INSERT INTO Users (FirstName, LastName) VALUES (N'Elvis',N'Presley') INSERT INTO Users (FirstName, LastName) VALUES (N'Eralper',N'Yilmaz') Table to distinguish identical rows in the table. And the third method is adding an identity column to the Versions of SQL Server, then you should prefer choosing the second method and So if you are writing your sql codes also for next Not affect DELETE, INSERT, and UPDATE statements in the next release of SQL ![]() But if you open the SQL ServerĢ005 Books Online (BOL) you will see a note indicating that SET ROWCOUNT will One method is using the SET ROWCOUNT t-sql command.Īnd the second method uses the TOP tsql command. There are three methods that we can get use of them in order toĭelete dublicates in a table. In a way using identity columns will also provide a uniqueness among the rows ofĪ table as well as in the identity column values.īut now we will deal with a situation where we can not avoid dublicate records in a table and try to remove or delete the dublicate rows from the database table. Identity columns areĬolumns whose numeric values are generated automatically in a sequential way. Values so each row in the table has also no dublicates. Unique indexes guarantees that columns within the index has no dublicate Occur on any table if the table does not have a unique index or an identityĬolumn. So you can not distinguish one row from the other. This is a real problem if the records are identical even for values in eachĬolumn. It is a very common situation that you may find yourselfĪgainst a problem dealing with deletion of dublicate records in a database table. Now you should know how to delete duplicate records in the Oracle Database.How to delete duplicate records or rows among identical rows in a table where no primary key exists The following query verifies the delete operation: SELECTįruits Code language: SQL (Structured Query Language) ( sql ) ) Code language: SQL (Structured Query Language) ( sql ) Because the rowid is unique to each row, you can use it to remove the duplicates as shown below: DELETE FROM In this case, you can use the rowid which is a physical locator that specifies where on storage Oracle stores the row. In the fruits table, the values in all columns fruit_id, fruit_name, and color have copies. INSERT INTO fruits(fruit_id,fruit_name,color) VALUES( '4,Banana', 'Green') INSERT INTO fruits(fruit_id,fruit_name,color) VALUES( 3, 'Banana', 'Yellow') INSERT INTO fruits(fruit_id,fruit_name,color) VALUES( 2, 'Orange', 'Orange') INSERT INTO fruits(fruit_id,fruit_name,color) VALUES( 1, 'Apple', 'Red') Let’s drop and create the fruits table with a new structure and data as follows: DROP TABLE fruits If all values in all columns can have copies, then you cannot use the fruit_id column anymore. This method above works if you have a column that is not part of the group for evaluating duplicates. Likewise, if you want to keep the row with the lowest ID, you use the MIN() function instead of the MAX() function: DELETE FROM Three rows were deleted which is what we expected: SELECT You use the following DELETE statement with a subquery to delete rows whose values are in the fruit_id column are not the highest ones. ![]() The following query returns the last entry for each combination of fruit_name and color: SELECT MAX(fruit_id) Suppose you want to keep the row with the highest fruit_id and delete all other copies. query data from the fruit table SELECT * FROM fruits Ĭode language: SQL (Structured Query Language) ( sql ) INSERT INTO fruits(fruit_name,color) VALUES( 'Banana', 'Green') INSERT INTO fruits(fruit_name,color) VALUES( 'Banana', 'Yellow') INSERT INTO fruits(fruit_name,color) VALUES( 'Orange', 'Orange') INSERT INTO fruits(fruit_name,color) VALUES( 'Apple', 'Red') insert sample rows INSERT INTO fruits(fruit_name,color) VALUES( 'Apple', 'Red') In this case, you need a column in the table like id column that is not the part of the group used to evaluate duplicate.Ĭonsider the following fruits table: - create fruit table CREATE TABLE fruits (įruit_id NUMBER generated BY DEFAULT AS IDENTITY, For example, you may want to preserve the newest or oldest row. It is better to construct a single statement that removes all unwanted copies in one go.īefore removing the duplicate records, you must decide which instances you want to keep. However, it is time-consuming to do it manually if the table has a large number of duplicate records. If a table has a few duplicate rows, you could do this manually one by one by using a simple DELETE statement. Once you’ve found the duplicate records in a table, you often want to delete the unwanted copies to keep your data clean. Summary: in this tutorial, you will learn step by step how to delete duplicate records in Oracle Database using the DELETE statement with a subquery.
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