How to Delete Duplicates In Oracle?

To delete duplicates in Oracle, you can use the DELETE statement with a subquery that uses the ROWID pseudocolumn to identify the duplicate rows. You can use the following query:

DELETE FROM your_table WHERE ROWID NOT IN (SELECT MAX(ROWID) FROM your_table GROUP BY column1, column2, ...);

In this query, replace "your_table" with the name of your table and "column1, column2, ..." with the columns that determine duplicate rows. This query will keep only one instance of each duplicate row in the table.

How to delete duplicates in Oracle by creating a new table with unique records?

To delete duplicates in Oracle by creating a new table with unique records, you can follow these steps:

1. Identify the duplicate records in the existing table that you want to remove.
2. Create a new table with the same structure as the existing table, but with a unique constraint on the columns that should not have duplicates.

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CREATE TABLE new_table AS
SELECT DISTINCT *
FROM existing_table;

1. Insert the unique records from the existing table into the new table.

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INSERT INTO new_table
SELECT * FROM existing_table
MINUS
SELECT * FROM new_table;

1. Drop the existing table.

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DROP TABLE existing_table;

1. Rename the new table to the original table name.

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ALTER TABLE new_table
RENAME TO existing_table;

By following these steps, you can effectively delete duplicates in Oracle by creating a new table with unique records.

What is the difference between DELETE and TRUNCATE statements in Oracle for removing duplicates?

In Oracle, the DELETE statement is used to remove specific records from a table based on a criteria specified in the WHERE clause, whereas the TRUNCATE statement is used to remove all records from a table.

When it comes to removing duplicates, the DELETE statement can be used to remove specific duplicate rows based on a criteria such as a combination of columns or a unique identifier. This approach allows for more control over which duplicate records are removed.

On the other hand, the TRUNCATE statement will remove all records from a table, including duplicates, without the need for specifying any criteria. This approach is faster and more efficient than using the DELETE statement to remove duplicates, but it does not offer the same level of control over which records are removed.

In general, if you need to remove specific duplicate records in Oracle, it is recommended to use the DELETE statement with the appropriate criteria. If you need to remove all records from a table, including duplicates, the TRUNCATE statement is a faster and more efficient option.

How to delete duplicates in Oracle using the ROW_NUMBER() function?

You can delete duplicates in Oracle using the ROW_NUMBER() function by following these steps:

1. Identify the columns that contain duplicates.
2. Use the ROW_NUMBER() function to assign a unique number to each row within a specific group of duplicates. This is done by partitioning the result set by the columns that contain duplicates and ordering the rows within each partition.
3. Use a common table expression (CTE) to filter out the rows with row number greater than 1. This will keep only one row from each group of duplicates.
4. Use a DELETE statement to delete the duplicate rows from the table.

Here's an example query that demonstrates how to delete duplicates using the ROW_NUMBER() function:

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WITH cte AS (
    SELECT 
        *,
        ROW_NUMBER() OVER (PARTITION BY column1, column2, column3 ORDER BY column1) AS rn
    FROM 
        your_table
)
DELETE FROM cte
WHERE 
    rn > 1;

In this example:

• Replace your_table with the name of the table containing duplicates.
• Replace column1, column2, column3 with the columns where you are identifying duplicates.
• The ROW_NUMBER() function generates a unique row number for each group of duplicates based on the specified columns.
• The CTE filters out the rows with row number greater than 1, effectively deleting duplicates.
• The DELETE statement deletes the duplicate rows from the table.

Make sure to test this query in a safe environment before running it on a production database, as deleting data is a non-reversible operation.

What is the syntax for deleting duplicates in Oracle?

To delete duplicates in Oracle, you can use the following syntax:

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DELETE FROM table_name
WHERE rowid NOT IN 
(SELECT MAX(rowid)
FROM table_name
GROUP BY column1, column2, ...);

Replace table_name with the name of the table you want to remove duplicates from, and column1, column2, ... with the columns that you want to check for duplicates. This query will keep only the row with the highest rowid for each set of duplicate values in the specified columns.