Oracle database query skills: get only one piece of duplicate data

Oracle database query skills: only obtain one piece of duplicate data, specific code examples are required

In actual database queries, we often encounter the need to obtain duplicate data from Get the only piece of data. This article will introduce how to use Oracle database techniques to obtain only one record in duplicate data, and provide specific code examples.

Scenario description

Suppose we have a table named employee, which contains employee information. There may be duplicate employee information. We need to query any record of all duplicate employee information, rather than obtain all duplicate employee information.

Query implementation

We can use the window function ROW_NUMBER() in Oracle database combined with the PARTITION BY statement to achieve this requirement. The specific implementation idea is to assign a serial number to each record, and then filter out the record with the serial number 1 to obtain the first record in each set of repeated data.

The following is a specific code example based on the above idea:

SELECT *
FROM (
    SELECT 
        e.*,
        ROW_NUMBER() OVER (PARTITION BY e.employee_id ORDER BY e.employee_id) AS rn
    FROM employee e
) tmp
WHERE rn = 1;

In the above code, a serial number rn is first added to each record through a subquery, and Group based on employee_id field. Then filter out the record with serial number 1 in the external query, and you can get the first record in each set of repeated data.

Example Description

Assume that the employee table has the following structure:

employee_id	name	department
1	张三	Technical Department
2	李四	Sales Department
3	王五	Finance Department
1	张三	Technical Department
2	李思	Sales Department

After executing the above code example, the following results will be returned:

##1张三Technical Department 2李四 Sales Department3王五Finance Department

employee_id	name	department

As can be seen from the above example, we successfully obtained the first record in each set of data from the duplicate data, achieving meet our query needs.

Summary

This article introduces the implementation method of obtaining only one record in duplicate data in Oracle database, and provides specific code examples. By using the window function

ROW_NUMBER() and the PARTITION BY statement, we can easily achieve this requirement, improving query efficiency and data processing accuracy. I hope this article will be helpful to you in your actual database query work.

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