How to Find Duplicate Values in Oracle Tables Using SQL?

Find duplicate values ​​in Oracle table

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

Query building:

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

<code class="language-sql">SELECT column_name, COUNT(column_name)
FROM table_name
GROUP BY column_name
HAVING COUNT(column_name) > 1;</code>

Instructions:

• COUNT aggregation: The COUNT function is applied to the target column, aggregates and counts its occurrences.
• Group by column: The GROUP BY clause partitions the results by the column of interest, grouping identical values ​​together.
• Filter by count: The HAVING clause applies a filter to select only values ​​that occur more than once (i.e. duplicate values).

Example usage:

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

<code class="language-sql">SELECT JOB_NUMBER, COUNT(JOB_NUMBER)
FROM JOBS
GROUP BY JOB_NUMBER
HAVING COUNT(JOB_NUMBER) > 1;</code>

The output will show a list of JOB_NUMBER and the number of times their respective occurrences occurred, allowing you to quickly identify any duplicates.

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