Does it … To test distinct vs group by performance in SQL Query I wrote essentially same query using two different ways. After comparing on multiple machines with several tables, it seems using group by to obtain a distinct list is substantially faster than using select distinct. The reason is that redistribution takes place immediately, and skewing could cause AMPs to run out of space. How does SQL2k handle the distinct keyword? In fact, if you… Archived Forums > Transact-SQL. At times, when using DISTINCT, you run out of spool space on an AMP. Does SQL filter the duplicates on the fly? Select Distinct Brand From TABLE where price between 19 and 25. if I dont do distinct Then i will see GE twice..my table has around 30K Rows....so what is the best approach to go around this issue (best performance) ..I dont need Group by VS Distinct solution...I need to know best practice to avoid these issues. In it he says he prefers GROUP BY over DISTINCT. In short, DISTINCT vs. GROUP BY in Teradata means: GROUP BY -> for many duplicates DISTINCT -> no or a few duplicates only . He discusses the fact that GROUP BY will, in fact, under certain circumstances, produce a faster query plan. @Ravi teja Based on my encounters, group by will be faster than distinct. DISTINCT. ... - Group BY with hashout the keys and then apply distinct on it.. so If you have nested queries or Views then its a never ending story. SQL Server Performance Forum – Threads Archive Distinct vs. Group By I’ll bet your paycheck this thread has been posted before. I highly recommend taking the time to read it. Hi when i tried to find the answer fot this thread in one of the link i found a answer as "Group By Vs Distinct When there is a low number of distinct values, it is more efficient to use the GROUP BY phrase. I am trying to get a distinct set of rows from 2 tables. The reason is that redistribution takes place immediately, and skewing could cause AMPs to … 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. I would say better to go with group … But hey, repetition is a good thing… I hope? Performance of GROUP BY vs. PARTITION BY. In short, DISTINCT vs. GROUP BY in Teradata means: GROUP BY -> for many duplicates; DISTINCT -> no or a few duplicates only; At times, when using DISTINCT, you run out of spool space on an AMP. Recently, Aaron Bertrand (b/t) posted Performance Surprises and Assumptions : GROUP BY vs. After looking at someone else's query I noticed they were doing a group by to obtain the unique list. Do not use the DISTINCT phrase, unless the number of distinct values is high." I wrote a post recently about DISTINCT and GROUP BY.It was a comparison that showed that GROUP BY is generally a better option than DISTINCT. Looks like SQL Server was smart enough to detect that I am trying … You can examine the execution plan for each query to see where the performance improvements come from. Groupby is something similar to segregating the key, values which MR is capable of handling it with ease. Is there any dissadvantage of using "group by" to obtain a unique list? It's on a different site, but be sure to come back to sqlperformance.com right after... One of the query comparisons that I showed in that post was between a GROUP BY and DISTINCT for a sub-query, showing that the DISTINCT is a lot slower, … Here is my result. I compared execution plan generated by SQL Server. Same query using two different ways you can examine the execution plan for query... Plan for each query to see distinct vs group by performance the performance improvements come from Ravi Based! 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