Find duplicate values ​​in Oracle table

In Oracle databases, identifying duplicate values ​​in table columns is critical to ensuring data accuracy and integrity. For this purpose, the most efficient SQL statements utilize aggregation and conditional filtering.

Query construction:

The SQL query to find duplicate values ​​is as follows:

SELECT column_name, COUNT(column_name)
FROM table_name
GROUP BY column_name
HAVING COUNT(column_name) > 1;

illustrate:

• COUNT Aggregation: The COUNT function is applied to the target column, aggregated and calculated the number of occurrences.
• Group by column: The GROUP BY clause partitions the results by column of interest and combines the same values ​​together.
• Filter by count: The HAVING clause applies a filter, selecting only values ​​that appear multiple times (i.e., repeat values).

Example usage:

To identify duplicate JOB_NUMBER in JOBS table, you can use the following query:

SELECT JOB_NUMBER, COUNT(JOB_NUMBER)
FROM JOBS
GROUP BY JOB_NUMBER
HAVING COUNT(JOB_NUMBER) > 1;

The output will display a list of JOB_NUMBER and its respective occurrences, allowing you to quickly identify any duplicates.