Improve unparsing after optimize_projections optimization #13599
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sgrebnov
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Nov 29, 2024
| @@ -926,12 +926,25 @@ fn test_table_scan_pushdown() -> Result<()> { | |||
| let query_from_table_scan_with_projection = LogicalPlanBuilder::from( | |||
| table_scan(Some("t1"), &schema, Some(vec![0, 1]))?.build()?, | |||
| ) | |||
| .project(vec![wildcard()])? | |||
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Can this actually be a real plan (other than manually constructed) with a wildcard projection and a TableScan that includes only two columns?
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Which issue does this PR close?
Follow-up item for Support unparsing plans after applying the
optimize_projectionsrule PR, focusing on the unparsing enhancement to support the described scenario.With the
optimize_projectionsoptimization, columns are pushed down to theTableScan, resulting in bothProjectionandTableScannodes containing projection information. As a result, the generated SQL contains a duplicate subquery, e.g.,SELECT a, b FROM (SELECT a, b FROM my_table).What changes are included in this PR?
PR updates
unparse_table_scan_pushdownto prevent the creation of an additional projection if the unparser already includes a projection (SELECT) part.Are these changes tested?
Yes, TPC-H, TPC-DS benchmark tests, unit tests.
Are there any user-facing changes?
Improved Plan-to-SQL conversion when a TableScan with projection information is wrapped in a Projection.