Improve unparsing after optimize_projections optimization #13599
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
sgrebnov
commented
Nov 29, 2024
sgrebnov
force-pushed
the
sgrebnov/improve-unparsing-optimize-projections
branch
from
c5cbff5 to
5ef7fb3
Compare
|
@phillipleblanc do you potentially have time to review this PR? |
phillipleblanc
approved these changes
Dec 3, 2024
There was a problem hiding this comment.
These changes make sense to me.
It basically leverages the fact that since we know we already have a projection, the column projection information in the table scan is redundant - it would be an error for the table scan column projection to have fewer columns than the outer projection expects, and having more columns doesn't matter, since they get filtered by the outer projection anyway.
|
Thanks @sgrebnov and @alamb @phillipleblanc for reviewing |
5 tasks
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
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.