How Can I Count Distinct Values in a SQL Column?

Counting Distinct Values in SQL Columns

When working with SQL databases, it is often necessary to determine the number of distinct values in a specific column. To achieve this, there are two common approaches:

• SELECT DISTINCT: This query retrieves all distinct values in a column:

  SELECT DISTINCT column_name FROM table_name;

• SELECT with GROUP BY: This query groups the results by the column, effectively providing a unique count for each distinct value:

  SELECT column_name FROM table_name GROUP BY column_name;

However, neither of these methods provides a direct row count of distinct values. To obtain this information, it is necessary to utilize the DISTINCT keyword within the COUNT aggregate function:

SELECT COUNT(DISTINCT column_name) AS some_alias FROM table_name

This query counts only the distinct values in the specified column, resulting in a single row containing the count. The some_alias is a placeholder that can be replaced with any desired alias for the result.

By utilizing this approach, it is straightforward to determine the number of distinct values in a column without the need for subqueries or additional processing.

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