在刷LeetCode的時候遇到的SQL題目

627. Swap Salary

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    |

大概就是要求交換表中sex列的性別

一開始想著用update salary set sex = f when sex = m再用個AND，後來一想這樣執行的結果應該是錯的、

然後就偷看了solution，才知道還有when case語句，所以記錄一下

update salary  
set sex =   
    case sex  
        when ‘m‘ then ‘f‘  
        else ‘m‘  
    end; 

大概意思就是when m，then就設置為f，，else都設置為m

SQL交換一列中數據的值（如男女性別）