sql-programming - SKILL.md Agent Skill

name: sql-programming description: General SQL programming, formatting, debugging, and query-shaping tips. Use for SQL work that is not specifically about PostGIS spatial data.

Make sure every create statement or CTE has a descriptive comment -- in front of it.
Write enough comments so you can deduce what was a requirement in the future and not walk in circles.
Every feature needs to have comprehensive up-to-date documentation near it.

SQL is lowercase unless instructed otherwise.
Values in databases and layers should be absolute as much as possible: store "birthday" or "construction date" instead of "age".
Do not mix tabs and spaces in code.
Add empty lines between logical blocks.
Format the code nicely and consistently.

Consider BRIN indexes for very large naturally ordered tables that will be used for ad-hoc range queries.
If you have a cache table that has a primary key, it can make sense to add frequently read values into including on the same index for faster lookup.

Make sure error messages towards developers are better than just "500 Internal Server Error".
Don't stub stuff out with insane fallbacks like lat = 0 and lon = 0; instead make the rest of the code work around data absence and inform the user.
SQL files should be idempotent: drop table if exists + create table as; add comments to make queries faster to grasp.
Create both "up" and "down/rollback" migrations when the project expects reversible migrations.
Don't run one SQL file from another SQL file - this quickly becomes a mess with relative file paths.

sum(case when A then 1 else 0 end) is just count() filter (where A).
row_number() ... = 1 can likely be redone as order by + limit 1 (possibly with distinct on or lateral).
exists(select 1 from ...) is just exists(select from ...).
tags ->> 'key' = 'value' is just tags @> '{"key": "value"}' - works faster with indexes.
You can't create an ordered table and then rely on it to be ordered on scan without order by.