SELECT id where min or max value from multiple columns - php

Question

I'm looking for a fast MySQL query that returns the id of the product with the lowest (min) or highest (max) price, compared to all price categories (a, b, c and d).
I have a product table called chocolate_stock with several price categories. It's pretty easy to receive the lowest (min) or highest (max) price from a specific category (a or b or c or d).
id | name | price_a | price_b | price_c | price_d |
--------------------------------------------------------------
1 | Chips Ahoy | 250 | 530 | 720 | 120
--------------------------------------------------------------
2 | Chocolate Chunk | 250 | 90 | 32.92 | 110
--------------------------------------------------------------
3 | Oreo | 103 | 44.52 | 250 | 850
--------------------------------------------------------------
The price categories are decimal(10,2). Here's a sample that returns the highest price from the categories, but not the id:
$t = 'chocolate_stock';
$arrIds = array(1, 3);
$strQuery = "SELECT id,
MAX(price_a) AS price_a,
MAX(price_b) AS price_b,
MAX(price_c) AS price_c,
MAX(price_d) AS price_d
FROM $t WHERE id IN(". implode(',', array_map('intval', $arrIds)) .")";
What is the fastest way to retrieve this information?

Answer 1

This query does what you want:
(select t.*
from $t t
where . . .
order by price_a desc
limit 1) union all
(select t.*
from $t t
where . . .
order by price_b desc
limit 1) union all
(select t.*
from $t t
where . . .
order by price_c desc
limit 1) union all
(select t.*
from $t t
where . . .
order by price_d desc
limit 1)
If you have an index on id it should perform reasonably well.
That approach requires four passes through the table (although the index on id should greatly reduce that). The following approach requires only one pass through the table:
select MAX(price_a),
substring_index(group_concat(id order by price_a desc), ',', 1),
max(price_b),
substring_index(group_concat(id order by price_b desc), ',', 1),
max(price_c),
substring_index(group_concat(id order by price_c desc), ',', 1),
max(price_d),
substring_index(group_concat(id order by price_d desc), ',', 1)
from $t
where . . .
It uses a trick with group_concat() and substring_index() to get the max id for each of the columns.

Answer 2

It might help if you were to tabulate what you want your output to look like, but I think the piece you are missing is the HAVING clause.
first - try this
select min(id), max(price_a) from $t having price_a = max(price_a)
Then try
select min(id), min(price_a) from $t having price_a = min(price_a)
union
select min(id), max(price_a) from $t having price_a = max(price_a)

Answer 3

The first thing you would want to do is normalise your data, for ease of later querying I would create the following view:
CREATE VIEW NormalT
AS
SELECT ID, Name, 'Price_a' AS Type, Price_a AS Price
FROM T
UNION ALL
SELECT ID, Name, 'Price_b' AS Type, Price_b AS Price
FROM T
UNION ALL
SELECT ID, Name, 'Price_c' AS Type, Price_c AS Price
FROM T
UNION ALL
SELECT ID, Name, 'Price_d' AS Type, Price_d AS Price
FROM T;
Then I am not sure of the format you want, if you want the min an max for each price you could use this:
SELECT mt.Type2,
mt.Type,
mt.Price,
t.ID,
t.Name
FROM ( SELECT Type, MIN(Price) AS Price, 'MIN' AS Type2
FROM NormalT
GROUP BY Type
UNION ALL
SELECT Type, MAX(Price) AS Price, 'MAX' AS Type2
FROM NormalT
GROUP BY Type
) mt
INNER JOIN NormalT T
ON mt.Type = T.Type
AND mt.Price = t.Price
ORDER BY mt.Type2, mt.Type, t.ID;
Which will output the following from your sample data:
TYPE2 TYPE PRICE ID NAME
MAX Price_a 250 1 Chips Ahoy
MAX Price_a 250 2 Chocolate Chunk
MAX Price_b 530 1 Chips Ahoy
MAX Price_c 720 1 Chips Ahoy
MAX Price_d 850 3 Oreo
MIN Price_a 103 3 Oreo
MIN Price_b 44.52 3 Oreo
MIN Price_c 32.92 2 Chocolate Chunk
MIN Price_d 110 2 Chocolate Chunk
However, if it is just the min and max of all prices (a, b, c and d) then you could use this:
SELECT mt.Type2,
t.Type,
mt.Price,
t.ID,
t.Name
FROM ( SELECT MIN(Price) AS Price, 'MIN' AS Type2
FROM NormalT
UNION ALL
SELECT MAX(Price) AS Price, 'MAX' AS Type2
FROM NormalT
) mt
INNER JOIN NormalT T
ON mt.Price = t.Price;
Which will output this:
TYPE2 TYPE PRICE ID NAME
MIN Price_c 32.92 2 Chocolate Chunk
MAX Price_d 850 3 Oreo
Examples on SQL Fiddle

Answer 4

Try this , It's emulating Analytics as MYSQL doesn't have them by default :
SELECT id,
( select MAX(price_a) from $t t2 where t2.id = t1.id ) AS price_a,
( select MAX(price_b) from $t t2 where t2.id = t1.id ) AS price_b,
( select MAX(price_c) from $t t2 where t2.id = t1.id ) AS price_c,
( select MAX(price_d) from $t t2 where t2.id = t1.id ) AS price_d
FROM $t t1 WHERE id IN(". implode(',', array_map('intval', $arrIds)) .")
Source From : http://www.oreillynet.com/pub/a/mysql/2007/03/29/emulating-analytic-aka-ranking-functions-with-mysql.html?page=3

Answer 5

You are not getting id because, MAX returns one value. But it is not so with id.You can use seperate queries like
SELECT id,MAX(price_a) FROM $t WHERE id IN (". implode(',', array_map('intval', $arrIds)).")";
SELECT id,MAX(price_b) FROM $t WHERE id IN (". implode(',', array_map('intval', $arrIds)).")";
etc