In MySQL regular expressions, the dollar sign $ is an anchor that matches the end of a string. It ensures that the pattern preceding the $ occurs at the end of the string.

Key Points About the Dollar Sign ($) Symbol

1
End Anchor: pattern$ matches strings that end with the specified pattern.
2
Position-Specific Matching: Unlike simple substring matching, $ ensures the match occurs at the very end of the string.
3
Combining with Character Classes: You can use it with brackets, e.g., [0-9]{4}$ matches strings ending with four digits.
4
Use in Validation: Useful for validating formats that must end in a specific way, such as file extensions, postal codes, or numeric codes.

When used in a SELECT query with REGEXP, $ helps narrow down matches to strings ending with specific characters or patterns.

Example: Match Emails Ending with '.com'

Example: Match Phone Numbers Ending with '00'

Difficulty: 5/10

Topics: REGEXP syntax, pattern anchoring, MySQL regex behavior

Scenario Questions

0-2 years experience

1
You need to write a query that returns rows where the email column ends with '.org'. How would you use the $ anchor in a MySQL REGEXP pattern to achieve that?
2
If you run SELECT * FROM users WHERE username REGEXP 'admin$'; what rows will be matched and why?
3
What would happen if you omitted the $ in the previous pattern—how would the result set change?

2-5 years experience

1
Your team notices that a query using REGEXP 'error$' is missing some log entries that actually end with 'error' but have a trailing newline character. Explain why this is happening and how you would fix it.
2
During a migration to MySQL 8.0, a stored procedure that relied on REGEXP patterns with $ started returning unexpected rows. What changes in regex handling could cause this, and how would you debug it?
3
You need to filter product codes that must end with exactly three digits. Write the REGEXP pattern and discuss any trade‑offs regarding index usage.

5-8 years experience

1
Design a logging aggregation service that stores raw log lines in MySQL and allows users to define custom REGEXP filters, including end‑of‑line anchors. What performance considerations arise from using $ in patterns, and how would you mitigate them at scale?
2
Your production system experiences a slowdown when many users run queries with REGEXP patterns that include $ on a large table. Explain why $ can affect query planning and propose architectural changes (e.g., generated columns, full‑text indexes) to improve throughput.
3
How would you ensure that regex patterns with $ behave consistently across different MySQL versions and collations in a multi‑region deployment?

8+ years experience

1
The company is moving from MySQL to a distributed SQL platform that supports a different regex engine. How would you approach a migration strategy that preserves the semantics of $ anchors in existing queries, and what tooling or testing would you put in place?
2
Across several microservices, teams have built feature flags that rely on MySQL REGEXP patterns with $ to match request URLs. As a staff engineer, how would you standardize pattern definitions to avoid bugs and support future refactoring to a centralized rule engine?
3
Discuss the long‑term maintenance implications of embedding $‑anchored regexes directly in application code versus abstracting them into configuration, considering version upgrades and observability.

Follow-up Questions

❓How would you verify that your $‑anchored pattern works for edge cases like trailing whitespace?
❓What impact does using $ have on MySQL's ability to use indexes for REGEXP queries?
❓Can you describe a situation where $ might not behave as expected due to data encoding or collation?