Add solution 627 [sql]

if function()
case when .. then .. else .. end

Author: yanglbme

README.md

@@ -51,6 +51,7 @@ Complete [solutions](https://github.com/doocs/leetcode/tree/master/solution) to
 | 595 | [Big Countries](https://github.com/doocs/leetcode/tree/master/solution/595.Big%20Countries) | `SQL` |
 | 596 | [Classes More Than 5 Students](https://github.com/doocs/leetcode/tree/master/solution/596.Classes%20More%20Than%205%20Students) | `SQL` |
 | 605 | [Can Place Flowers](https://github.com/doocs/leetcode/tree/master/solution/605.Can%20Place%20Flowers) | `Array` |
+| 627 | [Swap Salary](https://github.com/doocs/leetcode/tree/master/solution/627.Swap%20Salary) | `SQL` |
 | 695 | [Max Area of Island](https://github.com/doocs/leetcode/tree/master/solution/695.Max%20Area%20of%20Island) | `Array`, `Depth-first Search` |
 | 703 | [Kth Largest Element in a Stream](https://github.com/doocs/leetcode/tree/master/solution/703.Kth%20Largest%20Element%20in%20a%20Stream) | `Heap` |
 | 707 | [Design Linked List](https://github.com/doocs/leetcode/tree/master/solution/707.Design%20Linked%20List) | `Linked List`, `Design` |

solution/627.Swap Salary/README.md

@@ -0,0 +1,47 @@
+## 交换工资
+### 题目描述
+
+给定一个 `salary` 表，如下所示，有m=男性 和 f=女性的值 。交换所有的 f 和 m 值(例如，将所有 f 值更改为 m，反之亦然)。要求使用一个更新查询，并且没有中间临时表。
+
+例如:
+```
+| id | name | sex | salary |
+|----|------|-----|--------|
+| 1  | A    | m   | 2500   |
+| 2  | B    | f   | 1500   |
+| 3  | C    | m   | 5500   |
+| 4  | D    | f   | 500    |
+```
+
+运行你所编写的查询语句之后，将会得到以下表:
+```
+| id | name | sex | salary |
+|----|------|-----|--------|
+| 1  | A    | f   | 2500   |
+| 2  | B    | m   | 1500   |
+| 3  | C    | f   | 5500   |
+| 4  | D    | m   | 500    |
+```
+
+### 解法
+使用 `if` 函数 或者 `case when .. then .. else ... end`。
+
+```sql
+# Write your MySQL query statement below
+# update salary
+# set sex = if(sex = 'm', 'f', 'm')
+
+update salary
+set sex = (case when sex = 'f' then 'm' else 'f' end)
+
+```
+
+#### Input
+```json
+{"headers":{"salary":["id","name","sex","salary"]},"rows":{"salary":[[1,"A","m",2500],[2,"B","f",1500],[3,"C","m",5500],[4,"D","f",500]]}}
+```
+
+#### Output
+```json
+{"headers":["id","name","sex","salary"],"values":[[1,"A","f",2500],[2,"B","m",1500],[3,"C","f",5500],[4,"D","m",500]]}
+```