Complex Aggregates Require an Alias
When using complex aggregate functions in a SQL query, it is necessary to provide an alias for the result of the aggregate calculation. An alias is a name given to the computed value which can be referenced in the query’s output or used in subsequent computations.
Complex aggregate functions, like COUNT, SUM, AVG, etc., perform calculations on a set of rows and return a single value representing the result. Here’s an example to illustrate the need for an alias:
SELECT COUNT(*) FROM orders WHERE status = 'completed'
In this example, the query calculates the number of orders with a status of ‘completed’. However, without providing an alias, it can be difficult to refer to the result in the output or perform additional calculations. To solve this, we can assign an alias to the result:
SELECT COUNT(*) AS completed_orders_count FROM orders WHERE status = 'completed'
Now, we have assigned the alias completed_orders_count to the result of the COUNT function. This alias can be used to reference the aggregate value in the output:
SELECT CONCAT('Number of completed orders: ', completed_orders_count) FROM orders_summary
In the above query, the alias completed_orders_count is concatenated with a string to form the output.
Providing an alias is not only useful for readability and output purposes, but also when using the result of a complex aggregate in further calculations:
SELECT AVG(completed_orders_count) FROM order_stats
In the example above, we are calculating the average value of the completed_orders_count column in the order_stats table.