For this example, we will use the following table with duplicate PK values. In this table the primary key is the two columns (col1, col2). We cannot create a unique index or PRIMARY KEY constraint since two rows have duplicate PKs. This procedure illustrates how to identify and remove the duplicates. Oracle database concepts, oracle tables, oracle date time functions, oracle views, oracle packages,oracle procedures,oracle functions, oracle pl/sql anonymous blocks, oracle dml operations, oracle ddl operations,oracle triggers,oracle objects,oracle user privileges, oracle table constraints, oracle materialized views, oracle queries, oracle sub queries, oracle correlated queries, oracle joins.
Summary: in this tutorial, you will learn how to find duplicate records in the Oracle Database.
Let’s start by setting up a sample table for the demonstration.
Setting up a sample table
First, the following statement creates a new table named
fruits that consists of three columns: fruit id, fruit name, and color:
Second, insert some rows into the
Third, query data from the
As you can see from the picture above, the
fruits table has duplicate records with the same information repeated in both
Finding duplicate rows using the aggregate function
To find duplicate rows from the
fruits table, you first list the fruit name and color columns in both
GROUP BY clauses. Then you count the number of appearances each combination appears with the
COUNT(*) function as shown below:
The query returned a single row for each combination of fruit name and color. It also included the rows without duplicates.
To return just the duplicate rows whose
COUNT(*) is greater than one, you add a
HAVING clause as follows:
So now we have duplicated record. It shows one row for each copy.
If you want to return all the rows, you need to query the table again as shown below:
Now, we have all duplicate rows displayed in the result set.
Finding duplicate records using analytic function
See the following query:
In this query, we added an
OVER() clause after the
COUNT(*) and placed a list of columns, which we checked for duplicate values, after a partition by clause. The partition by clause split rows into groups.
Different from using the
GROUP BY above, the analytic function preserves the result set, therefore, you still can see all the rows in the table once.
Because you can use the analytic function in the
HAVING clause, you need to use the
Or you need to use an inline view:
Now, you should know how to how to find duplicate records in Oracle Database. It’s time to clean up your data by removing the duplicate records.
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