At times, when using DISTINCT, you run out of spool space on an AMP. Performance of GROUP BY vs. PARTITION BY. Archived Forums > Transact-SQL. After looking at someone else's query I noticed they were doing a group by to obtain the unique list. Is there any dissadvantage of using "group by" to obtain a unique list? Groupby is something similar to segregating the key, values which MR is capable of handling it with ease. The reason is that redistribution takes place immediately, and skewing could cause AMPs to … I would say better to go with group … DISTINCT. Do not use the DISTINCT phrase, unless the number of distinct values is high." I am trying to get a distinct set of rows from 2 tables. You can examine the execution plan for each query to see where the performance improvements come from. How does SQL2k handle the distinct keyword? 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 run out of space. Here is my result. Does it … But hey, repetition is a good thing… I hope? In fact, if you… 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, … Recently, Aaron Bertrand (b/t) posted Performance Surprises and Assumptions : GROUP BY vs. In short, DISTINCT vs. GROUP BY in Teradata means: GROUP BY -> for many duplicates DISTINCT -> no or a few duplicates only . 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. 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. 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 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. ... - 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 … He discusses the fact that GROUP BY will, in fact, under certain circumstances, produce a faster query plan. To test distinct vs group by performance in SQL Query I wrote essentially same query using two different ways. @Ravi teja Based on my encounters, group by will be faster than distinct. I highly recommend taking the time to read it. 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. In it he says he prefers GROUP BY over DISTINCT. I compared execution plan generated by SQL Server. 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