MySQL不能按某些指定的字段排序？

Question

I have a problem with sorting the results for the below codes. I have a dynamic sorting field whereby a certain value is met, it will sort by a specified field. However I can't seem to sort by some of the fields for some reasons and the result seems to sort by some unknown order... eg. i.totalExclTax - if I sort by this, the result is not sorted. Hence I was wondering why it can't sort by that field

SELECT
i.invoicedDateTime AS `(@datetime)Date`,
i.invoiceNum AS `Invoice Num`,
c.displayName AS `Customer Name`,
m.name AS `Membership`,
FORMAT(i.totalExclTax, 2) AS `Total (Excl Tax)`,
FORMAT( SUM(it.amount), 2 ) AS `Tax`,
FORMAT(i.totalInclTax, 2) AS `Total (Incl Tax)`
FROM
(smSales__invoice i
JOIN smCustomer__customer c ON(i.customerId = c.id)
   AND c.ts_Deleted IS NULL
     JOIN smCustomer__membership m ON (c.membershipId = m.id)
     AND m.ts_Deleted IS NULL
)
  JOIN smSales__invoiceTax it ON(it.invoiceId = i.id)
  AND it.ts_Deleted IS NULL
WHERE i.invoicedDateTime BETWEEN '2012-07-01 00:00:00' AND DATE_ADD('2012-08-31 00:00:00', INTERVAL 1 DAY)
AND i.invoicedOutletId IN ('230614c3761512c8db000a38a346e217')
AND i.type = 'sales'
AND i.voidedDateTime IS NULL
AND i.ts_Deleted IS NULL
GROUP BY i.id
ORDER BY
  CASE 'B'
    WHEN 'A' THEN i.invoiceNum
    WHEN 'B' THEN i.totalExclTax
    ELSE `Customer Name`
  END
ASC;

Answer 1

Your case always output the second value (i.totalExclTax) as a results as soon as 'B'='B' always. In MySQL try to use this equivalent of your statement:

ORDER BY 
if('B'='A', i.invoiceNum,if('B'='B',i.totalExclTax,'Customer Name')) 
ASC;