SQL

Queries you can watch run — joins, groups, indexes, transactions.

1. 1SELECT BasicsName the columns you want; the table hands them back.4m
2. 2WHERE and FilteringFilter in the database, not in your application loop.4m
3. 3ORDER BY and LIMITSort once in the engine, then take only the slice you show.4m
4. 4Aggregations & GROUP BYFold many rows into one number per group.5m
5. 5INNER and OUTER JOINsMatch rows across tables — and decide who survives a miss.6m
6. 6SubqueriesA query inside a query, answered before the outer one runs.5m
7. 7IndexesA second, sorted copy of one column that ends the full scan.6m
8. 8Transactions & ACIDAll of the writes land, or none of them do.6m
9. 9Query Execution OrderSQL is written top-down but evaluated in a different order.5m
10. 10The N+1 Query ProblemOne query for the list, then one more for every single row.5m