Skip to main content
🐘

​
PostgreSQL

The world’s most advanced open source database. SQL fluency, indexes, and transaction isolation are must-knows.

​
Topics

CREATE & INSERT

CREATE TABLE, data types, constraints, INSERT, and upserts.

SELECT Queries

SELECT, WHERE, GROUP BY, HAVING, subqueries, and CTEs.

Calculated Columns

Arithmetic expressions, CASE, type casting, and date functions.

String Functions

Concatenation, pattern matching, regex, and text manipulation.

Joins

INNER, LEFT, RIGHT, FULL OUTER joins with examples.

Indexes

B-tree, Hash, GIN, EXPLAIN ANALYZE, and index design.

Transactions

ACID properties, isolation levels, and deadlocks.
◆ ACID Properties
Atomicity — all or nothing. Consistency — data stays valid. Isolation — transactions don’t interfere. Durability — committed data survives crashes.
💡 Interview Tip
Practice writing window functions (ROW_NUMBER, RANK, LAG, LEAD) — they’re a common senior-level SQL interview topic that trips up many candidates.