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.