MySQL에서 세션 변수가 처음 나타나는 경우에만 검색/바꾸기를 수행합니다.

mysql> set @Sentence='Thks ks is a my string';
Query OK, 0 rows affected (0.00 sec)

mysql> select @Sentence as NewString ,CONCAT(REPLACE(LEFT(@Sentence,
INSTR(@Sentence, 'k')), 'k', 'i'),
   -> SUBSTRING(@Sentence, INSTR(@Sentence, 'k') + 1)) as ChangeOnlyOneTime;

+------------------------+------------------------+
| NewString              | ChangeOnlyOneTime      |
+------------------------+------------------------+
| Thks ks is a my string | This ks is a my string |
+------------------------+------------------------+
1 row in set (0.00 sec)