Commit 04e53d2
[SPAR-27342][SQL] Optimize Limit 0 queries
## What changes were proposed in this pull request?
With this change, unnecessary file scans are avoided in case of Limit 0 queries.
I added a case (rule) to `PropagateEmptyRelation` to replace `GlobalLimit 0` and `LocalLimit 0` nodes with an empty `LocalRelation`. This prunes the subtree under the Limit 0 node and further allows other rules of `PropagateEmptyRelation` to optimize the Logical Plan - while remaining semantically consistent with the Limit 0 query.
For instance:
**Query:**
`SELECT * FROM table1 INNER JOIN (SELECT * FROM table2 LIMIT 0) AS table2 ON table1.id = table2.id`
**Optimized Plan without fix:**
```
Join Inner, (id#79 = id#87)
:- Filter isnotnull(id#79)
: +- Relation[id#79,num1#80] parquet
+- Filter isnotnull(id#87)
+- GlobalLimit 0
+- LocalLimit 0
+- Relation[id#87,num2#88] parquet
```
**Optimized Plan with fix:**
`LocalRelation <empty>, [id#75, num1#76, id#77, num2#78]`
## How was this patch tested?
Added unit tests to verify Limit 0 optimization for:
- Simple query containing Limit 0
- Inner Join, Left Outer Join, Right Outer Join, Full Outer Join queries containing Limit 0 as one of their children
- Nested Inner Joins between 3 tables with one of them having a Limit 0 clause.
- Intersect query wherein one of the subqueries was a Limit 0 query.
Closes #24271 from aayushmaanjain/optimize-limit0.
Authored-by: Aayushmaan Jain <[email protected]>
Signed-off-by: gatorsmile <[email protected]>1 parent 0e44a51 commit 04e53d2
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- sql/catalyst/src
- main/scala/org/apache/spark/sql/catalyst/optimizer
- test/scala/org/apache/spark/sql/catalyst/optimizer
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