麻烦添加子查询

Question

这是合约。

我有两张表，每小时费率和单位费率由phase_no数字表示。在一张桌子上它可能有第2,3,14和81阶段，在另一张桌子上有2,14,20,83我需要将表1 sum（）添加到表2中，但是如果你看下面的结果，你会看到虽然我打电话给coalese它仍然产生NULL，你不能应用数学。希望你能看到我得到的东西。

SELECT ru.phase_no,
        ROUND(SUM(ru.units * ru.rate) * 0.75, 2) , (SELECT 
                    ROUND(SUM(rh.hours * rhh.rate) * 0.75, 2)
                FROM
                    rates_hourly_required rh
                        JOIN
                    rates_hourly rhh ON rhh.id = rh.rates_hourly_id
                WHERE
                    rh.project_id = ru.project_id and rh.phase_no =ru.phase_no group by rh.phase_no,rh.project_id)
    FROM
        rates_unit_required ru
    WHERE
        ru.project_id = 67320
    group by ru.project_id, ru.phase_no

也许有更好的方法来处理此查询。

Answer 1

使用LEFT JOIN而不是相关的子查询

SELECT ru.phase_no, 
    ROUND(SUM(ru.units * ru.rate) * 0.75, 2) AS ru_total,
    IFNULL(rh_total, 0) AS rh_total
FROM rates_unit_required AS ru
LEFT JOIN (
    SELECT rh.phase_no, ROUND(SUM(rh.hours * rhh.rate) * 0.75, 2) AS rh_total
    FROM rates_hourly_required rh
    JOIN rates_hourly rhh ON rhh.id = rh.rates_hourly_id
    WHERE rh.project_id = 67320
    GROUP BY rh.phase_no
) AS rh ON rh.project_id = ru.project_id AND rh.phase_no = ru.phase_no
WHERE ru.project_id = 67320
GROUP BY ru.phase_no

project_id当您在WHERE子句中选择特定值时，"a": "str"分组也毫无意义。