fix: SELECT * EXCLUDE(...) silently returns empty rows when all columns are excluded#21259
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xiedeyantu wants to merge 3 commits intoapache:mainfrom
Open
fix: SELECT * EXCLUDE(...) silently returns empty rows when all columns are excluded#21259xiedeyantu wants to merge 3 commits intoapache:mainfrom
SELECT * EXCLUDE(...) silently returns empty rows when all columns are excluded#21259xiedeyantu wants to merge 3 commits intoapache:mainfrom
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…umns are excluded
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@alamb Sorry to bother you. Could someone please help me review this PR? |
alamb
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Mar 31, 2026
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I think this is an improvement, but I am also confused about EXCEPT vs EXCLUDE in duckdb itself 🤔
Thank you @xiedeyantu
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| # if EXCEPT all the columns, query should still succeed but return empty | ||
| statement ok | ||
| # if EXCEPT all the columns, query should return an error |
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For the record, postgres rejects this syntax
postgres=# CREATE TABLE table1 (
a int,
b int,
c int,
d int
) ;
CREATE TABLE
postgres=# SELECT * EXCEPT(a, b, c, d)
FROM table1;
ERROR: syntax error at or near "a"
LINE 1: SELECT * EXCEPT(a, b, c, d)
^Thus I agree we should be following the duckdb behavior
memory D CREATE TABLE table1 (
a int,
b int,
c int,
d int
);However, duckdb seems to reject this syntax entirely
How did
memory D SELECT * EXCEPT a, b, c, d FROM table1;
Parser Error:
syntax error at or near "a"
LINE 1: SELECT * EXCEPT a, b, c, d FROM table1;
^
memory D SELECT * EXCEPT(a, b, c, d) FROM table1;
Parser Error:
syntax error at or near "a"
LINE 1: SELECT * EXCEPT(a, b, c, d) FROM table1;
^It looks like the actual syntax is EXCLUDE rather than EXCEPT...
memory D SELECT * EXCLUDE(a, b, c, d) FROM table1;
Binder Error:
SELECT list is empty after resolving * expressions!🤔
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(sorry I accidentally pushed to this branch -- i reverted the change) |
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@alamb Thank you for the review! Is there anything else I need to do? |
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Which issue does this PR close?
SELECT * EXCLUDE(...)silently returns empty rows when all columns are excluded #21258.Rationale for this change
When
SELECT * EXCLUDE(...)orSELECT * EXCEPT(...)excludes every column in the schema, DataFusion silently produces rows with zero columns instead of failing at planning time. This is confusing and inconsistent with DuckDB, which raises a clearBinder Error: SELECT list is empty after resolving * expressions!at planning time.What changes are included in this PR?
project_with_validation(builder.rs), after expanding allWildcardandQualifiedWildcardexpressions, added a check: if any wildcard was present and the resulting projection list is empty, return aplan_err!with the messageSELECT list is empty after resolving * expressions, the wildcard expanded to zero columns.statement ok) tostatement errorasserting the new error message. Cases updated include bareSELECT * EXCEPT(all_cols), withLIMIT,WHERE,GROUP BY,JOIN, and window functions.Are these changes tested?
Yes. The existing SQL logic tests in select.slt are updated to assert the new planning error for all zero-column wildcard scenarios (
EXCLUDEandEXCEPT, with various clauses). This covers:SELECT * EXCLUDE(a, b)/SELECT * EXCEPT(a, b, c, d)on a plain scanLIMIT,WHERE,GROUP BY,JOIN, and window functionsSELECT t.* EXCLUDE(...))Are there any user-facing changes?
Yes. Queries that previously silently returned empty-column result sets via
SELECT * EXCLUDE(...)orSELECT * EXCEPT(...)when all columns were excluded will now fail at planning time with: