improved PageUtils & support natural join. issue #1711

src/main/java/com/alibaba/druid/sql/ast/statement/SQLJoinTableSource.java

@@ -29,6 +29,9 @@ public class SQLJoinTableSource extends SQLTableSourceImpl {
     protected SQLExpr             condition;
     protected final List<SQLExpr> using = new ArrayList<SQLExpr>();
 
+
+    protected boolean             natural = false;
+
     public SQLJoinTableSource(String alias){
         super(alias);
     }
@@ -93,6 +96,14 @@ public class SQLJoinTableSource extends SQLTableSourceImpl {
         return this.using;
     }
 
+    public boolean isNatural() {
+        return natural;
+    }
+
+    public void setNatural(boolean natural) {
+        this.natural = natural;
+    }
+
     public void output(StringBuffer buf) {
         this.left.output(buf);
         buf.append(' ');