Github user HyukjinKwon commented on a diff in the pull request: https://github.com/apache/spark/pull/20787#discussion_r175985253 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/datetimeExpressions.scala --- @@ -1115,13 +1115,17 @@ case class AddMonths(startDate: Expression, numMonths: Expression) override def prettyName: String = "add_months" } - /** - * Returns number of months between dates date1 and date2. - */ + * Returns number of months between dates `timestamp1` and `timestamp2`. + * If `timestamp` is later than `timestamp2`, then the result is positive. + * If `timestamp1` and `timestamp2` are on the same day of month, or both + * are the last day of month, returns an integer (time of day will be ignored). + * Otherwise, the difference is calculated based on 31 days per month, and + * rounded to 8 digits. +*/ // scalastyle:off line.size.limit @ExpressionDescription( - usage = "_FUNC_(timestamp1, timestamp2) - Returns number of months between `timestamp1` and `timestamp2`.", + usage = "_FUNC_(timestamp1, timestamp2) - Returns number of months between `timestamp1` and `timestamp2`. Positive if `timestamp1` is later than `timestamp2`", --- End diff -- You could do either ```scala @ExpressionDescription( usage = """ _FUNC_(timestamp1, timestamp2) - blablabla blabla blabla """, ... ``` Let's add the description here too.
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