mysql - 将 'with' 查询转换为 mysql 查询

Question

如何在 MySQL 中重写这个“with”查询？

WITH current_employees AS (
         SELECT DISTINCT emp_id
         FROM appointment
         WHERE end_date IS NULL
     ),
     appointments_2015 AS (
         SELECT a.emp_id, salary,
             CASE WHEN start_date < ’2015-01-01’ THEN ’2015-01-01’ ELSE start_date END AS start_date,
             CASE WHEN end_date < ’2016-01-01’ THEN end_date ELSE ’2015-12-31’ END AS end_date
         FROM appointment a
             JOIN current_employees ce ON a.emp_id = ce.emp_id
         WHERE start_date < ’2016-01-01’ AND (end_date >= ’2015-01-01’ OR end_date IS NULL)
     )
     SELECT
         emp_id,
         SUM( salary * (DATEDIFF(end_date, start_date) + 1) / 365 ) AS total
     FROM appointments_2015
     GROUP BY emp_id

Answer 1

您需要将 current_employees 和 appointments_2015 的用法替换为其定义:

SELECT
    emp_id,
    SUM( salary * (DATEDIFF(end_date, start_date) + 1) / 365 ) AS total
FROM (
    -- replacement code for appointments_2015
    SELECT a.emp_id, salary,
        CASE WHEN start_date < ’2015-01-01’ THEN ’2015-01-01’ ELSE start_date END AS start_date,
        CASE WHEN end_date < ’2016-01-01’ THEN end_date ELSE ’2015-12-31’ END AS end_date
    FROM appointment a
        JOIN ( 
            -- replacement code for current_employees
            SELECT DISTINCT emp_id
            FROM appointment
            WHERE end_date IS NULL
        ) ce ON a.emp_id = ce.emp_id
    WHERE start_date < ’2016-01-01’ AND (end_date >= ’2015-01-01’ OR end_date IS NULL)
) appointments_2015
GROUP BY emp_id