As my example illustrates, GROUP BY can be faster than DISTINCT if you are ordering as well and if you are doing JOINs, selecting a lot of columns, etc If you use both DISTINCT and GROUP BY the optimiser seems to ignore the DISTINCT And most importantly, always try both to see which is faster in your use case! Does that sound right?
Which is faster-group by or distinct?
Feb 24, 2009 · If one of them is faster, it's going to be DISTINCT. This is because, although the two are the same, a query optimizer would have to catch the fact that your GROUP BY is not taking advantage of any group members, just their keys. DISTINCT makes this explicit, so you can get away with a slightly dumber optimizer. When in doubt, test!
Which is faster group by OR SELECT query?
Jan 26, 2017 · One of the items I always mention in that session is that I generally prefer GROUP BY over DISTINCT when eliminating duplicates. While DISTINCT better explains intent, and GROUP BY is only required when aggregations are present, they are interchangeable in many cases. Let's start with something simple using Wide World Importers. These two queries …
What is the difference between group by and distinct?
Jun 29, 2020 · Thereof, is group by faster than distinct SQL Server? GROUP BY and DISTINCT both generate the same query execution plan when no aggregates are used, so there is no appreciable difference in performance in this situation. GROUP BY becomes important when aggregates are used. DISTINCT is just for filtering out duplicate records from query result sets.
What is the difference between group by and distinct thumbsuck?
Click to see full answer. Also to know is, which one is faster distinct or group by? SELECT DISTINCT will always be the same, or faster, than a GROUP BY. On some systems (i.e. Oracle), it might be optimized to be the same as DISTINCT for most queries. On others (such as SQL Server), it can be considerably faster.
Is it better to use GROUP BY or distinct?
In MySQL, DISTINCT seems a bit faster than GROUP BY if theField is not indexed. DISTINCT only eliminate duplicate rows but GROUP BY seems to sort them in addition.Dec 17, 2008
Which is faster distinct or GROUP BY in hive?
@Ravi teja Based on my encounters, group by will be faster than distinct. Groupby is something similar to segregating the key, values which MR is capable of handling it with ease.Dec 13, 2017
Which is faster GROUP BY or distinct in Oracle?
GROUP BY should be used to apply aggregate operators to each group. If all you need is to remove duplicates then use DISTINCT. If you are using sub-queries execution plan for that query varies so in that case you need to check the execution plan before making decision of which is faster.
Why is GROUP BY better than distinct SQL?
GROUP BY lets you use aggregate functions, like AVG , MAX , MIN , SUM , and COUNT . On the other hand DISTINCT just removes duplicates. This will give you one row per department, containing the department name and the sum of all of the amount values in all rows for that department.
Is GROUP BY faster than distinct Postgres?
From experiments, I founded that the GROUP BY is 10+ times faster than DISTINCT.Aug 7, 2015
What is faster distinct or GROUP BY Postgres?
The DISTINCT variation took 4X as long, used 4X the CPU, and almost 6X the reads when compared to the GROUP BY variation. (Remember, these queries return the exact same results.)Jan 26, 2017
Which is faster partition by or GROUP BY?
The IO for the PARTITION BY is now much less than for the GROUP BY, but the CPU for the PARTITION BY is still much higher. Even when there is lots of memory, PARTITION BY – and many analytical functions – are very CPU intensive.Jun 5, 2009
Why distinct is bad in SQL?
This is why I get nervous about use of " distinct " - the spraddr table may include additional columns which you should use to filter out data, and " distinct " may be hiding that. Also, you may be generating a massive result set which needs to be filtered by the "distinct" clause, which can cause performance issues.Nov 11, 2015
Does distinct reduce performance?
It kills performance (unless query planner can determine it is superfluous; I don't know how well oracle does that). You should know from the cardinality of your joins, uniqueness of columns, conditions that you apply and the results that you expect if you need it or not.
Should I use distinct?
The distinct keyword is used in conjunction with select keyword. It is helpful when there is a need of avoiding duplicate values present in any specific columns/table. When we use distinct keyword only the unique values are fetched.Sep 11, 2020
What can we use instead of GROUP BY?
SQL Sub-query as a GROUP BY and HAVING Alternative You can use a sub-query to remove the GROUP BY from the query which is using SUM aggregate function. There are many types of subqueries in Hive, but, you can use correlated subquery to calculate sum part.Jan 24, 2020
Does distinct affect performance?
Yes, the application needs to compare every record to the "distinct" records cache as it goes. You can improve performance by using an index, particularly on the numeric and date fields.