JOIN — Python Technical Interview Questions & Answers

JOIN

JOIN

  • JOIN is about talking to a database from Python. Pattern is always: connect → cursor → execute → fetch or commit → close.
  • For JOIN: use ? placeholders (or the driver’s params). Never build SQL with + user text — that is injection. sqlite3 is in the stdlib for practice; MySQL/Mongo need a driver.
  • JOIN on the board: insert Asha, select her back, print the name. Same idea on MySQL. Close the connection.
  • Output: ('Asha', 90). JOIN on id.

Technical Interview Tip: Steps in order: connect → execute → fetch/commit → close. Mention placeholders.

Code Examples for JOIN

Example

# JOIN
import sqlite3
con = sqlite3.connect(":memory:")
cur = con.cursor()
cur.execute("create table s(id integer, name text)")
cur.execute("create table m(sid integer, marks integer)")
cur.execute("insert into s values(1,'Asha')")
cur.execute("insert into m values(1,90)")
print(cur.execute("select s.name, m.marks from s join m on s.id=m.sid").fetchone())
con.close()

Output: ('Asha', 90). JOIN on id.

How to Explain JOIN to an Interviewer

Explain JOIN as if you are teaching a junior — definition, then one tiny script.

JOIN uses connect + cursor + SQL/API. JOIN — parameterized queries. Never + user text into SQL.

What does the example print, and why?

('Asha', 90)

What mistake do freshers make with JOIN?

JOIN — commit after write. close when done.