING INSTRUCTIONS
1. Create a PostgreSQL table with a `VARCHAR` column holding timestamps,
following the repro steps in #42386.
2. Create a physical dataset and mark the column as temporal.
3. Build a time series chart with a day grain and run it. The query now
renders as:
```sql
SELECT DATE_TRUNC('day', CAST(event_timestamp AS TIMESTAMP)) AS
event_timestamp, ...
```
4. Run the new unit tests:
```
pytest tests/unit_tests/db_engine_specs/test_postgres.py -k
get_timestamp_expr
```
### ADDITIONAL INFORMATION
- [x] Has associated issue: #42386
- [ ] Required feature flags:
- [ ] Changes UI
- [ ] Includes DB Migration (follow approval process in
[SIP-59](https://github.com/apache/superset/issues/13351))
- [ ] Migration is atomic, supports rollback & is backwards-compatible
- [ ] Confirm DB migration upgrade and downgrade tested
- [ ] Runtime estimates and downtime expectations provided
- [ ] Introduces new feature or API
- [ ] Removes existing feature or API
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