GROUP BY vs. DISTINCT: When Should I Use Which for Unique Data Retrieval?

GROUP BY vs. DISTINCT: Which keyword to choose to retrieve unique data?

When retrieving unique data from a table, programmers often encounter two SQL keywords: GROUP BY and DISTINCT. While both commands eliminate duplicate values, their underlying mechanisms and potential impact are different.

In queries without aggregate functions, GROUP BY will pre-group table records based on the specified column. If the table is large, this grouping process may introduce overhead. However, because it does not perform any aggregation operations, the server usually optimizes the query so that it performs as if it were using DISTINCT.

In contrast, DISTINCT does not perform any grouping. It directly scans the entire table and dynamically removes duplicate values. While this approach is generally more efficient when working with smaller tables, it can become performance-intensive as the table size increases.

It is important to note that using GROUP BY without an aggregate function solely to eliminate duplicate values ​​is generally not recommended. Although the server may optimize the query, it is recommended to use DISTINCT when retrieving unique values ​​to avoid potential pitfalls and maintain code clarity.

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