sql – Page 2 – Türker Yıldırım

The foreign key that documented an assumption

NoteJanuary 7, 20251 min read

A constraint added not for integrity, which was already sound, but because the relationship was undocumented anywhere else. A schema is the most-read document in an application and…

MySQL 8.4, and the defaults that changed underneath us

Deep diveApril 10, 202410 min read

The first long-term-support release under the new model, and an application that could not authenticate after a container image bump.

A soft delete that broke a unique index

NoteNovember 14, 20232 min read

A unique index on email, and a soft delete that leaves the row in place, which means an address can never be reused. The generated column is null…

The unique index we could not add, and the duplicates we had to find first

Deep diveNovember 7, 202310 min read

A constraint that should have existed since 2016, and 1,240 rows that violate it. Support merging customer records by hand, monthly.

A value object library, and the day it needed a serializer

Deep diveSeptember 20, 202310 min read

A Money type, an Email type, and thirty more, none of which can cross a boundary without being unwrapped by hand.

An outbox, and the publisher we removed from the transaction

Deep diveSeptember 20, 202310 min read

An order committed and an event never published, twice in one week. A broker call inside a database transaction, and a rollback after it.

A JSON column that had become a schema

Deep diveSeptember 20, 20239 min read

A settings column with forty keys, four of which are queried, and a WHERE on a JSON path scanning two million rows.

An event log that is not an event store

Deep diveAugust 10, 202310 min read

Wanting to know what happened to an order without adopting event sourcing. A support question that takes twenty minutes and three tables.

Partitioning by month, and the query that scanned all of them

Deep diveJune 27, 202310 min read

A 400 million row events table and a delete that could not finish. Dropping a partition takes two seconds; getting there takes a schema change.

Descending indexes, which finally do something

NoteMay 25, 20232 min read

The DESC keyword in an index definition was parsed and ignored until 8.0, so mixed-direction sorts always needed a filesort. This only matters for mixed directions — a…