What is the difference between distinct and GROUP BY?

What is the difference between distinct and GROUP BY?

When and where to use GROUP BY and DISTINCT. DISTINCT is used to filter unique records out of the records that satisfy the query criteria. The “GROUP BY” clause is used when you need to group the data and it should be used to apply aggregate operators to each group.

Is GROUP BY or distinct better?

DISTINCT is used to filter unique records out of all records in the table. It removes the duplicate rows. SELECT DISTINCT will always be the same, or faster than a GROUP BY.

Does distinct affect performance?

Yes, the application needs to compare every record to the “distinct” records cache as it goes. You can improve performance by using an index, particularly on the numeric and date fields.

Is GROUP BY like distinct?

The group by gives the same result as of distinct when no aggregate function is present. The SQL Server query optimizer produces the same plan for both the queries as shown below. Thus, to conclude there is a functional difference as mentioned above even if the group by produces same result as of distinct.

Is GROUP BY or distinct faster?

The GROUP BY clause is faster than the SELECT DISTINCT clause (at least in these tests) because it does not require writing to a temporary file on disk.

Why GROUP BY is faster than distinct?

DISTINCT would usually be faster than GROUP BY if a) there’s no index on that column and b) you are not ordering as well since GROUP BY does both filtering and ordering.

Which is faster distinct or GROUP BY in Oracle?

Looking at your query above, I am guessing that the reason why group by is faster (without seeing the query), is that the location of the group by reduces the number of records that end up being returned. Whereas distinct is blowing out the result set and doing row by row comparisons.

What is difference between distinct and unique?

The main difference between Unique and Distinct in SQL is that Unique helps to ensure that all the values in a column are different while Distinct helps to remove all the duplicate records when retrieving the records from a table.

Is distinct an expensive operation?

In a table with million records, SQL Count Distinct might cause performance issues because a distinct count operator is a costly operator in the actual execution plan.

Is distinct faster than Row_number?

In my experience, an aggregate (DISTINCT or GROUP BY) can be quicker then a ROW_NUMBER() approach. Saying that, ROW_NUMBER is better with SQL Server 2008 than SQL Server 2005. However, you’ll have to try for your situation.

What is difference between distinct?

Distinct and different are similar words, but they are not always used the same way. Distinct means “different in a way that you can see, hear, smell, feel, etc.” or “noticeably different.” Different means “not of the same kind” or “partly or totally unlike.”

What is a distinct value?

So, what are distinct and what are unique values in Excel? Unique values are the items that appear in a dataset only once. Distinct values are all different items in a list, i.e. unique values and 1st occurrences of duplicate values.