corrected case when expressions

Author: wumpz

README.md

@@ -44,7 +44,9 @@ To help JSqlParsers development you are encouraged to provide
 Also I would like to know about needed examples or documentation stuff.
 
 ## Extensions in the latest SNAPSHOT version 0.9.8
-
+* support for simple expressions within case when
+* rewrite of SelectBody - production, reduce of needed lookaheads results in huge parser performance improvement
+  * please test it due to possible changes in the parse tree
 
 ## Extensions of JSqlParser releases
 

src/main/jjtree/net/sf/jsqlparser/parser/JSqlParserCC.jjt

@@ -1683,7 +1683,6 @@ Expression AndExpression() :
 	{ result = left; }
 
 	(
-		LOOKAHEAD(<K_AND>)
  		<K_AND>
 		(
 		LOOKAHEAD(Condition())
@@ -2444,12 +2443,11 @@ Expression CaseWhenExpression() #CaseWhenExpression:
 	<K_CASE>
 	(
     	    ( clause=WhenThenSearchCondition() { whenClauses.add(clause); } )+
-             [<K_ELSE> elseExp=SimpleExpression()]
 		|
 		    (LOOKAHEAD(RegularCondition()) switchExp=RegularCondition() | switchExp=BitwiseAndOr())
              ( clause=WhenThenValue() { whenClauses.add(clause); } )+
-             [<K_ELSE> elseExp=SimpleExpression()]
 	)
+   [<K_ELSE> elseExp=SimpleExpression()]
     <K_END>
     {
     	caseExp.setSwitchExpression(switchExp);
@@ -2466,7 +2464,7 @@ WhenClause WhenThenSearchCondition():
 	Expression thenExp = null;
 }
 {
-	<K_WHEN> whenExp=Expression() <K_THEN> thenExp=SimpleExpression()
+	<K_WHEN> (LOOKAHEAD(Expression()) whenExp=Expression() | whenExp=SimpleExpression()) <K_THEN> thenExp=SimpleExpression()
 	{
 	   whenThen.setWhenExpression(whenExp);
 	   whenThen.setThenExpression(thenExp);

src/test/java/net/sf/jsqlparser/test/select/SelectTest.java

@@ -1099,6 +1099,14 @@ public void testIssue371SimplifiedCase() throws JSQLParserException {
     public void testIssue371SimplifiedCase2() throws JSQLParserException {
         assertSqlCanBeParsedAndDeparsed("SELECT CASE col > 4 WHEN true THEN 1 ELSE 0 END");
     }
+    
+    public void testIssue235SimplifiedCase3() throws JSQLParserException {
+        assertSqlCanBeParsedAndDeparsed("SELECT CASE WHEN (CASE WHEN (CASE WHEN (1) THEN 0 END) THEN 0 END) THEN 0 END FROM a");
+    }
+    
+    public void testIssue235SimplifiedCase4() throws JSQLParserException {
+        assertSqlCanBeParsedAndDeparsed("SELECT CASE WHEN (CASE WHEN (CASE WHEN (CASE WHEN (1) THEN 0 END) THEN 0 END) THEN 0 END) THEN 0 END FROM a");
+    }
 
     public void testReplaceAsFunction() throws JSQLParserException {
         String statement = "SELECT REPLACE(a, 'b', c) FROM tab1";