Add support for functions in an interval expression (#1099)

Author: tomershay

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

@@ -3498,7 +3498,7 @@ IntervalExpression IntervalExpression() : {
 {
 
 { interval = new IntervalExpression(); }
-    <K_INTERVAL> ["-" {signed=true;}] (token=<S_LONG> | token=<S_DOUBLE> | token=<S_CHAR_LITERAL> | expr = Column() | expr = JdbcNamedParameter() | expr = SimpleJdbcParameter() )
+    <K_INTERVAL> ["-" {signed=true;}] (token=<S_LONG> | token=<S_DOUBLE> | token=<S_CHAR_LITERAL> | LOOKAHEAD(SimpleJdbcParameter()) expr = SimpleJdbcParameter() | expr = JdbcNamedParameter() | LOOKAHEAD(Function()) expr = Function() | expr = Column())
     {
         if (expr != null) {
             if (signed) expr = new SignedExpression('-', expr);

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

@@ -2308,6 +2308,12 @@ public void testIntervalWithColumn() throws JSQLParserException {
         assertSqlCanBeParsedAndDeparsed(stmt);
     }
 
+    @Test
+    public void testIntervalWithFunction() throws JSQLParserException {
+        String stmt = "SELECT DATE_ADD(start_date, INTERVAL COALESCE(duration, 21) MINUTE) AS end_datetime FROM appointment";
+        assertSqlCanBeParsedAndDeparsed(stmt);
+    }
+
     @Test
     public void testInterval1() throws JSQLParserException {
         String stmt = "SELECT 5 + INTERVAL '3 days'";