Minor Description
According to the SQL standard, date1 - date2 is an interval. See http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt at 4.5.3 Operations involving datetimes and intervals. The ticket aims to modify the DateDiff expression to produce another expression of the INTERVAL type When wspark.sql.ansi.enabled` is set to true and `spark.sql.dialect` is Spark.