# Relational Databases: Using Calculations

## Relational Databases: Using Calculations

Understanding Calculations in Relational Databases

• Calculations in relational databases are mathematical operations used to generate results from numerical data stored in the database.
• These calculations are crucial in deriving valuable insights from data, such as summaries, averages, and trends.

Basic Database Calculations

• Most common basic calculations in relational databases include addition, subtraction, multiplication, and division of numerical fields in a database.
• These calculations often form the basis for more complex operations and data analysis.

Use of Aggregate Functions

• Aggregate functions are used in SQL to compute a single result from a set of input values, such as `SUM()`, `AVG()`, `MAX()`, `MIN()`, and `COUNT()`.
• For example, `SUM(column_name)` function would return the sum of all values in the provided column.

Conditional Calculations with CASE Statement

• A CASE statement in SQL can be used to perform conditional calculations.
• This allows different calculations to be performed on a row depending on whether it meets certain criteria. For example, one could calculate a different tax percentage based on the value of a ‘Salary’ field.

Using the GROUP BY Clause in Calculations

• SQL’s `GROUP BY` clause allows users to group rows that have the same values in specified columns into aggregated data.
• This is useful for applying calculations to subsets of data. For example, one could calculate the average salary of employees in each department using `AVG(Salary)` in conjunction with a `GROUP BY Department` clause.

Deriving New Columns through Calculations

• It’s possible to generate new columns as result of calculations.
• For instance, the SQL expression `SELECT Salary, (Salary * 0.1) as 'Tax' FROM Employees;` would generate a new ‘Tax’ column that contains each employee’s tax calculated at 10% of their salary.

Testing Calculations

• Testing is vital to ensure that calculations carry out the correct operation and produce the expected results.
• This involves inserting known data, applying the calculation, and checking the results against expected outcomes. Any discrepancies should be identified and resolved.

Calculations and Database Performance

• Complex calculations can sometimes have an impact on overall database performance.
• To maintain efficient operation, it’s recommended to optimise calculations by minimising their complexity where possible, and by performing calculations during off-peak usage times.