How to Format SQL Queries in Python: Best Practices, Gotchas, and Real-World Examples

Stop writing SQL strings that look like a ransom note. Here's how to write queries that are readable, safe, and maintainable. The Problem With "Good Enough" SQL Formatting Most Python developers start here: user_id = 5 query = " SELECT * FROM users WHERE id = " + str ( user_id ) cursor . execute ( query ) It works. Until it doesn't — and when it breaks, it breaks badly : SQL injection, cryptic errors from mismatched types, and queries that take 45 minutes to debug at 2am. Let's fix that, permanently. 1. Never Concatenate User Input — Use Parameterized Queries This is rule #1 and it's non-negotiable. ❌ The Wrong Way (SQL Injection Waiting to Happen) username = request . args . get ( " username " ) # Could be: ' OR '1'='1 query = f " SELECT * FROM users WHERE username = ' { username } '" cursor . execute ( query ) If username is ' OR '1'='1 , your entire users table just got exposed. ✅ The Right Way: Parameterized Queries username = request . args . get ( " username " ) # psycopg2 (PostgreSQL) cursor . execute ( " SELECT * FROM users WHERE username = %s " , ( username ,)) # sqlite3 cursor . execute ( " SELECT * FROM users WHERE username = ? " , ( username ,)) # SQLAlchemy Core from sqlalchemy import text result = conn . execute ( text ( " SELECT * FROM users WHERE username = :name " ), { " name " : username }) The database driver handles escaping. You never touch it. This pattern is immune to SQL injection by design. Gotcha: Note the trailing comma in (username,) . Without it, Python treats the string as an iterable and passes each character as a separate parameter. This is one of the most common beginner bugs. # 💥 Bug: passes ('a', 'l', 'i', 'c', 'e') instead of ('alice',) cursor . execute ( " SELECT * FROM users WHERE username = %s " , ( username )) # ✅ Correct: single-element tuple cursor . execute ( " SELECT * FROM users WHERE username = %s " , ( username ,)) 2. Multi-Line Queries: Triple Quotes + Consistent Indentation For anything longer than one clause, use tri