Handling duplicates is a common challenge in database management. PostgreSQL's DISTINCT clause offers a straightforward way to ensure that your query results are free from duplicate entries. This article provides a concise guide on using DISTINCT to maintain clean data.
How to Use PostgreSQL DISTINCT
To filter out duplicates from your query results, utilize the SELECT DISTINCT clause. Here’s a quick look at the syntax:
SELECT DISTINCT column1, column2
FROM table_name;
Single column
SELECT DISTINCT column1
FROM table_name;
Multiple columns
SELECT DISTINCT column1, column2
FROM table_name;
This returns unique combinations of column1 and column2.
FAQ
Why use DISTINCT in PostgreSQL?DISTINCT is used to filter out duplicate rows, ensuring that each row in the result set is unique.
How is DISTINCT applied in a query?
Include DISTINCT immediately after SELECT in your query, followed by the columns you want to evaluate for uniqueness.
Can DISTINCT work with multiple columns?
Yes, it evaluates the combination of specified columns, returning only unique combinations.
Does DISTINCT change the order of results?
No, the order remains unaffected by DISTINCT. To sort results, use ORDER BY.
Conclusion
The DISTINCT clause in PostgreSQL is essential for eliminating duplicate rows in your query results. For an in-depth guide and more examples, read the article PostgreSQL DISTINCT: Removing Duplicate Rows from a Result Set.