bug fixed for sql parser for postgresql, for issue 1204, https://github.com/alibaba/druid/issues/1204

src/main/java/com/alibaba/druid/sql/dialect/postgresql/parser/PGExprParser.java

@@ -65,6 +65,10 @@ public class PGExprParser extends SQLExprParser {
         }
         return super.parseDataType();
     }
+    
+    public PGSelectParser createSelectParser() {
+        return new PGSelectParser(this);
+    }
 
     public SQLExpr primary() {
         if (lexer.token() == Token.ARRAY) {