Macro sql 

macro_rules! sql {
    ($query:expr) => { ... };
}

Convert SQL with ? placeholders to the active backend’s placeholder style.

SQLite: returns the input &str directly — zero allocation, zero runtime cost.

PostgreSQL: rewrites ? to $1, $2, … and ?N (SQLite’s numbered placeholder, e.g. ?1) to $N using rewrite_placeholders. Repeated references to the same ?N collapse to the same $N. The rewrite runs at most once per call site: the result is memoized in a call-site-local LazyLock<String>, so a query executed in a loop or on a hot path incurs the rewrite cost once per process lifetime rather than once per execution. This requires $query to be a compile-time-constant expression (in practice, always a string literal at every call site in this workspace) — the closure passed to LazyLock::new captures $query and runs exactly once, so a runtime-varying $query would silently freeze at its first-seen value. Do NOT wrap PostgreSQL JSONB queries using ?/?|/?& operators through this macro; use $N placeholders directly for those.

Example

let rows = sqlx::query(sql!("SELECT id FROM messages WHERE conversation_id = ?"))
    .bind(cid)
    .fetch_all(&pool)
    .await?;