Troubleshooting SQL Queries: Understanding the WHERE Function and Overcoming Case Sensitivity Issues

Understanding the SQL WHERE Function and Why It’s Not Returning Any Results

As a technical blogger, it’s not uncommon to come across puzzling issues with SQL queries. In this post, we’ll delve into an example where none of the expected results are being returned, despite the query seemingly correct. We’ll explore the concepts behind the WHERE function and provide step-by-step guidance on how to troubleshoot this issue.

Understanding the SQL LIKE Operator

The LIKE operator is used in SQL to search for a specified pattern within a column or string of text. When using the LIKE operator, it’s essential to understand the syntax and the different types of wildcards available.

In MySQL (the database management system used in this example), there are two main types of wildcards:

Literal Wildcard (%): The % wildcard matches zero or more characters. It’s often used at the start and end of a string to match any sequence of characters.
Positional Wildcard (\_): The \ _ wildcard matches a single character.

In this example, we’re using the LIKE operator with the % wildcard. However, there’s an issue with the query that prevents it from returning any results.

The Problem: Case Sensitivity

Notice how the column name 'courses' and the keyword 'SEP 2022 - Global Design%' are written in different cases. In this case, we can see that the LIKE operator is case-sensitive. This means that if the query was using a lowercase wildcard, it might have returned some results.

However, there’s an issue with the actual SQL syntax used in the question (the square brackets around column names seem incorrect and would typically not be necessary).

In standard SQL, column names are written in lowercase and do not require quotes to enclose them. For this example, let’s assume that ‘courses’ is a column name without any leading/trailing space or unnecessary quotation marks.

Let’s now correct the query:

SELECT dealname, email, courses
FROM `airbyte-bigquery.hubspot_airbyte.deals_properties`
WHERE closedate > '2022-09-01' AND courses LIKE '%SEP 2022 - Global Design%'

The Solution: Using the LOWER() Function

To overcome the issue with case sensitivity and to make our query more robust, we can use the LOWER() function. The LOWER() function returns the string value of a column in lowercase.

SELECT dealname, email, courses
FROM `airbyte-bigquery.hubspot_airbyte.deals_properties`
WHERE closedate > '2022-09-01' AND LOWER(courses) LIKE '%sep 2022 - global design%'

Now the query should return all rows where the column 'courses' contains the specified keyword, regardless of case.

Additional Tips and Best Practices

Always Test Your Queries: It’s crucial to test your SQL queries thoroughly before relying on them in production.
Use Meaningful Table Names: Choose meaningful table names that accurately describe their content. This will make your queries more readable and easier to maintain.
Follow Standard SQL Syntax: Standard SQL syntax helps ensure that your queries are portable across different databases.

Conclusion

In this post, we explored a puzzling issue where an SQL query was not returning any results, despite seeming correct. We delved into the concepts behind the WHERE function and explained how using the LOWER() function can make our queries more robust by overcoming case sensitivity issues.

By following best practices, testing your queries thoroughly, and choosing meaningful table names, we can write efficient and effective SQL queries that deliver reliable results in real-world applications.

Last modified on 2023-07-23