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Is distinct on faster than distinct?
DISTINCT is used to filter unique records out of all records in the table. It removes the duplicate rows. SELECT DISTINCT will always be the same, or faster than a GROUP BY.
Is distinct fast?
DISTINCT is much faster with large amount data. I tested this, and found that on an indexed column, mysql, group by was about 6x slower than distinct with a fairly complicated query. Just adding this as a datapoint.
Is Count distinct slow?
It’s slow because the database is iterating over all the logs and all the dashboards, then joining them, then sorting them, all before getting down to real work of grouping and aggregating.
How to speed up SELECT DISTINCT queries in pubs?
Take this simple PUBS database query as an example: In a simple select from one table (like the one above) this is the easiest and quickest way of doing things. However, with a more complex query you can think about re-coding it to gain a performance advantage. Take this example query, which only returns authors that have a book already published.
Why is my SELECT DISTINCT query so slow?
Pretending that I’m 100% certain the DISTINCT portion of the query is the reason it runs slowly, I’ve omitted the rest of the query to avoid confusion, since it is the distinct portion’s slowness that I’m primarily concerned with (distinct is always a source of slowness). The table in question has 2.5 million rows of data.
How to speed up SELECT DISTINCT query in Postgres?
If you put an index on the column (s) selected by the query, the database may be able to read them out in index order and save the sort step. A lot will depend on the details of the query and the tables involved– your saying you “know the problem is with the DISTINCT” really limits the scope of available answers.
How are distinct queries used in Microsoft Excel?
On the other hand, the DISTINCT query returns one copy of the author’s name for each book the author has worked on, and the list of authors generated subsequently needs to be examined for duplicates to satisfy the DISTINCT clause. You can examine the execution plan for each query to see where the performance improvements come from.