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Why does MySQL not group by DESC order?
The reason why you were getting the unusual result is because MySQL uses an extension to GROUP BY which allows items in a select list to be nonaggregated and not included in the GROUP BY clause. This however can lead to unexpected results because MySQL can choose the values that are returned.
How to combine group by, order by and having in MySQL?
Most RDBMS will not even allow you to do this because of the issues it creates, but MySQL is the exception. Steps for Using Group by,Having By and Order by… Select Attitude ,count (*) from Person group by person HAving PersonAttitude=’cool and friendly’ Order by PersonName.
When to use group by or order by in SQL?
The GROUP BY clause groups the rows, but it does not necessarily sort the results in any particular order. To change the order, use the ORDER BY clause, which follows the GROUP BY clause. The columns used in the ORDER BY clause must appear in the SELECT list, which is unlike the normal use of ORDER BY.
How is data sorted in a group in MySQL?
When you are doing a GROUP BY by default it sorts data by the grouping field (post_author, in our case; post_status, post_type are required by the WHERE clause) and if there is a matching index, it takes data for each first record in ascending order.
How to group by DESC order by id?
Query SELECT max (id) as id, asker FROM questions GROUP BY asker ORDER BY id DESC returns expected: Query SELECT max (id) as id, asker, other FROM questions GROUP BY asker ORDER BY id DESC returns unexpected:
When to use Max and group by in MySQL?
The records need to be grouped using GROUP BY and MAX () to get the maximum ID for every asker. The others are correct about using MAX (ID) to get the results you want. If you’re wondering why your query doesn’t work, it’s because ORDER BY happens after the GROUP BY.
How to use the group by clause in MySQL?
(See MySQL Extensions to GROUP BY) MySQL extends the use of GROUP BY so that the select list can refer to nonaggregated columns not named in the GROUP BY clause. You can use this feature to get better performance by avoiding unnecessary column sorting and grouping.
Do you have to group by column in MySQL?
MySQL does not force you to GROUP BY every column that you include in the SELECT list. As a result, if you only GROUP BY one column but return 10 columns in total, there is no guarantee that the other column values which belong to the post_author that is returned.
How does MySQL process order by and limit in a query?
If you need to keep the result in ascending order, and still only want the 10 newest articles you can ask mysql to sort your result two times. This query below will sort the result descending and limit the result to 10 (that is the query inside the parenthesis).
Why does group by trick work in MySQL?
GROUP BY trick has been optimized away shows a situation in which the same query returns different results between MySql and MariaDB, probably because of a different optimization engine. So, if this trick works, it’s just a matter of luck.