Essayez ceci :
SELECT myCol
FROM myTable
WHERE SUBSTRING(myCol, 1 , 1) >= 'A'
AND SUBSTRING(myCol, 1 , 1) <= 'Z'
AND SUBSTRING(myCol, 2 , 1) >= 'A'
AND SUBSTRING(myCol, 2 , 1) <= 'Z'
AND SUBSTRING(myCol, 3 , 1) >= '0'
AND SUBSTRING(myCol, 3 , 1) <= '9'