ueshin opened a new pull request, #48664:
URL: https://github.com/apache/spark/pull/48664
### What changes were proposed in this pull request?
Adds the following DataFrame APIs for subqueries to Spark Classic.
- `scalar()`
- `exists()`
Also, add `outer()` to `Column` to specify outer references.
#### Examples:
For the following tables `l` and `r`:
```py
>>> spark.table("l").printSchema()
root
|-- a: long (nullable = true)
|-- b: double (nullable = true)
>>> spark.table("r").printSchema()
root
|-- c: long (nullable = true)
|-- d: double (nullable = true)
```
```py
from pyspark.sql import functions as sf
spark.table("l").where(
sf.col("b")
< (
spark.table("r")
.where(sf.col("a").outer() == sf.col("c"))
.select(sf.max("d"))
.scalar()
)
)
spark.table("l").select(
"a",
(
spark.table("l")
.where(sf.col("a") == sf.col("a").outer())
.select(sf.sum("b"))
.scalar()
.alias("sum_b")
),
)
spark.table("l").where(
spark.table("r").where(sf.col("a").outer() == sf.col("c")).exists()
)
```
### Why are the changes needed?
Subquery APIs are missing in DataFrame API.
### Does this PR introduce _any_ user-facing change?
Yes, new DataFrame APIs for subqueries will be available.
### How was this patch tested?
Added the related tests.
### Was this patch authored or co-authored using generative AI tooling?
No.
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