Convert Oracle PL/SQL to modern cloud SQL

-- Organisational rollup with CONNECT BY
SELECT  employee_id,
        manager_id,
        LEVEL                                   AS depth,
        SYS_CONNECT_BY_PATH(employee_name, '/') AS org_path,
        CONNECT_BY_ROOT employee_name           AS top_manager,
        CONNECT_BY_ISLEAF                       AS is_leaf
FROM    employees
START WITH manager_id IS NULL
CONNECT BY PRIOR employee_id = manager_id
ORDER SIBLINGS BY employee_name;

-- CONNECT BY → recursive CTE
WITH RECURSIVE org AS (
    -- START WITH
    SELECT  employee_id, manager_id, employee_name,
            1                              AS depth,
            '/' || employee_name           AS org_path,
            employee_name                  AS top_manager
    FROM    employees
    WHERE   manager_id IS NULL

    UNION ALL

    -- CONNECT BY PRIOR employee_id = manager_id
    SELECT  e.employee_id, e.manager_id, e.employee_name,
            o.depth + 1,
            o.org_path || '/' || e.employee_name,
            o.top_manager
    FROM    employees e
    JOIN    org o ON e.manager_id = o.employee_id
)
SELECT  o.*,
        -- CONNECT_BY_ISLEAF
        CASE WHEN NOT EXISTS (
                 SELECT 1 FROM employees c
                 WHERE c.manager_id = o.employee_id)
             THEN 1 ELSE 0 END AS is_leaf
FROM    org o
ORDER BY org_path;