给定以下查询
SET @num :=0, @current_shop_id := NULL, @current_product_id := NULL;
SELECT * FROM (
SELECT products.shop_id, products.product_id, @num := IF(@current_shop_id=shops.shop_id, IF(@current_product_id=products.product_id,@num,@num+1),0) AS row_number, @current_shop_id := shops.shop_id AS shop_dummy, @current_product_id := products.product_id AS product_dummy
FROM
favorites fav1 INNER JOIN
products ON
fav1.product_id=products.product_id AND
fav1.current=1 AND
fav1.closeted=1 AND
fav1.user_id=30 INNER JOIN
shops ON
shops.shop_id = products.shop_id
ORDER BY shops.shop ASC, products.product_id DESC
) AS rowed_results WHERE rowed_results.row_number>=0 AND rowed_results.row_number<(20) AND shop_id=130
我期待表单的 row_number 值
+---------+------------+------------+------------+---------------+
| shop_id | product_id | row_number | shop_dummy | product_dummy |
+---------+------------+------------+------------+---------------+
| 130 | 1153746 | 0 | 130 | 1153746 |
| 130 | 1153736 | 1 | 130 | 1153736 |
| 130 | 1139944 | 2 | 130 | 1139944 |
| 130 | 1098296 | 3 | 130 | 1098296 |
| 130 | 1017455 | 4 | 130 | 1017455 |
| 130 | 551953 | 5 | 130 | 551953 |
| 130 | 551914 | 6 | 130 | 551914 |
+---------+------------+------------+------------+---------------+
(即，与给定 shop_id 值关联的所有唯一 product_id 值都获得一个唯一的行号，从 0 开始)。相反，我得到了
+---------+------------+------------+------------+---------------+
| shop_id | product_id | row_number | shop_dummy | product_dummy |
+---------+------------+------------+------------+---------------+
| 130 | 1153746 | 1 | 130 | 1153746 |
| 130 | 1153736 | 0 | 130 | 1153736 |
| 130 | 1139944 | 0 | 130 | 1139944 |
| 130 | 1098296 | 0 | 130 | 1098296 |
| 130 | 1017455 | 0 | 130 | 1017455 |
| 130 | 551953 | 1 | 130 | 551953 |
| 130 | 551914 | 0 | 130 | 551914 |
+---------+------------+------------+------------+---------------+
我做错了什么？
编辑:
Michael Berkowski 的解决方案(使用三个查询，一个用于检索数据，一个用于添加行号，一个用于按行限制)有效(语法略有更改):
SET @num :=0, @current_shop_id := NULL, @current_product_id := NULL;
#limit by row
SELECT * FROM (
#add row
SELECT limit_query.*, @num := IF(@current_shop_id=shop_id, IF(@current_product_id=product_id,@num,@num+1),0) AS row_number, @current_shop_id := shop_id AS shop_dummy, @current_product_id := product_id AS product_dummy FROM (
#retrieve data
SELECT row_query.* FROM (
SELECT products.shop_id, products.product_id
FROM
favorites fav1 INNER JOIN
products ON
fav1.product_id=products.product_id AND
fav1.current=1 AND
fav1.closeted=1 AND
fav1.user_id=30 INNER JOIN
shops ON
shops.shop_id = products.shop_id
) AS row_query ORDER BY shop_id ASC, product_id DESC
) AS limit_query
) AS rowed_results WHERE rowed_results.row_number>=0 AND rowed_results.row_number<(20) AND shop_id=130;
纯粹出于教育兴趣，我想知道为什么不能同时添加行号和按行号限制，如以下(非功能性)示例
SET @num :=0, @current_shop_id := NULL, @current_product_id := NULL;
#limit by row
SELECT rowed_results.*, @num := IF(@current_shop_id=shop_id, IF(@current_product_id=product_id,@num,@num+1),0) AS row_number, @current_shop_id := shop_id AS shop_dummy, @current_product_id := product_id AS product_dummy FROM (
#retrieve data
SELECT row_query.* FROM (
SELECT products.shop_id, products.product_id
FROM
favorites fav1 INNER JOIN
products ON
fav1.product_id=products.product_id AND
fav1.current=1 AND
fav1.closeted=1 AND
fav1.user_id=30 INNER JOIN
shops ON
shops.shop_id = products.shop_id
) AS row_query ORDER BY shop_id ASC, product_id DESC
) AS rowed_results WHERE row_number>=0 AND row_number<(20) AND shop_id=130;
最佳答案
要使行递增，只需将 @num 计算移动到外部查询中即可。在这种情况下，不需要 @current_product_id，因为 @num 可以直接递增。
SET @num :=0, @current_shop_id := NULL, @current_product_id := NULL;
SELECT
*,
/* Perform the row increment in the outer query so it acts on the final rowset */
@num := @num+1 AS row_number
FROM (
SELECT products.shop_id, products.product_id, @current_shop_id := shops.shop_id AS shop_dummy, @current_product_id := products.product_id AS product_dummy
FROM
favorites fav1 INNER JOIN
products ON
fav1.product_id=products.product_id AND
fav1.current=1 AND
fav1.closeted=1 AND
fav1.user_id=30 INNER JOIN
shops ON
shops.shop_id = products.shop_id
ORDER BY shops.shop ASC, products.product_id DESC
) AS rowed_results
WHERE
rowed_results.row_number>=0
AND rowed_results.row_number<(20)
AND shop_id=130
关于mysql - 为什么这个 MySQL 查询会产生错误的行号？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/14664516/