text: -- SQL Schema
  -- 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 = CASE WHEN sex = 'm' THEN 'f' 
      WHEN sex = 'f' THEN 'm'
      ELSE sex END
  