Github user liancheng commented on a diff in the pull request:
https://github.com/apache/spark/pull/2678#discussion_r18468334
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/SqlParser.scala ---
@@ -333,6 +338,24 @@ class SqlParser extends StandardTokenParsers with
PackratParsers {
IF ~> "(" ~> expression ~ "," ~ expression ~ "," ~ expression <~ ")"
^^ {
case c ~ "," ~ t ~ "," ~ f => If(c,t,f)
} |
+ CASE ~> opt(expression) ~ (WHEN ~ expression ~ THEN ~ expression).* ~
+ opt(ELSE ~> expression) <~ END ^^ {
+ case c ~ l ~ el =>
+ var caseWhenExpr = l.map{x =>
+ x match {
+ case w ~ we ~ t ~ te =>
+ c match {
+ case Some(e) => Seq(EqualTo(e, we), te)
+ case None => Seq(we, te)
+ }
+ }
+ }.toSeq.reduce(_ ++ _)
+ caseWhenExpr = el match {
+ case Some(e) => caseWhenExpr ++ Seq(e)
+ case None => caseWhenExpr
+ }
+ CaseWhen(caseWhenExpr)
+ } |
--- End diff --
Haven't tested yet, but I think this parser can be simplified to:
```scala
CASE ~> expression.? ~ (WHEN ~> expression ~ (THEN ~> expression)).* ~
(ELSE ~> expression).? <~ END ^^ {
case casePart ~ alternatives ~ elsePart =>
val alternativesPart= alternatives.flatMap { case whenExpr ~
thenExpr =>
casePart.fold(whenExpr)(EqualTo(_, whenExpr)) :: thenExpr :: Nil
}
CaseWhen(alternativesPart ++ elsePart.toList)
}
```
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