add leetcode problem-cn part3

算法题（国内版）/problem (English)/变更性别(English) [swap-salary].html

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+<p>Table: <code>Salary</code></p>
+
+<pre>
++-------------+----------+
+| Column Name | Type     |
++-------------+----------+
+| id          | int      |
+| name        | varchar  |
+| sex         | ENUM     |
+| salary      | int      |
++-------------+----------+
+id is the primary key for this table.
+The sex column is ENUM value of type (&#39;m&#39;, &#39;f&#39;).
+The table contains information about an employee.
+</pre>
+
+<p>&nbsp;</p>
+
+<p>Write an SQL query to swap all <code>&#39;f&#39;</code> and <code>&#39;m&#39;</code> values (i.e., change all <code>&#39;f&#39;</code> values to <code>&#39;m&#39;</code> and vice versa) with a <strong>single update statement</strong> and no intermediate temporary tables.</p>
+
+<p>Note that you must write a single update statement, <strong>do not</strong> write any select statement for this problem.</p>
+
+<p>The query result format is in the following example.</p>
+
+<p>&nbsp;</p>
+<p><strong>Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> 
+Salary table:
++----+------+-----+--------+
+| id | name | sex | salary |
++----+------+-----+--------+
+| 1  | A    | m   | 2500   |
+| 2  | B    | f   | 1500   |
+| 3  | C    | m   | 5500   |
+| 4  | D    | f   | 500    |
++----+------+-----+--------+
+<strong>Output:</strong> 
++----+------+-----+--------+
+| id | name | sex | salary |
++----+------+-----+--------+
+| 1  | A    | f   | 2500   |
+| 2  | B    | m   | 1500   |
+| 3  | C    | f   | 5500   |
+| 4  | D    | m   | 500    |
++----+------+-----+--------+
+<strong>Explanation:</strong> 
+(1, A) and (3, C) were changed from &#39;m&#39; to &#39;f&#39;.
+(2, B) and (4, D) were changed from &#39;f&#39; to &#39;m&#39;.
+</pre>