MySQL order by簡単解析

MySQL order by簡単解析
1.文

SELECT distinct first_letter
FROM tb_customer
WHERE (deleted = 0) ORDER BY first_letter = '#' asc,first_letter;

2.個人的な理解
order by first_letter='#'はfirst_を判断することに相当します.letter == "#"? 1 : 0;
3.SQL完全書き方

SELECT distinct first_letter
FROM tb_customer
WHERE (deleted = 0) ORDER BY if(first_letter = '#',1,0) asc,first_letter asc;

4.結果
ABCDEFGHIJKLMNOP