How can you ensure a query returns the correct results?

1 Test your queries

Before you run your queries on a live database, you should test them on a sample or a copy of the data. This way, you can check if your queries are syntactically correct, if they match your expected output, and if they run efficiently. You can use tools such as SQL Fiddle, DB Fiddle, or SQL Server Management Studio to test your queries online or offline. You can also compare your results with other sources of data, such as reports, spreadsheets, or external databases, to verify their validity.

2 Use comments and formatting

Another way to ensure that your queries return the correct results is to use comments and formatting to make your queries more readable and understandable. Comments can help you document your logic, explain your assumptions, and highlight any potential issues or limitations. Formatting can help you organize your queries into sections, indent your code, and use consistent naming conventions. You can use tools such as SQL Formatter, SQL Beautifier, or SQL Pretty Printer to format your queries automatically or manually.

3 Review your logic and calculations

Sometimes, your queries may return the correct results, but they may not reflect the true meaning or intention of your data. For example, you may have used the wrong operators, functions, or aggregations, or you may have overlooked some conditions, filters, or joins. To avoid these pitfalls, you should review your logic and calculations carefully and make sure they align with your business rules, requirements, and expectations. You can use tools such as SQL Debugger, SQL Trace, or SQL Profiler to debug your queries and identify any errors or anomalies.

5 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?