How does MySQL evaluate operator precedence when multiple operators are used in a single expression?

0-2 years experience

1. 1You need to calculate a commission with `salary + bonus * tax_rate`. If you forget the parentheses, what value does MySQL return and why?
2. 2In a WHERE clause you write `status = 'active' OR is_admin = 1 AND last_login > NOW() - INTERVAL 7 DAY`. Which part is evaluated first and what rows will be returned?
3. 3Write a simple SELECT that uses both `+` and `>` operators. Explain the order MySQL uses to evaluate them.

2-5 years experience

1. 1A query meant to exclude inactive users is returning too many rows. The clause is `active = 0 OR role = 'admin' AND created_at > '2023-01-01'`. Explain how operator precedence caused the bug and how you'd rewrite it.
2. 2When building a reporting view you need a CASE expression that mixes arithmetic and logical checks. How do you guarantee the intended order without relying on MySQL's default precedence?
3. 3Does the order of operators in a WHERE condition affect whether MySQL can use an index? Give an example where precedence prevents index usage and how to fix it.

5-8 years experience

1. 1Your team is migrating a legacy codebase that contains many complex WHERE clauses without parentheses. Outline a strategy to audit, refactor, and test those queries to eliminate precedence bugs while keeping the service up.
2. 2Explain how MySQL handles mixed‑type expressions, such as `price + '10'` combined with logical operators. What pitfalls arise in a high‑traffic API?
3. 3Design a query‑builder library that automatically respects MySQL operator precedence. What data structures or algorithms would you use to ensure generated SQL is correct?

8+ years experience

1. 1Your organization wants a company‑wide policy to enforce explicit parentheses in all SQL expressions. Propose tooling, CI linting, and review processes that achieve this without breaking existing services.
2. 2A legacy rule engine stores raw MySQL expressions that rely on default precedence, and a version upgrade introduced subtle bugs. How would you redesign the engine to be version‑agnostic and maintainable?
3. 3Different teams use MySQL and PostgreSQL, which have differing precedence for some operators (e.g., `||`). How would you abstract query generation to avoid cross‑database precedence issues?