How to Find and Count Duplicate Values in an Oracle Table Column?

Efficiently Identifying and Counting Duplicate Values in Oracle Tables

Maintaining data integrity is crucial when dealing with extensive datasets. Duplicate values are a common concern that can significantly impact data accuracy. This article provides a concise and effective SQL solution for locating and counting duplicate entries within an Oracle database table.

Challenge:

How can you pinpoint and quantify duplicate entries within a specific column of an Oracle table?

Solution:

The most efficient SQL query to identify and count duplicate values in an Oracle table is:

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

Explanation:

• *`SELECT column_name, COUNT() AS DuplicateCount**: This selects the column containing duplicates and counts their occurrences, labeling the count asDuplicateCount`.
• FROM table_name: Specifies the table to search for duplicates.
• GROUP BY column_name: Groups rows based on the specified column.
• *`HAVING COUNT() > 1`**: Filters results to show only columns with more than one instance, indicating duplicates.

Illustrative Example:

Let's assume a JOBS table with a JOB_NUMBER column. The query would be:

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

This query will output a list of JOB_NUMBER values appearing more than once, alongside their respective counts, facilitating the quick identification and resolution of data redundancy.

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