contexture: Instructions file for GitHub Copilot

sql rules

Auto-loaded by Copilot when editing files matching **/*.sql. Generated from architectural-rules/sql/ — do not hand-edit.

SQL formatting

Reserved keywords in UPPERCASE (SELECT, FROM, WHERE, JOIN); identifiers in lower_snake_case. The case split makes structure scannable at a glance. Right-align root keywords to a "river" so clause bodies start at a common column. Keeps multi-clause queries readable as a block. One column per line in long SELECT lists; one condition per line in multi-predicate WHERE/ON. Diffs then show exactly what changed. Alias tables with meaningful short names, not single letters where it hurts readability. Always qualify columns in multi-table queries (o.total, not bare total).

Why: SQL is read far more than written and lives in diffs forever; consistent layout turns a 40-line query from a wall into a structure. Source: SQL Style Guide (sqlstyle.guide / Holywell).

SQL query structure

Name columns explicitly; never SELECT * in application/view code. * breaks silently when the schema changes and ships columns you don't need over the wire. Use explicit JOIN ... ON syntax, never comma-joins with join conditions in WHERE. The join intent and the filter intent stay separated and visible. Prefer CTEs (WITH) over deeply nested subqueries. Each step gets a name and reads top-to-bottom instead of inside-out. Keep predicates sargable — don't wrap an indexed column in a function on the filtered side (WHERE date(ts) = ... defeats the index). Filter on the raw column against a computed bound.

Why: SELECT * and function-wrapped predicates are the two query-structure choices that pass tests and then degrade or break in production as schema and data grow. Source: SQL Style Guide.

SQL schema and DDL

Pick one table-naming convention (singular customer or plural customers) and hold it across the whole schema. Columns in lower_snake_case. Primary key id; foreign keys <referenced_table>_id. Name every constraint explicitly (pk_, fk_, uq_, chk_ prefixes). Auto-generated constraint names are unreadable in errors and undroppable by name. Declare NOT NULL explicitly wherever a value is required. Default-nullable columns are a silent invitation to bad data. Choose surrogate vs natural keys deliberately and document why. Don't reach for an auto-increment id reflexively when a real unique key exists, nor use a mutable natural key as the PK. Never use reserved words (order, user, select) as identifiers — the quoting it forces everywhere is a permanent tax.