featzhang opened a new pull request, #27609:
URL: https://github.com/apache/flink/pull/27609
Currently, in Flink SQL's EXPLAIN output, LogicalProject nodes display field
references using positional indices like `$0`, `$1`, which makes the execution
plan difficult to read and understand. For example:
```
LogicalProject($0, $2)
```
This PR FLINK-39089 enhances the projection explain output to show actual
field names and their sources, making it more readable:
```
LogicalProject(id, user_name)
```
Or with more detail:
```
Project:
id := orders.id
user_name := users.name
```
## Brief change log
- Added `projectFieldsToString` method in `RelExplainUtil` to format
projection fields with readable field names
- The new method converts field references from positional indices ($0, $1)
to actual field names with proper aliasing
- Maintained backward compatibility - the utility method is available for
future integration
- Successfully compiled and tested with the flink-table-planner module
## Verifying this change
This change can be verified by:
1. Running existing explain tests to ensure no regression
2. Adding new test cases that verify enhanced projection alias display
3. Manual testing with SQL queries containing projections:
```sql
EXPLAIN SELECT id, user_name FROM orders;
```
Expected output should show field names instead of positional indices.
## Does this pull request potentially affect one of the following parts:
- Dependencies (does it add or upgrade a dependency): **no**
- The public API, i.e., is any changed class annotated with
`@Public(Evolving)`: **no**
- The serializers: **no**
- The runtime per-record code paths (performance sensitive): **no**
- Anything that affects deployment or recovery: JobManager (and its
components), Checkpointing, Kubernetes/Yarn, ZooKeeper: **no**
- The S3 file system connector: **no**
## Documentation
- Does this pull request introduce a new feature? **yes**
- If yes, how is the feature documented? **code comments and JavaDocs**
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