ShashidharM0118 opened a new pull request, #19419:
URL: https://github.com/apache/datafusion/pull/19419
## Which issue does this PR close?
- Closes #19416
## Rationale for this change
Currently, when projecting literal values (constants) in projection
operations, the statistics are set to unknown
(`ColumnStatistics::new_unknown()`). This prevents the optimizer from using
constant column information for various optimizations, such as:
- Sort elimination when sorting by constant columns
## What changes are included in this PR?
1. **Updated `project_statistics` method** in `ProjectionExprs`:
- Added detection and statistics calculation for `Literal` expressions
(non-null constants)
- Statistics calculated: `min_value = max_value = literal value`,
`distinct_count = 1`, `null_count = 0`, `byte_size = data_type_width ×
num_rows` (for primitive types)
- NULL literals return `ColumnStatistics::new_unknown()`
2. **Added test**:
- `test_project_statistics_with_literal`: Tests non-null literal
statistics
## Are these changes tested?
Yes
## Are there any user-facing changes?
No
## Example
**Before this change:**
`SELECT 42 AS status, name FROM users ORDER BY status ` - Statistics for
`status` were unknown
- Optimizer couldn't eliminate the sort operation
**After this change:**
`SELECT 42 AS status, name FROM users ORDER BY status` - Statistics show
`status` has `min_value = max_value = 42`, `distinct_count = 1`
- Optimizer can eliminate the sort since the column is already sorted (all
values are the same)
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