Queries — SQL Technical Interview Questions & Answers

Queries

Queries

  • A query is a SQL statement that asks for or changes data. The ones you must type without thinking: SELECT, INSERT, UPDATE, DELETE. Plus CREATE for structure. People also say ‘query’ only for SELECT — in a viva, say DML vs DDL if they split hairs.
  • SELECT reads. INSERT adds a row. UPDATE changes a row. DELETE removes a row. Always practise SELECT with the same WHERE before UPDATE/DELETE.
  • Read a query in this order in your head: FROM (which table) → WHERE (which rows) → SELECT (which columns). GROUP BY / HAVING / ORDER BY come after that story.
  • Trap: SELECT * in every answer. Name columns. Trap: UPDATE without WHERE — whole table becomes 0 marks.
  • On the example next to this theory: Queries: create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Technical Interview Tip: Name CRUD. Warn: no WHERE on UPDATE. Prefer listing columns.

Code Examples for Queries

Queries — sample query

-- Queries
CREATE TABLE demo (
  id INTEGER PRIMARY KEY,
  label TEXT NOT NULL,
  qty INTEGER DEFAULT 0
);
INSERT INTO demo (id, label, qty) VALUES
  (1, 'alpha', 2),
  (2, 'beta', 5);
SELECT label, qty FROM demo WHERE qty >= 2 ORDER BY qty DESC;

Queries: create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

How to Explain Queries to an Interviewer

What are the four data queries?

SELECT, INSERT, UPDATE, DELETE

In what order do you read a SELECT?

FROM, then WHERE, then SELECT columns