httk.store.backend.postgresql.compiler

PostgreSQL-specific SQLAlchemy dialect compilation hooks.

The rest of httk.store.backend.sql deals in generic SQLAlchemy objects. This module is the adapter boundary that rewrites the httk_fraction_scaled_equal call into inline SQL for the PostgreSQL dialect, because PostgreSQL cannot host the per-connection Python scalar function that SQLite and DuckDB register.

Fractions are persisted as canonical "p/q" text (reduced, positive denominator), but the caller also passes integer-form factors (for example a constant 1/2 supplied as separate value and factor) that carry no /q part; those take an implicit denominator of 1. Exact rational equality is therefore evaluated by casting each argument to text, splitting into numerator and denominator, and cross-multiplying with PostgreSQL’s arbitrary-precision numeric type – so, unlike ClickHouse’s bounded Int256 inline, no digit budget or zero-denominator guard is needed. The only theoretical bound is numeric’s ~131072-integer-digit cap, the same practical ceiling ClickHouse’s Int256 inline already accepts; no runtime guard is warranted.