MySQL Tutorial with Examples.

MySQL EXPLAIN: Reading a Full Table Scan Before You Fix It

A filtered query against 5,000 rows with no index scans every single row — EXPLAIN and EXPLAIN ANALYZE show exactly that, in real numbers, before an index changes the plan entirely.

Intermediate

For developers with core concepts down

6 lessons

Composite Indexes: The Filesort a Single-Column Index Can't Avoid

Filtering by genre and sorting by year: a single-column index still needs a manual sort afterward (2.87ms). A composite index on both columns delivers pre-sorted results — measured 21x faster, and the Sort step vanishes from the plan entirely.

A Missing Join Condition Turns 4,000 Rows Into 8 Million

Forgetting the join condition on an old-style comma join doesn't error — it silently produces a cartesian product, 8,000,000 rows where 4,000 were expected. EXPLAIN's join buffer (hash join) with no ON clause is the tell.

Isolation Levels: The Same Transaction Reading Two Different Values

Under MySQL's default REPEATABLE READ, a transaction reads the same value twice even after another session commits a change in between. Switch to READ COMMITTED and the second read sees the new value — a real, measured non-repeatable read.

A Real Deadlock: Error 1213, and the Lock-Order Fix

Two sessions locking the same two rows in opposite order produce a genuine ERROR 1213 deadlock, not a hang — MySQL detects it and kills one transaction immediately. Locking in a consistent order eliminates it entirely, replaced by an ordinary wait.

Stored Procedures and Triggers: Code That Runs Without Being Asked

A stored procedure enforces a business rule with a real SIGNAL error, and a trigger logs every stock change automatically — even for updates that never call the procedure at all.

Backup and Recovery: What a Restore Actually Gives Back

A real mysqldump, a real DELETE with no WHERE clause, and a real restore — which undoes the mistake but also erases legitimate work done after the backup, exposing exactly what a full logical restore can't do alone.

Advanced

Production-grade patterns for experienced engineers

1 lesson

mysql advanced

Replication: A Second Server, and the read_only Gap Nobody Mentions

A real primary-replica setup, checked with SHOW REPLICA STATUS instead of assumed — plus a genuine surprise: read_only alone does not stop root from writing to a replica.

Also part of MySQL

Taught in other topics. Each link opens the lesson in its home topic.

1 lesson

sql intermediate

One Script, Four Engines: Where SQL Dialects Disagree

One SQL script run on PostgreSQL, MySQL, SQL Server and SQLite: division, case, NULL order, ||, LIMIT vs TOP vs FETCH FIRST, and GROUP BY rules.