Given a table salary, such as the one below, that has m=male and f=female values. Swap all f and m values (i.e., change all f values to m and vice versa) with a single update query and no intermediate temp table.
For example:
| id | name | sex | salary |
|----|------|-----|--------|
| 1 | A | m | 2500 |
| 2 | B | f | 1500 |
| 3 | C | m | 5500 |
| 4 | D | f | 500 |
After running your query, the above salary table should have the following rows:
| id | name | sex | salary |
|----|------|-----|--------|
| 1 | A | f | 2500 |
| 2 | B | m | 1500 |
| 3 | C | f | 5500 |
| 4 | D | m | 500 |
sql：
create table if not exists salary(id int, name varchar(100), sex char(1), salary int);
Truncate table salary;
insert into salary (id, name, sex, salary) values ('1', 'A', 'm', '2500');
insert into salary (id, name, sex, salary) values ('2', 'B', 'f', '1500');
insert into salary (id, name, sex, salary) values ('3', 'C', 'm', '5500');
insert into salary (id, name, sex, salary) values ('4', 'D', 'f', '500');
Swap all f and m values (i.e., change all f values to m and vice versa) with a single update query and no intermediate temp table.
最后一句 and no intermediate temp table 没有中间临时表进行交换
我直接全段翻译的结果是：
坑。。。
解题：
1 . update salary set sex = case when sex='m' then 'f' else 'm' end
2 . update salary set sex = if(sex = 'f','m','f');
