Constant CHECK_FOREIGN_KEY_SQL 

const CHECK_FOREIGN_KEY_SQL: &str = r#"
    SELECT EXISTS (
        SELECT 1
        FROM pg_constraint c
        JOIN pg_class t ON t.oid = c.conrelid
        JOIN pg_namespace n ON n.oid = t.relnamespace
        WHERE n.nspname = $1
          AND t.relname = $2
          AND c.contype = 'f'
    )
"#;