text: /*
  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 statement and no intermediate temp table.
  Note that you must write a single update statement, 
  DO NOT write any select statement for this problem.
  Example:
  | id | name | sex | salary |
  |----|------|-----|--------|
  | 1  | A    | m   | 2500   |
  | 2  | B    | f   | 1500   |
  | 3  | C    | m   | 5500   |
  | 4  | D    | f   | 500    |
  After running your update statement, 
  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    |
  */
  UPDATE Salary
  set sex = IF(sex = 'f', 'm', 'f')