In MySQL, you can use the REGEXP operator with the caret ^ symbol to match strings that start with a specific letter. The ^ anchor ensures that the pattern occurs at the beginning of the string.

Key Points for Matching Strings Starting with a Letter

1
Start Anchor: Use ^ before the letter to indicate the start of the string, e.g., ^A matches strings starting with 'A'.
2
Case Sensitivity: By default, REGEXP is case-insensitive for non-binary strings. Use BINARY for case-sensitive matches.
3
Character Classes: You can match multiple letters by using brackets, e.g., ^[AB] matches names starting with 'A' or 'B'.
4
Combining with Wildcards: You can use .* after the starting letter to match the rest of the string, e.g., ^A.* matches all strings starting with 'A'.

Using this approach allows you to filter or search rows based on the first character of a string column efficiently.

Example: Match Names Starting with 'A'

Example: Match Names Starting with 'A' or 'B'

Example: Case-Sensitive Match for Names Starting with 'A'

Scenario Questions

0-2 years experience

1We have a table `employees` with a column `first_name`. How would you write a MySQL query to list all rows where the name starts with the letter 'A' using REGEXP?
2If you run `SELECT * FROM employees WHERE first_name REGEXP '^A';` and get no results, what are some reasons that could happen?
3What would you change in the query if you needed case‑insensitive matching for names starting with 'a'?

2-5 years experience

1Our product team wants a UI filter to show customers whose last name begins with a user‑selected letter. How would you implement that in MySQL using REGEXP, and what trade‑offs would you consider versus using LIKE?
2During a code review you notice a query that uses `REGEXP '^A'` on a large `users` table and it's causing a slowdown. How would you investigate and improve its performance?
3Suppose the requirement changes to support Unicode characters that look like 'A' (e.g., Cyrillic А). How would you adapt the REGEXP pattern?

5-8 years experience

1We are migrating a legacy reporting system that currently uses `LIKE 'A%'` on a 500 M‑row table to a new microservice that uses REGEXP for more complex patterns. What indexing strategies or schema changes would you propose to keep the query fast at scale?
2Your team needs to expose an API that returns rows where a free‑text column matches a dynamic prefix supplied by the caller. How would you safely construct the REGEXP pattern to avoid injection and ensure performance?
3If the database needs to support both MySQL 5.7 and 8.0, and REGEXP syntax differs slightly, how would you design a compatibility layer for prefix searches?

8+ years experience

1Across the organization we want to standardize prefix searches on several high‑traffic tables. How would you design a shared library or abstraction that handles REGEXP prefix queries, indexing, and monitoring, while allowing teams to evolve their schemas?
2During a multi‑year data warehouse consolidation, you discover many ad‑hoc queries using `REGEXP '^A'`. What strategy would you use to refactor these queries, assess impact, and migrate to a more maintainable solution?
3How would you evaluate the trade‑offs of moving prefix searches from MySQL to an external search service like Elasticsearch for global scale, considering latency, consistency, and operational overhead?

Follow-up Questions

How would you test that your REGEXP query returns the correct rows?
What edge cases could cause the pattern to miss expected matches?
How would you monitor the performance impact of this query in production?

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