How to I modify this t-sql query to return the maximum value for different column names?

Question

I have the following query:

SELECT
        [Rate],
        [RateMon],
        [RateTue],
        [RateWed],
        [RateThu],
        [RateFri],
        [Ra         


        

Answer 1

You can use something verbose like:

SELECT Rate,
  CASE 
    WHEN RateMon>=RateTue AND RateMon>=RateWed AND RateMon>=RateThu AND 
         RateMon>=RateFri AND RAteMon>=RateSat AND RateMon>=RateSun THEN RateMon
    WHEN RateTue>=RateMon AND RateTue>=RateWed AND RateTue>=RateThu AND 
         RateTue>=RateFri AND RateTue>=RateSat AND RateTue>=RateSun THEN RateTue
    WHEN RateWed>=RateMon AND RateWed>=RateTue AND RateWed>=RateThu AND 
         RateWed>=RateFri AND RateWed>=RateSat AND RateWed>=RateSun THEN RateWed
    WHEN RateThu>=RateMon AND RateThu>=RateTue AND RateThu>=RateWed AND 
         RateThu>=RateFri AND RateThu>=RateSat AND RateThu>=RateSun THEN RateThu
    WHEN RateFri>=RateMon AND RateFri>=RateTue AND RateFri>=RateWed AND 
         RateFri>=RateThu AND RateFri>=RateSat AND RateFri>=RateSun THEN RateFri
    WHEN RateSat>=RateMon AND RateSat>=RateTue AND RateSat>=RateWed AND 
         RateSat>=RateThu AND RateSat>=RateFri AND RateSat>=RateSun THEN RateSat
    WHEN RateSun>=RateMon AND RateSun>=RateTue AND RateSun>=RateWed AND 
         RateSun>=RateThu AND RateSun>=RateFri AND RateSun>=RateSat THEN RateSun
    END AS MaxRate 
FROM    
    [Room]    
WHERE    
    Id=@Id   

A lot of typing, but that's one possible answer. You can also do the following, which is slightly less typing:

SELECT Rate, MAX(Rates.Rate) AS MaxRate
  FROM    
    [Room], 
      (SELECT RateMon AS Rate FROM [Room] WHERE Id=@Id UNION
       SELECT RateTue AS Rate FROM [Room] WHERE Id=@Id UNION
       SELECT RateWed AS Rate FROM [Room] WHERE Id=@Id UNION
       SELECT RateThu AS Rate FROM [Room] WHERE Id=@Id UNION
       SELECT RateFri AS Rate FROM [Room] WHERE Id=@Id UNION
       SELECT RateSat AS Rate FROM [Room] WHERE Id=@Id UNION
       SELECT RateSun AS Rate FROM [Room] WHERE Id=@Id)
     AS Rates
  WHERE    
    Id=@Id   

Of course, the correct solution would be to normalize your database and make this moot, since a simple join and aggregate would be sufficient.