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In performance wise distinct is good or group by is good?
eg:select name from emp group by name;
select distinct name from emp;
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Answer Posted / madhu
This question is asked many times to me. What is difference
between DISTINCT and GROUP BY?
A DISTINCT and GROUP BY usually generate the same query
plan, so performance should be the same across both query
constructs. 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.
Example of DISTINCT:
SELECT DISTINCT Employee, Rank
FROM Employees
Example of GROUP BY:
SELECT Employee, Rank
FROM Employees
GROUP BY Employee, Rank
| Is This Answer Correct ? | 14 Yes | 3 No |
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