## What changes were proposed in this pull request?
Since Spark 2.2.0 ([SPARK-19678](https://issues.apache.org/jira/browse/SPARK-19678)), the below SQL changed from `broadcast join` to `sort merge join`:
```sql
-- small external table with incorrect statistics
CREATE EXTERNAL TABLE t1(c1 int)
ROW FORMAT SERDE 'org.apache.hadoop.hive.ql.io.parquet.serde.ParquetHiveSerDe'
WITH SERDEPROPERTIES (
'serialization.format' = '1'
)
STORED AS
INPUTFORMAT 'org.apache.hadoop.hive.ql.io.parquet.MapredParquetInputFormat'
OUTPUTFORMAT 'org.apache.hadoop.hive.ql.io.parquet.MapredParquetOutputFormat'
LOCATION 'file:///tmp/t1'
TBLPROPERTIES (
'rawDataSize'='-1', 'numFiles'='0', 'totalSize'='0', 'COLUMN_STATS_ACCURATE'='false', 'numRows'='-1'
);
-- big table
CREATE TABLE t2 (c1 int)
LOCATION 'file:///tmp/t2'
TBLPROPERTIES (
'rawDataSize'='23437737', 'numFiles'='12222', 'totalSize'='333442230', 'COLUMN_STATS_ACCURATE'='false', 'numRows'='443442223'
);
explain SELECT t1.c1 FROM t1 INNER JOIN t2 ON t1.c1 = t2.c1;
```
This pr add a test case for this behavior change.
## How was this patch tested?
unit tests
Closes#24003 from wangyum/SPARK-19678.
Authored-by: Yuming Wang <yumwang@ebay.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>
43dcb91a4c