此SQL查询有什么问题？

Question

SELECT [travel], [fro_m], [t_o], [dep], [arr], [fare], [discount], [faresleeper],
[rating], [seats], [s_no],
[booking_closed] = 
   CASE WHEN s1from <= @date AND s1to >= @date THEN s1Rate ELSE fare END 
        WHEN s2from <= @date AND s2to >= @date THEN s2Rate ELSE fare END 
        WHEN s3rate <= @date AND s3to >= @date THEN s3Rate ELSE fare END 
FROM a1_volvo WHERE (fro_m = @fro_m) AND (t_o = @t_o)

Answer 1

The case statement is incorrect:

CASE WHEN s1from <= @date AND s1to >= @date THEN s1Rate 
WHEN s2from <= @date AND s2to >= @date THEN s2Rate 
WHEN s3rate <= @date AND s3to >= @date THEN s3Rate 
else fare END

You have and else statement after each line in the case statement. It should only be at the end.

MSDN Case Statement

Answer 2

In the third WHEN option you are comparing a field with name s3rate with a date .Well I dont know what these fields are but it seems to me that is not a date field...

Also have a look at Kevin & BobTodd answers for another catch...

Answer 3

CASE WHEN s1from <= @date AND s1to >= @date THEN s1Rate 
        WHEN s2from <= @date AND s2to >= @date THEN s2Rate 
        WHEN s3rate <= @date AND s3to >= @date THEN s3Rate 
    ELSE fare 
END 

is better?

Answer 4

This does the same as his code, but uses between and. They advantage of using it is, that it is better readabl. When doing code review you spare endless time compare whether two name are typed identical

 CASE WHEN @date between s1from AND s1to THEN s1Rate 
      WHEN @date between s2from AND s2to THEN s2Rate 
      WHEN @date between s3rate AND s3to THEN s3Rate 
      ELSE fare 
END