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 |
思路:用异或
update salary set sex = CHAR(ASCII('f') ^ ASCII('m') ^ ASCII(sex));
Think of it as: 11 is the difference between 'm' and 'f'. (Like we said earlier, 11 = 'm' ^ 'f'.)这里是用asc码运算,'m'=01101101,'f'=01100110, 'm' ^ 'f'=00001011(十进制=11).
So now that we know the difference, it can be used to convert both an 'm' into an 'f' AND an 'f' into an 'm'.
So,
f = 'm' ^ 11; // This converts an 'm' into an 'f'.
m = 'f' ^ 11; // This converts an 'f' into an 'm'.
结论:f⊕m的结果为G,则通过变换可以得到对方:
f ⊕ G = m
m ⊕ G = f
