Define search depth, user variables, etc.

The user variable is to be defined after the cursor, or it will be an error:

Right: After the cursor is defined, otherwise the error is incorrect.

DECLARE cur1 cursor FOR select a.id,a.topic_id from Diz_reply as a where a.topic_id=topicid and a.parent_id= ' 0 ';
DECLARE continue HANDLER for SQLSTATE ' 02000 ' set replyid=null;
Set @num = 0;

Define system variables, search for depth, define the cursor, or error:

The correct approach is:

DECLARE parent_id VARCHAR (32);
Declare cur1 CURSOR for SELECT a.id,a.topic_id,a.parent_id from Reply_test as a where a.parent_id=pid;
Declare CONTINUE HANDLER for SQLSTATE ' 02000 ' SET iid = null;
SET @ @max_sp_recursion_depth = 99;
if (layer>0) THEN