10 Practical SQL Query Optimization Techniques for Data Engineering Interviews

Optimizing SQL query performance is a core requirement in data engineering interviews. Practice live SQL queries at /sql/.

1. SARGable Query Predicates

-- Bad (Non-SARGable):
SELECT * FROM orders WHERE YEAR(order_date) = 2026;

-- Good (SARGable):
SELECT * FROM orders WHERE order_date >= '2026-01-01' AND order_date < '2027-01-01';

Wrapping an indexed column inside a scalar function like YEAR() prevents the database planner from using B-Tree index lookups, forcing expensive full table scans!