mysql drop table if exists inside procedure

Question

I'm trying to apply a nested set model example with procedures. I've found many of them with this technique and in the process I've found a problem. Every time I call the procedure I get unknown table XXX. When I create the procedure I got no problem at all. The quick example:

CREATE PROCEDURE `sp_getRoleTree` (IN root INT)
  READS SQL DATA
BEGIN
    DECLARE rows SMALLINT DEFAULT 0;
    DROP TABLE IF EXISTS ROLE_TREE;
    CREATE TABLE ROLE_TREE (
        nodeID INT PRIMARY KEY
    ) ENGINE=HEAP;

    INSERT INTO ROLE_TREE VALUES (root);

    SELECT * FROM ROLE_TREE;
    DROP TABLE ROLE_TREE;
END;

So my question is, am I doing something wrong here (it's example code), can I disable the warning on the if exists if the code is fine? Is there a special looping inside the procedures that's causing these kind of warnings?

Answer 1

As a work around: try to truncate table instead of re-creating.

Do not use DROP TABLE/CREATE TABLE. Create this table once (or when you need it) and use TRUNCATE TABLE command.

Answer 2

MySQL generates a warning when using DROP TABLE IF EXISTS tbl; when the table does not exist. This can be confusing and perhaps counter intuitive, but it is the expected behavior.

From http://dev.mysql.com/doc/refman/5.5/en/drop-table.html

Use IF EXISTS to prevent an error from occurring for tables that do not exist. A NOTE is generated for each nonexistent table when using IF EXISTS. See Section 13.7.5.41, SHOW WARNINGS Syntax.

IF EXISTS prevents MySQL from throwing an error, which is nice, but it causes a warning if the table does not exist. There is not an option to suppress this warning.