Adding support for simple expressions in INTERVAL expressions (#910)

Author: tomershay

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

@@ -3102,7 +3102,7 @@ IntervalExpression IntervalExpression() : {
 {
 
 { interval = new IntervalExpression(); }
-    <K_INTERVAL> ["-" {signed=true;}] (token=<S_LONG> | token=<S_DOUBLE> | token=<S_CHAR_LITERAL> | expr = Column()) 
+    <K_INTERVAL> ["-" {signed=true;}] (token=<S_LONG> | token=<S_DOUBLE> | token=<S_CHAR_LITERAL> | expr = SimpleExpression())
     { 
         if (expr != null) {
             if (signed) expr = new SignedExpression('-', expr);

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

@@ -1322,6 +1322,11 @@ public void testIssue862CaseWhenConcat() throws JSQLParserException {
         assertSqlCanBeParsedAndDeparsed("SELECT c1, CASE c1 || c2 WHEN '091' THEN '2' ELSE '1' END AS c11 FROM T2");
     }
 
+    @Test
+    public void testExpressionsInIntervalExpression() throws JSQLParserException {
+        assertSqlCanBeParsedAndDeparsed("SELECT DATE_SUB(mydate, INTERVAL DAY(anotherdate) - 1 DAY) FROM tbl");
+    }
+
     @Test
     public void testReplaceAsFunction() throws JSQLParserException {
         String statement = "SELECT REPLACE(a, 'b', c) FROM tab1";