[英]SQL Query to get column values that correspond with MAX value of another column?
Ok, this is my query:好的,这是我的查询:
SELECT
video_category,
video_url,
video_date,
video_title,
short_description,
MAX(video_id)
FROM
videos
GROUP BY
video_category
When it pulls the data, I get the correct row for the video_id, but it pulls the first row for each category for the others.当它提取数据时,我得到了 video_id 的正确行,但它为其他类别提取了每个类别的第一行。 So when I get the max result for the video_id of category 1, I get the max ID, but the first row in the table for the url, date, title, and description.
因此,当我获得类别 1 的 video_id 的最大结果时,我获得了最大 ID,但获得了表中 url、日期、标题和描述的第一行。
How can I have it pull the other columns that correspond with the max ID result?我怎样才能让它拉出与最大 ID 结果相对应的其他列?
Edit: Fixed.编辑:固定。
SELECT
*
FROM
videos
WHERE
video_id IN
(
SELECT
DISTINCT
MAX(video_id)
FROM
videos
GROUP BY
video_category
)
ORDER BY
video_category ASC
I would try something like this:我会尝试这样的事情:
SELECT
s.video_id
,s.video_category
,s.video_url
,s.video_date
,s.video_title
,short_description
FROM videos s
JOIN (SELECT MAX(video_id) AS id FROM videos GROUP BY video_category) max
ON s.video_id = max.id
which is quite faster that your own solution这比您自己的解决方案要快得多
I recently released a new technique to handle this type of problem in MySQL.我最近发布了一种新技术来处理 MySQL 中的此类问题。
SCALAR-AGGREGATE REDUCTION标量减少
Scalar-Aggregate Reduction is by far the highest-performance approach and simplest method (in DB engine terms) for accomplishing this, because it requires no joins, no subqueries, and no CTE. Scalar-Aggregate Reduction 是迄今为止实现这一目标的最高性能方法和最简单的方法(用数据库引擎术语来说),因为它不需要连接、子查询和 CTE。
For your query, it would look something like this:对于您的查询,它看起来像这样:
SELECT
video_category,
MAX(video_id) AS video_id,
SUBSTRING(MAX(CONCAT(LPAD(video_id, 11, '0'), video_url)), 12) AS video_url,
SUBSTRING(MAX(CONCAT(LPAD(video_id, 11, '0'), video_date)), 12) AS video_date,
SUBSTRING(MAX(CONCAT(LPAD(video_id, 11, '0'), video_title)), 12) AS video_title,
SUBSTRING(MAX(CONCAT(LPAD(video_id, 11, '0'), short_description)), 12) AS short_description
FROM
videos
GROUP BY
video_category
The combination of scalar and aggregate functions does the following:标量函数和聚合函数的组合执行以下操作:
If you want to retrieve values in types other than CHAR, you may need to performa an additional CAST on the output, eg if you want video_date
to be a DATETIME:如果您想检索非 CHAR 类型的值,您可能需要对输出执行额外的 CAST,例如,如果您希望
video_date
为 DATETIME:
CAST(SUBSTRING(MAX(CONCAT(LPAD(video_id, 11, '0'), video_date)), 12) AS DATETIME)
Another benefit of this method over the self-joining method is that you can combine other aggregate data (not just latest values), or even combine first AND last item in the same query, eg与自联接方法相比,此方法的另一个好处是您可以组合其他聚合数据(不仅仅是最新值),甚至可以组合同一查询中的第一个和最后一个项目,例如
SELECT
-- Overall totals
video_category,
COUNT(1) AS videos_in_category,
DATEDIFF(MAX(video_date), MIN(video_date)) AS timespan,
-- Last video details
MAX(video_id) AS last_video_id,
SUBSTRING(MAX(CONCAT(LPAD(video_id, 11, '0'), video_url)), 12) AS last_video_url,
...
-- First video details
MIN(video_id) AS first_video_id,
SUBSTRING(MIN(CONCAT(LPAD(video_id, 11, '0'), video_url)), 12) AS first_video_url,
...
-- And so on
For further details explaining the benefits of this method vs other older methods, my full blog post is here: https://www.stevenmoseley.com/blog/tech/high-performance-sql-correlated-scalar-aggregate-reduction-queries有关解释此方法与其他旧方法的优点的更多详细信息,我的完整博客文章在这里: https : //www.stevenmoseley.com/blog/tech/high-performance-sql-correlated-scalar-aggregate-reduction-queries
Here is a more general solution (handles duplicates)这是一个更通用的解决方案(处理重复项)
CREATE TABLE test(
i INTEGER,
c INTEGER,
v INTEGER
);
insert into test(i, c, v)
values
(3, 1, 1),
(3, 2, 2),
(3, 3, 3),
(4, 2, 4),
(4, 3, 5),
(4, 4, 6),
(5, 3, 7),
(5, 4, 8),
(5, 5, 9),
(6, 4, 10),
(6, 5, 11),
(6, 6, 12);
SELECT t.c, t.v
FROM test t
JOIN (SELECT test.c, max(i) as mi FROM test GROUP BY c) j ON
t.i = j.mi AND
t.c = j.c
ORDER BY c;
SELECT video_category,video_url,video_date,video_title,short_description,video_id FROM videos t1 where video_id in (SELECT max(video_id) FROM videos t2 WHERE t1.video_category=t2.video_category );从视频 t1 中选择 video_category,video_url,video_date,video_title,short_description,video_id 其中 video_id 在 (SELECT max(video_id) FROM 视频 t2 WHERE t1.video_category=t2.video_category );
Please provide your input and output records so that it can be understood properly and tested.请提供您的输入和输出记录,以便正确理解和测试。
A slightly more "rustic" solution, but should do the job just the same:一个稍微“质朴”的解决方案,但应该做同样的工作:
SELECT
video_category,
video_url,
video_date,
video_title,
short_description,
video_id
FROM
videos
ORDER BY video_id DESC
LIMIT 1;
In other words, just produce a table with all of the columns that you want, sort it so that your maximum value is at the top, and chop it off so you only return one row.换句话说,只需生成一个包含您想要的所有列的表,对其进行排序,使最大值位于顶部,然后将其切掉,以便只返回一行。
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