在不同的列基于价值的MySQL选择增量指标

Question

我做下面的SELECT

SELECT products.supplier_catalog_number, prices.price, 0 AS price_index 
FROM products 
    INNER JOIN prices ON prices.product_id = products.id 
LIMIT 10 

，结果看起来像

+-------------------------+----------+-------------+ 
| supplier_catalog_number | price | price_index | 
+-------------------------+----------+-------------+ 
| 00000001600L   | 287.0000 |   0 | 
| 00000001600L   | 243.9500 |   0 | 
| 0023-200    | 710.0000 |   0 | 
| 0023-200    | 603.5000 |   0 | 
| 0023-300    | 232.0000 |   0 | 
| 0023-300    | 185.6000 |   0 | 
| 0023-301    | 289.0000 |   0 | 
| 0023-301    | 231.2000 |   0 | 
| 0023-301    | 109.0000 |   0 | 
| 0023-301    | 92.6500 |   0 | 
+-------------------------+----------+-------------+ 

我需要的结果是

+-------------------------+----------+-------------+ 
| supplier_catalog_number | price | price_index | 
+-------------------------+----------+-------------+ 
| 00000001600L   | 287.0000 |   0 | 
| 00000001600L   | 243.9500 |   1 | 
| 0023-200    | 710.0000 |   0 | 
| 0023-200    | 603.5000 |   1 | 
| 0023-300    | 232.0000 |   0 | 
| 0023-300    | 185.6000 |   1 | 
| 0023-301    | 289.0000 |   0 | 
| 0023-301    | 231.2000 |   1 | 
| 0023-301    | 109.0000 |   2 | 
| 0023-301    | 92.6500 |   3 | 
+-------------------------+----------+-------------+ 

可以在单个查询中完成吗？

Answer 1

理想情况下，你可以通过12.19 Window Functions来实现你所需要的，但是MySQL目前没有官方的支持。

例如，在MariaDB的（> = 10.2.0），Window Functions，可以运行下面这样的查询：

SELECT 
    `products`.`supplier_catalog_number`, 
    `prices`.`price`, 
    ROW_NUMBER() OVER (PARTITION BY `products`.`supplier_catalog_number`) - 1 `price_index` 
FROM 
    `products` 
    INNER JOIN `prices` ON `prices`.`product_id` = `products`.`id` 
ORDER BY 
    `products`.`supplier_catalog_number`, 
    `price_index` 
LIMIT 10; 

参见db<>fiddle。

一种方式来实现你所需要的（MySQL的）是执行下面的查询，但是，它不是实现它的唯一或有效途径：

mysql> SELECT VERSION(); 
+-----------+ 
| VERSION() | 
+-----------+ 
| 5.7.19 | 
+-----------+ 
1 row in set (0.00 sec) 

mysql> DROP TABLE IF EXISTS `prices`, `products`; 
Query OK, 0 rows affected (0.00 sec) 

mysql> CREATE TABLE IF NOT EXISTS `products` (
    -> `id` BIGINT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY, 
    -> `supplier_catalog_number` VARCHAR(12) NOT NULL 
    ->); 
Query OK, 0 rows affected (0.00 sec) 

mysql> CREATE TABLE IF NOT EXISTS `prices` (
    -> `id` BIGINT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY, 
    -> `price` DECIMAL(9, 4) NOT NULL, 
    -> `product_id` BIGINT UNSIGNED NOT NULL, 
    -> FOREIGN KEY (`product_id`) 
    ->  REFERENCES `products`(`id`) 
    ->); 
Query OK, 0 rows affected (0.00 sec) 

mysql> INSERT INTO `products` 
    -> (`supplier_catalog_number`) 
    -> VALUES 
    -> ('00000001600L'), 
    -> ('0023-200'), 
    -> ('0023-300'), 
    -> ('0023-301'); 
Query OK, 4 rows affected (0.00 sec) 
Records: 4 Duplicates: 0 Warnings: 0 

mysql> INSERT INTO `prices` 
    -> (`price`, `product_id`) 
    -> VALUES 
    -> (287.0000, 1), (243.9500, 1), 
    -> (710.0000, 2), (603.5000, 2), 
    -> (232.0000, 3), (185.6000, 3), 
    -> (289.0000, 4), (231.2000, 4), 
    -> (109.0000, 4), (92.6500, 4); 
Query OK, 10 rows affected (0.00 sec) 
Records: 10 Duplicates: 0 Warnings: 0 

mysql> SELECT 
    -> `der`.`supplier_catalog_number`, 
    -> `der`.`price`, 
    -> `der`.`price_index` 
    -> FROM (
    -> SELECT 
    ->  `products`.`supplier_catalog_number`, 
    ->  `prices`.`price`, 
    ->  (SELECT @`index` := IF(@`id` = `products`.`id`, @`index` + 1, 0)) `price_index`, 
    ->  (SELECT @`id` := `products`.`id`) 
    -> FROM 
    ->  (SELECT @`id` := 0, @`index` := 0) `init`, 
    ->  `products` 
    ->  INNER JOIN `prices` ON `prices`.`product_id` = `products`.`id` 
    -> ORDER BY 
    ->  `products`.`id`, 
    ->  `prices`.`price` 
    -> LIMIT 10 
    ->) `der` 
    -> ORDER BY 
    -> `der`.`supplier_catalog_number`, 
    -> `der`.`price_index`; 
+-------------------------+----------+-------------+ 
| supplier_catalog_number | price | price_index | 
+-------------------------+----------+-------------+ 
| 00000001600L   | 287.0000 |   0 | 
| 00000001600L   | 243.9500 |   1 | 
| 0023-200    | 710.0000 |   0 | 
| 0023-200    | 603.5000 |   1 | 
| 0023-300    | 232.0000 |   0 | 
| 0023-300    | 185.6000 |   1 | 
| 0023-301    | 289.0000 |   0 | 
| 0023-301    | 231.2000 |   1 | 
| 0023-301    | 109.0000 |   2 | 
| 0023-301    | 92.6500 |   3 | 
+-------------------------+----------+-------------+ 
10 rows in set (0.00 sec) 

见db-fiddle。