How Can I Find and Eliminate Duplicate Records Across Multiple Fields Using SQL?

SQL Techniques for Detecting and Removing Duplicate Records Across Multiple Columns

Maintaining data integrity often necessitates identifying and removing duplicate records based on multiple fields. This SQL guide demonstrates how to achieve this efficiently.

To pinpoint duplicate combinations across several fields, utilize this SQL query:

<code class="language-sql">SELECT field1, field2, field3, COUNT(*) AS duplicate_count
FROM table_name
GROUP BY field1, field2, field3
HAVING COUNT(*) > 1;</code>

This query groups records by the specified columns (field1, field2, field3) and counts occurrences of each unique combination. Any combination appearing more than once signifies a duplicate.

Should you need to exclude the initial occurrence of each duplicate set, a subquery offers a solution:

<code class="language-sql">SELECT field1, field2, field3
FROM table_name
WHERE (field1, field2, field3) IN
(
  SELECT DISTINCT field1, field2, field3
  FROM table_name
  GROUP BY field1, field2, field3
  HAVING COUNT(*) > 1
)
AND NOT (field1, field2, field3) IN
(
  SELECT field1, field2, field3
  FROM table_name
  ORDER BY field1, field2, field3
  LIMIT 1
);</code>

This refined query first isolates distinct duplicate combinations. It then excludes the earliest record (based on the ORDER BY clause) from each duplicate group using LIMIT 1.

These SQL techniques empower you to effectively identify and manage duplicate entries across multiple columns, enhancing data accuracy and minimizing redundancy in your database.

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