mysql> select * from contact;
+------+------+--------+--------+
| id | name | num | gender |
+------+------+--------+--------+
| 1 | 王大 | 202101 | 1 |
| 2 | 王二 | 202102 | 1 |
| 3 | 张三 | 202103 | 1 |
| 4 | 李四 | 202104 | 1 |
| 5 | 雷五 | 202105 | 1 |
| 6 | 大妞 | 202106 | 2 |
| 7 | 二妞 | 202107 | 2 |
| 8 | 刘备 | 202108 | 1 |
+------+------+--------+--------+
8 rows in set (0.00 sec)
mysql> select id,name,num
-> case gender
-> when '1' then '4'
-> when '2' then '5’
'> end
'> from contact;
