Github user gatorsmile commented on a diff in the pull request:
https://github.com/apache/spark/pull/19752#discussion_r153079959
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/conditionalExpressions.scala
---
@@ -141,14 +141,34 @@ case class If(predicate: Expression, trueValue:
Expression, falseValue: Expressi
}
/**
- * Abstract parent class for common logic in CaseWhen and CaseWhenCodegen.
+ * Case statements of the form "CASE WHEN a THEN b [WHEN c THEN d]* [ELSE
e] END".
+ * When a = true, returns b; when c = true, returns d; else returns e.
*
* @param branches seq of (branch condition, branch value)
* @param elseValue optional value for the else branch
*/
-abstract class CaseWhenBase(
+// scalastyle:off line.size.limit
+@ExpressionDescription(
+ usage = "CASE WHEN expr1 THEN expr2 [WHEN expr3 THEN expr4]* [ELSE
expr5] END - When `expr1` = true, returns `expr2`; else when `expr3` = true,
returns `expr4`; else returns `expr5`.",
+ arguments = """
+ Arguments:
+ * expr1, expr3 - the branch condition expressions should all be
boolean type.
+ * expr2, expr4, expr5 - the branch value expressions and else value
expression should all be
+ same type or coercible to a common type.
+ """,
+ examples = """
+ Examples:
+ > SELECT CASE WHEN 1 > 0 THEN 1 WHEN 2 > 0 THEN 2.0 ELSE 1.2 END;
+ 1
+ > SELECT CASE WHEN 1 < 0 THEN 1 WHEN 2 > 0 THEN 2.0 ELSE 1.2 END;
+ 2
+ > SELECT CASE WHEN 1 < 0 THEN 1 WHEN 2 < 0 THEN 2.0 ELSE null END;
--- End diff --
Could you double check Hive returns NULL in the following case?
> SELECT CASE WHEN 1 < 0 THEN 1 WHEN 2 < 0 THEN 2.0 END;
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