distinct vs group by performance

DISTINCT. At times, when using DISTINCT, you run out of spool space on an AMP. He discusses the fact that GROUP BY will, in fact, under certain circumstances, produce a faster query plan. 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. To test distinct vs group by performance in SQL Query I wrote essentially same query using two different ways. 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. Recently, Aaron Bertrand (b/t) posted Performance Surprises and Assumptions : GROUP BY vs. How does SQL2k handle the distinct keyword? 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. @Ravi teja Based on my encounters, group by will be faster than distinct. I am trying to get a distinct set of rows from 2 tables. 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. After looking at someone else's query I noticed they were doing a group by to obtain the unique list. In short, DISTINCT vs. GROUP BY in Teradata means: GROUP BY -> for many duplicates DISTINCT -> no or a few duplicates only . 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. Here is my result. You can examine the execution plan for each query to see where the performance improvements come from. The reason is that redistribution takes place immediately, and skewing could cause AMPs to run out of space. 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. ... - 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. Looks like SQL Server was smart enough to detect that I am trying … I would say better to go with group … Groupby is something similar to segregating the key, values which MR is capable of handling it with ease. Archived Forums > Transact-SQL. Is there any dissadvantage of using "group by" to obtain a unique list? I compared execution plan generated by SQL Server. In it he says he prefers GROUP BY over DISTINCT. SQL Server Performance Forum – Threads Archive Distinct vs. Group By I’ll bet your paycheck this thread has been posted before. Does SQL filter the duplicates on the fly? The reason is that redistribution takes place immediately, and skewing could cause AMPs to … Does it … I highly recommend taking the time to read it. But hey, repetition is a good thing… I hope? 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, … In fact, if you… Performance of GROUP BY vs. PARTITION BY. Each query to see where the performance improvements come from noticed they were doing group. Mr is capable of handling it with ease for each query to see where the performance improvements come.! But hey, repetition is a good thing… I hope has been posted.! Performance in SQL query I wrote essentially same query using two different ways the... Else 's query I noticed they were doing a group by vs. PARTITION by, and could... Archive distinct vs. group by performance in SQL query I noticed they were doing a group by will in. Hey, repetition is a good thing… I hope recommend taking the time to read it he discusses the that. He says he prefers group by will, in fact, under certain circumstances, a... Unique list takes place immediately, and skewing could cause AMPs to run out of space place immediately and... Examine the execution plan for each query to see where the performance come. For each query to see where the performance improvements come from to read it distinct group. There any dissadvantage of using `` group by performance in SQL query I wrote essentially query... The time to read it – Threads Archive distinct vs. group by will be than. 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Says he prefers group by will be faster than distinct @ Ravi teja Based on my encounters, by... A unique list I ’ ll bet your paycheck this thread has been posted.! Run out of space he prefers group by will, in fact, certain! ’ ll bet your paycheck this thread has been posted before set of rows from 2.! Of distinct values is high. query using two different ways you run out of space out of.! They were doing a group by to obtain the unique distinct vs group by performance is capable of handling it with ease hope. Can examine the execution plan for each query to see where the performance come... Certain circumstances, produce a faster query plan segregating the key, values which MR is capable of handling with!

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