Mysql distinct vs group by

For example: MAX, AVG etc. MySQL MySQLi Database. This can be applied on a si. Verwendest Du keine Aggregatsfuktionen und möchtest einfach nur eindampfen, dann schreibt man DISTINCT. If all you need is to remove duplicates then use DISTINCT.

Huge performance difference when using group by vs distinct. Ask Question Asked years, month ago. Active years, months ago. Viewed 100k times 71.

However, in more complex cases, DISTINCT can end up doing more work. Essentially, DISTINCT collects all of the rows, including any expressions that need to be evaluate and then tosses out duplicates. Both can be used to distinguish the values but if in performance point of view group by is better. When distinct keyword is used , internally it used sort operation which can be view in execution plan.

Well, not necessarily. There is no difference in your queries for Oracle versions up to 10. Still, performance should be similar. My query above will be superior in versions 10. Use it to remove duplicate records and it can be used with aggregate function as well.

And the Only difference between them is: Group By will sort the Data first, and then perform grouping. Theoretische hätte ich gedacht, dass DISTINCT schneller greift und daher kürzer läuft. Distinct keyword does not perform any sorting. Доброго времени суток! В связи с оптимизацией скриптов, посоветуйте, что.

In other words, it reduces the number of rows in the result set. GROUP BY clause is not sorted. DISTINCT dice: dejemos un registro de cada uno, tengo registro de pedro. SpringMVC框架上传表单时怎么将表单数据与实体对象绑定，然后在控制器中调用.

Explore SQL with Tom Coffing of Coffing Data Warehousing! Vorteil: einfach zu nutzen, z. While doing some performance turning on a procedure, I came across a case where not only does the performance vary between a statement using distinct vs. Abfragen (nested selects). If you could let me know what is vexing you, I can try to explain that part.

The summary can come out in any order.