zhengruifeng opened a new pull request, #38917:
URL: https://github.com/apache/spark/pull/38917
### What changes were proposed in this pull request?
correct the output column name of `groupBy.agg(count_distinct)`
### Why are the changes needed?
before this PR: `[id: bigint, count(value): bigint]`
```
scala> val df = spark.range(1, 10).withColumn("value", lit(1))
df: org.apache.spark.sql.DataFrame = [id: bigint, value: int]
scala> df.select(count_distinct($"value"))
res0: org.apache.spark.sql.DataFrame = [count(DISTINCT value): bigint]
scala> df.groupBy("id").agg(count_distinct($"value"))
res1: org.apache.spark.sql.DataFrame = [id: bigint, count(value): bigint]
scala> df.select(sum_distinct($"value"))
res2: org.apache.spark.sql.DataFrame = [sum(DISTINCT value): bigint]
scala> df.groupBy("id").agg(sum_distinct($"value"))
res3: org.apache.spark.sql.DataFrame = [id: bigint, sum(DISTINCT value):
bigint]
scala> df.createOrReplaceTempView("table")
scala> spark.sql(" SELECT id, COUNT(DISTINCT value) FROM table GROUP BY id ")
res5: org.apache.spark.sql.DataFrame = [id: bigint, count(DISTINCT value):
bigint]
```
after this PR: `[id: bigint, count(DISTINCT value): bigint]`
```
scala> val df = spark.range(1, 10).withColumn("value", lit(1))
df: org.apache.spark.sql.DataFrame = [id: bigint, value: int]
scala> df.select(count_distinct($"value"))
res0: org.apache.spark.sql.DataFrame = [count(DISTINCT value): bigint]
scala> df.groupBy("id").agg(count_distinct($"value"))
res1: org.apache.spark.sql.DataFrame = [id: bigint, count(DISTINCT value):
bigint]
```
### Does this PR introduce _any_ user-facing change?
the default column name changed
### How was this patch tested?
added UT
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