How Can I Efficiently Count Unique Values in a SQL Column?

Finding the Number of Unique Values in a SQL Column

Question:

While selecting distinct values from a specific column is easily achievable using the SELECT DISTINCT statement, determining the row count for these distinct values requires further consideration.

Subquery Dilemma:

One approach considered was utilizing a subquery, effectively employing SELECT DISTINCT within an inner subquery and COUNT in the outer query. However, this method introduces additional levels of complexity and potential performance issues.

Elegant Solution: DISTINCT within COUNT

A more efficient and concise approach involves utilizing the DISTINCT keyword within the COUNT aggregate function. This technique filters out duplicate values before applying the counting operation.

SELECT COUNT(DISTINCT column_name) AS unique_count FROM table_name

This statement directly calculates the number of unique values in the specified column, providing the desired count without the need for a subquery. By cleverly incorporating DISTINCT within COUNT, the query ensures that only distinct values are counted, accurately reflecting the cardinality of the values in the column.

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