When working with multiple tables in a database, it is often necessary to perform calculations that involve values from different tables. Calculating the average of columns from multiple tables can be achieved using SQL.

Let’s consider a scenario where we have two tables - “sales” and “expenses”. Each table has a column called “amount” that represents the amount of money involved.

To calculate the average of the “amount” column from both tables, we can use the following SQL query:

SELECT AVG(amount) AS average_amount
FROM (
  SELECT amount FROM sales
  UNION ALL
  SELECT amount FROM expenses
) AS combined_table;

In this query, we are performing a UNION ALL operation to combine the “amount” columns from both tables into a single resultset. Then, we apply the AVG function to calculate the average of the combined “amount” values. We alias the calculated average as “average_amount” for clarity.

By executing this SQL query, you will get the average value of the “amount” column from both the “sales” and “expenses” tables.

However, it’s important to note that the columns being averaged should have compatible data types in both tables. Otherwise, you might encounter errors or unexpected results.

Conclusion

Calculating the average of columns from multiple tables in SQL can be achieved by using the UNION ALL operation to combine the columns from different tables and then applying the AVG function. This allows you to perform calculations that involve values from multiple tables within your SQL queries.

#SQL #Database #Average #Tables