How to Remove the Duplicate Record In Oracle Query?

To remove duplicate records in an Oracle query, you can use the DISTINCT keyword in your SELECT statement. This will eliminate duplicate rows and only return unique records based on the specified columns in the query. Additionally, you can use the ROW_NUMBER() function to assign a unique row number to each record and then filter out the duplicates by selecting only the rows with a row number of 1. Another method is to use the GROUP BY clause with aggregate functions to group the data by specific columns and remove duplicates in the process. These are some common techniques used to remove duplicate records in an Oracle query.

What are the different ways to handle duplicate records in Oracle?

1. Use ROWID: The ROWID pseudo column can be used to identify duplicate records in a table. You can use ROWID to identify and delete duplicate records.
2. Use UNIQUE and PRIMARY KEY constraints: You can prevent duplicate records from being inserted into a table by using the UNIQUE and PRIMARY KEY constraints. These constraints ensure that each record in a table is unique based on certain columns.
3. Use DISTINCT keyword: When querying data, you can use the DISTINCT keyword to remove duplicate records from the result set. This will only display one instance of each record in the output.
4. Use ROW_NUMBER() function: You can use the ROW_NUMBER() function to assign a unique number to each row in a table. By partitioning the data based on certain columns and ordering it appropriately, you can identify and remove duplicate records.
5. Use MERGE statement: The MERGE statement can be used to update or insert records based on a specified condition. By merging data from a source table to a target table, you can handle duplicate records effectively.
6. Use subqueries: You can use subqueries to identify and handle duplicate records. By using a subquery to filter out duplicate records, you can delete or update them as needed.

How can you combine multiple columns to identify duplicate records in Oracle?

To combine multiple columns to identify duplicate records in Oracle, you can use the GROUP BY clause with the HAVING clause in a SQL query.

Here's an example query:

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SELECT column1, column2, column3, COUNT(*)
FROM your_table
GROUP BY column1, column2, column3
HAVING COUNT(*) > 1;

This query combines the values in columns 1, 2, and 3 and groups them together. The HAVING clause filters the grouped records to only show those that appear more than once, indicating duplicate records.

How can you delete duplicate records in Oracle database?

There are several ways to delete duplicate records in an Oracle database:

1. Using the ROWID pseudocolumn: You can use the ROWID pseudocolumn to identify duplicate records and delete them. Here's an example query that deletes duplicate records from a table called "table_name":

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

Replace "table_name" with the name of your table and "column1, column2, ..." with the columns that you want to check for duplicates.

1. Using the RANK() window function: You can use the RANK() window function to assign a rank to each record based on a specific criteria and then delete records with a rank higher than 1. Here's an example query that deletes duplicate records from a table called "table_name" based on a column called "column1":

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DELETE FROM table_name
WHERE ROWID IN (
  SELECT ROWID
  FROM (
    SELECT ROWID, RANK() OVER (PARTITION BY column1 ORDER BY column1) rnk
    FROM table_name
  )
  WHERE rnk > 1
);

Replace "table_name" with the name of your table, "column1" with the column that you want to check for duplicates, and "ORDER BY column1" with the criteria for ranking the records.

1. Using the DELETE statement with a self-join: You can use a self-join in a DELETE statement to delete duplicate records. Here's an example query that deletes duplicate records from a table called "table_name" based on a column called "column1":

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DELETE t1
FROM table_name t1
JOIN table_name t2
ON t1.column1 = t2.column1
WHERE t1.ROWID > t2.ROWID;

Replace "table_name" with the name of your table and "column1" with the column that you want to check for duplicates.

Remember to always backup your data before deleting any records to avoid accidental data loss.

How to use the analytic functions like PARTITION BY to remove duplicate records in Oracle?

To use the analytic functions like PARTITION BY to remove duplicate records in Oracle, you can follow these steps:

1. Identify the columns that contain duplicate records in your table.
2. Use the ROW_NUMBER() function with the PARTITION BY clause to assign a unique row number to each record within a partition based on the duplicate columns.
3. Write a query to select only the records where the row number equals 1, effectively removing the duplicate records.

Here is an example SQL query that demonstrates this process:

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WITH cte AS (
  SELECT 
    *,
    ROW_NUMBER() OVER (PARTITION BY column1, column2, ... ORDER BY some_column) AS rn
  FROM your_table
)
SELECT *
FROM cte
WHERE rn = 1;

In this query:

• Replace column1, column2, ... with the columns that contain duplicate records.
• Replace some_column with a column that can be used to determine the order of the records within each partition. If you do not have a specific order requirement, you can omit the ORDER BY clause.
• Replace your_table with the name of your table.

By using the PARTITION BY clause along with the ROW_NUMBER() function in a Common Table Expression (CTE), you can eliminate duplicate records from your table in Oracle.

What is the difference between UNION and UNION ALL in Oracle for removing duplicates?

In Oracle, the UNION operator is used to combine the result sets of two or more SELECT statements into a single result set. When using the UNION operator, duplicate rows are automatically removed from the result set.

On the other hand, the UNION ALL operator also combines the result sets of two or more SELECT statements into a single result set. However, unlike the UNION operator, the UNION ALL operator does not remove duplicates. It simply appends the result sets together, including any duplicate rows.

Therefore, if you want to remove duplicates from the result set, you should use the UNION operator. If you do not want to remove duplicates and simply want to combine the result sets, you should use the UNION ALL operator.