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Can GROUP BY return 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.
How do I eliminate duplicates in GROUP BY?
The group by clause can also be used to remove duplicates. The go to solution for removing duplicate rows from your result sets is to include the distinct keyword in your select statement. It tells the query engine to remove duplicates to produce a result set in which every row is unique.
Does GROUP BY count duplicates?
GROUP BY only treats two rows as duplicates if all the column values in both the rows are the same. If even a single column value in either of the row is non-matching, they are treated as unique.
How to eliminate duplicate values in aggregate function with distinct?
Finds the sum of all numerical values in the specified column for the rows in the group. DISTINCT in the SELECT clause and DISTINCT in an aggregate function do not return the same result. Including a non-DISTINCT aggregate function and a DISTINCT aggregate function in the same SELECT clause can produce misleading results.
How to use group by with distinct aggregates?
No need for distinct. In fact, we can even use a regular COUNT (*) expression to get the total number of orders per customer! So, we can simply add “GROUP BY Customer” to the previous SQL, calculate what we need with aggregate functions, and remove any columns (like OrderID) that we will not be summarizing.
How is aggregate transformation used to remove duplicate entries?
Removing duplicate rows A common use of the aggregate transformation is removing or identifying duplicate entries in source data. This process is known as deduplication. Based upon a set of group by keys, use a heuristic of your choosing to determine which duplicate row to keep.
When to use group by to remove duplicates?
GROUP BY does not “remove duplicates”. GROUP BY allows for aggregation. If all you want is to combine duplicated rows, use SELECT DISTINCT. If you need to combine rows that are duplicate in some columns, use GROUP BY but you need to to specify what to do with the other columns.