mysql查询不正确的输出

Question

I've a mysql table of simple data like:

now when i execute this simple query:

SELECT MAX(cashback) as MAX, MIN(cashback) as MIN FROM pearlcashback_retailers_category WHERE retailer_id='32' AND cashback NOT LIKE '%\%'

it outputs:

and for this query:

SELECT MAX(cashback) as MAX, MIN(cashback) as MIN FROM pearlcashback_retailers_category WHERE retailer_id='32' AND cashback LIKE '%\%'

it outputs:

please, help me...

---

sql of the table & data:

CREATE TABLE IF NOT EXISTS `pearlcashback_retailers_category` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `retailer_id` int(11) NOT NULL,
  `category_id` int(11) NOT NULL,
  `cashback` varchar(20) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM  DEFAULT CHARSET=latin1 AUTO_INCREMENT=15 ;


INSERT INTO `pearlcashback_retailers_category` (`id`, `retailer_id`, `category_id`, `cashback`) VALUES
(1, 32, 17, '46%'),
(2, 32, 14, '40'),
(11, 4, 15, '27%'),
(9, 32, 15, '5'),
(8, 32, 7, '44%'),
(14, 3, 13, '1');

Answer 1

Your cashback column is VARCHAR which is a text type, therefore min(), max() etc all operate on alphabetical sorting (which is normal), therefore "b" > "aaaa", and of course "5" > "100".

Use the correct types.

Answer 2

You are sorting a VARCHAR column - cashback, string '5' is greater than string '40', in other words if you arrange '5' and '40' as in a dictionary, '5' comes after '40', hence ther result MAX - '5' and MIN '40',

In the other case - if you arrange '46%' and '44%' as in a dictionary, '46%' comes later than '44%', hence MAX '46%' and MIN '44%'

Answer 3

Your cashback field is incorrect. Data should be in one format. If you store in this field only percentages symbol % is not required. It will be good for your query and your architecture. Sorry for my english.

Answer 4

cashback seem to be a varchar column and for such '40' < '5' is true. I'm not sure if the following works with mysql:

SELECT MAX(cashback) as MAX, MIN(cashback) as MIN 
FROM pearlcashback_retailers_category 
WHERE retailer_id='32' AND cashback NOT LIKE '%\%'
ORDER BY cast(cashback as integer)