Store and query data efficiently.
Before writing a query, understand why we store data in a database at all.
Tables, rows, and columns are how relational databases think.
The command you'll write most — retrieving exactly the data you need.
Big result sets are useless without proper ordering and showing the part that matters.
Reading isn't enough — you must write, modify, and delete safely.
Designing a table right from the start saves a world of pain later.
Real data lives across many tables — JOINs bring it together.
Analysis starts with: how many? what's the total? the average?
Sometimes you need a query's result inside another — it unlocks a lot.
Good design prevents duplicate, inconsistent data — the basis of a healthy database.
Constraints stop bad data at the door — your shield against chaos.
A view stores a complex query under a simple name you reuse like a table.
An index is the difference between a query in milliseconds and one in minutes.
When half a bank transfer succeeds, you learn why transactions are life or death.
Moving repeated logic into the database cuts duplication and can boost performance.
A correct query isn't enough — it must stay fast on large data.