Converting text column to integer in MySQL
===

I'm trying to create a cleaned-up table that replaces a varchar(50) field with an integer.  The original field has occasional text values that I'd like to convert to 0 or <NULL> values.
I can do this in a select statement just fine, but get an error when trying to create my table.

Below is a minimal example that uses strings:

    /* This works */
    DROP TABLE IF EXISTS mytest;
    CREATE TABLE mytest
    AS
       SELECT convert("123", unsigned) AS mynum;
     
    /* This works, returning a row of 0 */
    SELECT convert("TEST", unsigned) AS mynum;
     
    /* But this fails, with:  Truncated incorrect INTEGER value: 'TEST'*/
    DROP TABLE IF EXISTS mytest;
    CREATE TABLE mytest
    AS
       SELECT convert("TEST", unsigned) AS mynum;`
 
What is wrong with the above, and is there a better way to accomplish what I want?  Thanks for the help.