SQL Query to get column values that correspond with MAX value of another column?

Question

Ok, this is my query:

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. 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.

How can I have it pull the other columns that correspond with the max ID result?

Edit: Fixed.

SELECT     * FROM     videos WHERE     video_id IN     (         SELECT             DISTINCT             MAX(video_id)         FROM             videos         GROUP BY             video_category     )  ORDER BY     video_category ASC 

Answer 1

I would try something like this:

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

Answer 2

I recently released a new technique to handle this type of problem in MySQL.

SCALAR-AGGREGATE REDUCTION

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.

For your query, it would look something like this:

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:

1. LPADs the intra-aggregate correlated identifier to allow proper string comparison (e.g. "0009" and "0025" will be properly ranked). I'm LPADDING to 11 characters here assuming an INT primary key. If you use a BIGINT, you will want to increase this to support your table's ordinality. If you're comparing on a DATETIME field (fixed length), no padding is necessary.
2. CONCATs the padded identifier with the output column (so you get "00000000009myvalue" vs "0000000025othervalue")
3. MAX the aggregate set, which will yield "00000000025othervalue" as the winner.
4. SUBSTRING the result, which will truncate the compared identifier portion, leaving only the value.

If you want to retrieve values in types other than CHAR, you may need to performa an additional CAST on the output, e.g. if you want video_date to be a 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, e.g.

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