Sorting DB Results

I am trying to write a query (mysql 3.23) that will sort results using one or two substrings in item number. So for example I have item numbers that start with SE0000, TS0000, N00000, W000000, etc. So let say I want results sorted in the following order TS0000, SE0000, N00000, W00000 I have tried the following in my query but it's not sorting properly: ORDER BY FIELD(LEFT(item_number, 2) , 'TS'), FIELD(LEFT(item_number, 1) 'N','W') So my question is, should I put results in an array, then sort the array instead of trying to sort from mysql?