选择具有最大值的唯一行（有条件）

Question

With the table and data below I am trying to get the highest effective_from values that are less than the current timestamp, per unique brand / model combination - effectively the current price per item.

CREATE TABLE things
(`id` int, `brand` varchar(1), `model` varchar(5), `effective_from` int, `price` int);

INSERT INTO things
(`id`, `brand`, `model`, `effective_from`, `price`)
VALUES
(1, 'a', 'red', 1402351200, 100),
(2, 'b', 'red', 1402351200, 110),
(3, 'a', 'green', 1402391200, 120),
(4, 'b', 'blue', 1402951200, 115),
(5, 'a', 'red', 1409351200, 150),
(6, 'a', 'blue', 1902351200, 140),
(7, 'b', 'green', 1402358200, 135),
(8, 'b', 'blue', 1902358200, 155),
(9, 'b', 'red', 1902751200, 200),
(10, 'a', 'red', 1908351200, 210),
(11, 'a', 'red', 1402264800, 660);

So far I have managed to get the row I'm looking for when I add conditions for a specific brand / model combination, but don't know how to fetch the current prices for all unique row combinations.

SELECT *
FROM things
WHERE effective_from<UNIX_TIMESTAMP()
AND brand='a'
AND model='red'
ORDER BY effective_from DESC
LIMIT 1;

If the current timestamp was 1402404432 the results should be as follows:

(1, 'a', 'red', 1402351200, 100),
(3, 'a', 'green', 1402391200, 120),
(2, 'b', 'red', 1402351200, 110),
(7, 'b', 'green', 1402358200, 135),

Answer 1

I guess you're after this. Advise if otherwise...

SELECT x.*
  FROM things x
  JOIN 
     ( SELECT brand
            , model
            , MAX(effective_from) max_effective_from 
         FROM things 
        WHERE effective_from <= UNIX_TIMESTAMP() 
        GROUP 
           BY brand
            , model
     ) y 
    ON y.brand = x.brand 
   AND y.model = x.model 
   AND y.max_effective_from = x.effective_from;
+------+-------+-------+----------------+-------+
| id   | brand | model | effective_from | price |
+------+-------+-------+----------------+-------+
|    1 | a     | red   |     1402351200 |   100 |
|    2 | b     | red   |     1402351200 |   110 |
|    3 | a     | green |     1402391200 |   120 |
|    7 | b     | green |     1402358200 |   135 |
+------+-------+-------+----------------+-------+

SELECT UNIX_TIMESTAMP();
+------------------+
| UNIX_TIMESTAMP() |
+------------------+
|       1402404432 |
+------------------+