# 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.