How to remove duplicate records in Oracle

Oracle is one of the largest relational database management systems in the world. Its powerful functions and wide range of applications make it an indispensable part of enterprise-level applications. In these applications, data deduplication is a common task. Removing duplicate records can improve data quality and reduce storage space and query time.

In Oracle, you can use multiple methods to remove duplicate records:

1. DISTINCT keyword

Use the DISTINCT keyword to return a unique result set , which means there won't be any duplicate records. For example, the following query will return all distinct customer names:

SELECT DISTINCT CUSTOMER_NAME FROM CUSTOMERS;

2. GROUP BY clause

GROUP BY clause Used for grouping and returns a single row for each group. By combining some columns, you can find unique values. For example, the following query will return the number of customers in each city:

SELECT CITY, COUNT(*) FROM CUSTOMERS GROUP BY CITY;

3. Eliminate Duplicate Rows Function

Oracle includes several built-in functions for eliminating duplicate records, such as:

• MIN(): Returns the minimum value in the grouping.
• MAX(): Returns the maximum value in the group.
• AVG(): Returns the average value in the group.
• SUM(): Returns the sum of the values ​​in the group.

The following query will return the number of unique addresses in the customers table:

SELECT COUNT(DISTINCT ADDRESS) FROM CUSTOMERS;

4. Use window functions

The window function is a special function that calculates the value of the entire result set instead of an individual row. Use window functions to eliminate duplicate records while retaining the original data.

The following query will return the last 20 sales records sorted by sales time without retaining any duplicate sales records:

SELECT * FROM (
SELECT

ROW_NUMBER() OVER(PARTITION BY SALE_DATE ORDER BY SALE_AMOUNT DESC) RN,
SALE_ID, 
SALE_AMOUNT, 
SALE_DATE

FROM

SALES

) WHERE RN <= 20;

Summary

Oracle has many methods to delete duplicate records, including the DISTINCT keyword, GROUP BY clause, Eliminate duplicate row functions and window functions. Using these methods can improve data quality and reduce storage space and query time.

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