improved sql parser export parameter sharding support.

src/main/java/com/alibaba/druid/sql/dialect/mysql/visitor/MySqlOutputVisitor.java

@@ -158,10 +158,9 @@ public class MySqlOutputVisitor extends SQLASTOutputVisitor implements MySqlASTV
 
     {
         this.dbType = JdbcConstants.MYSQL;
+        this.shardingSupport = true;
     }
 
-    private boolean shardingSupport = true;
-
     public MySqlOutputVisitor(Appendable appender){
         super(appender);
     }