Distinct is used to find unique/distinct records where as a group by is used to group a selected set of rows into summary rows by one or more columns or an expression. ... The group by gives the same result as of distinct when no aggregate function is present.
Is it better to use distinct or GROUP BY?
In MySQL, DISTINCT seems a bit faster than GROUP BY if theField is not indexed. DISTINCT only eliminate duplicate rows but GROUP BY seems to sort them in addition.
What is the difference between GROUP BY and distinct in MySQL?
3 Answers. Well group by and distinct has its own use . Distinct is used to filter unique records out of the records that satisfy the query criteria. Group by clause is used to group the data upon which the aggregate functions are fired and the output is returned based on the columns in the group by clause.
Can I use distinct and GROUP BY together?
Make a decision of which one is better in your query by checking the execution plans and determine the relative efficiency of queries that generate the same result set. Well, GROUP BY and DISTINCT have their own use . GROUP BY cannot replace DISTINCT in some situations and DISTINCT cannot take place of GROUP BY.
Which is quicker distinct or GROUP BY?
DISTINCT creates a temporary table and uses it for storing duplicates. GROUP BY does the same, but sortes the distinct results afterwards. is faster, if you don’t have an index on profession .
Does GROUP BY remove duplicates?
5 Answers. GROUP BY does not “remove duplicates” . GROUP BY allows for aggregation. If all you want is to combine duplicated rows, use SELECT DISTINCT.
Does GROUP BY makes query slow?
The query is executed over 11400000 rows and runs very slow. It takes over 3 minutes to execute. If I remove the group-by part, this runs below 1 second.
What is GROUP BY in mysql?
The MYSQL GROUP BY Clause is used to collect data from multiple records and group the result by one or more column . It is generally used in a SELECT statement. You can also use some aggregate functions like COUNT, SUM, MIN, MAX, AVG etc.
Which is better distinct or GROUP BY in Oracle?
While DISTINCT better explains intent , and GROUP BY is only required when aggregations are present, they are interchangeable in many cases. ... GROUP BY can (again, in some cases) filter out the duplicate rows before performing any of that work.
Can you GROUP BY multiple columns in SQL?
SQL GROUP BY multiple columns is the technique using which we can retrieve the summarized result set from the database using the SQL query that involves grouping of column values done by considering more than one column as grouping criteria.
What is difference between distinct and unique?
The main difference between unique and distinct is that UNIQUE is a constraint that is used on the input of data and ensures data integrity. While DISTINCT keyword is used when we want to query our results or in other words, output the data.
Does GROUP BY return unique values?
Columns that are listed after GROUP BY are certain to reflect only one distinct value within a group, and that value can be returned. However, a column not listed after GROUP BY might contain different values in the rows that are contained in the group.
What can I use instead of GROUP BY?
The important thing is that i can not use group by. The only things I can use is: select , from , where , union , intersect , minus , distinct , count , and , or , as , between .
Is GROUP BY faster than distinct postgresql?
From experiments, I founded that the GROUP BY is 10+ times faster than DISTINCT . They are different. So what I learned is: GROUP-BY is anyway not worse than DISTINCT, and it is better sometimes.
Does distinct reduce performance?
Yes , as using DISTINCT will (sometimes according to a comment) cause results to be ordered. Sorting hundreds of records takes time. Try GROUP BY all your columns, it can sometimes lead the query optimiser to choose a more efficient algorithm (at least with Oracle I noticed significant performance gain).
How can we make a group more efficient?
The Bottom Line: Optimal GROUP BY Clauses
GROUP BY performs better if you keep the number of grouping columns small. Avoid grouping redundant columns by using set functions. When you’re grouping joined tables, reduce before you expand. You can make a join happen late by replacing it with a set operator.
