DMS无法成功执行下列sql

/*DMS无法成功执行下列sql，但在Navicat for MySQL是可以执行成功的，我mysql版本为5.6。不知是什么原因*/
/*这段sql是添加索引时使用*/


drop procedure if exists dlt_idx;
create procedure dlt_idx(in p_tblName varchar(128), in p_idxName varchar(128))
begin
   declare str varchar(256);
   declare cnt int;
   declare currnet_schema varchar(64);
   if p_idxName='PRIMARY' then
       set @str = concat('alter table ', p_tblName, ' drop primary key;');
   else
       set @str = concat('drop index ', p_idxName, ' on ', p_tblName, ';');
   end if;
   select schema() into @current_schema;
   select count(*) into @cnt from information_schema.statistics
   where table_name=p_tblName and index_name=p_idxName;
   if @cnt>0 then
       prepare stmt from @str;
       execute stmt;
   end if;
end;


/*************************************************/

/*事实上DMS边下面代码都无法执行！！！*/

create procedure dlt_idx(in p_tblName varchar(128), in p_idxName varchar(128)) begin
   declare str varchar(256);    declare cnt int;
end;