Indexes

Summary

Data structures that speed up lookups on specific columns, at the cost of extra storage and slightly slower writes — the single biggest lever for query performance.

How to Learn This

1Run a query with and without an index, using `EXPLAIN`, and compare the execution plan.
2Learn when to index a column: frequently filtered/joined columns are good candidates.
3Understand why over-indexing every column can hurt write performance.

Joins

Normalization

More topics in SQL Databases

Relational Database Concepts SQL Basics (SELECT, INSERT, UPDATE, DELETE)Joins Normalization Transactions ACID Properties PostgreSQL MySQL Constraints & Keys Views Stored Procedures Database Design & ER Diagrams Migrations

Stuck on this topic? Ask an Insider

Get 1:1 guidance from people who've walked this exact path — free on the InsideEdge app.

Download