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