04e53d2e3c
## 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 <aayushmaan.jain42@gmail.com>
Signed-off-by: gatorsmile <gatorsmile@gmail.com>
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| .. | ||
| catalyst | ||
| core | ||
| hive | ||
| hive-thriftserver | ||
| create-docs.sh | ||
| gen-sql-markdown.py | ||
| mkdocs.yml | ||
| README.md | ||
Spark SQL
This module provides support for executing relational queries expressed in either SQL or the DataFrame/Dataset API.
Spark SQL is broken up into four subprojects:
- Catalyst (sql/catalyst) - An implementation-agnostic framework for manipulating trees of relational operators and expressions.
- Execution (sql/core) - A query planner / execution engine for translating Catalyst's logical query plans into Spark RDDs. This component also includes a new public interface, SQLContext, that allows users to execute SQL or LINQ statements against existing RDDs and Parquet files.
- Hive Support (sql/hive) - Includes an extension of SQLContext called HiveContext that allows users to write queries using a subset of HiveQL and access data from a Hive Metastore using Hive SerDes. There are also wrappers that allow users to run queries that include Hive UDFs, UDAFs, and UDTFs.
- HiveServer and CLI support (sql/hive-thriftserver) - Includes support for the SQL CLI (bin/spark-sql) and a HiveServer2 (for JDBC/ODBC) compatible server.
Running sql/create-docs.sh generates SQL documentation for built-in functions under sql/site.