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.