mysql - 错误结果 mysql 仅在函数中

Question

我有以下功能，mysql查询:

BEGIN
DECLARE r float(10,2);
DECLARE var_total float(10,2);
DECLARE var_discount float(10,2) DEFAULT null;


SELECT 
    sum(x.amount)
    FROM
(
    (SELECT
        student_booking_school_course_price as amount
     FROM
        tbl_student_booking_school_course
     WHERE
        student_booking_id=par_student_booking_id
     )
    UNION
    (SELECT
        student_booking_school_accommodation_price as amount
     FROM
        tbl_student_booking_school_accommodation
     WHERE
        student_booking_id=par_student_booking_id
     )
    UNION
    (SELECT
        student_booking_school_insurance_price as amount
     FROM
        tbl_student_booking_school_insurance
     WHERE
        student_booking_id=par_student_booking_id
     )
    UNION
    (SELECT
        student_booking_school_transfer_price as amount
     FROM
        tbl_student_booking_school_transfer
     WHERE
        student_booking_id=par_student_booking_id
     )
) x

INTO var_total;

IF var_total IS NULL THEN
    SET r = 0;
END IF;

-- discount 
SET var_discount = (SELECT
    sb.student_booking_discount_amount
FROM
    tbl_student_booking sb
WHERE
    sb.student_booking_id=par_student_booking_id LIMIT 1);

IF var_discount IS NOT NULL THEN
   SET r = var_total - var_discount;
end if;


return r;

END

这些值为: 9698.88类(class) 559.55 住宿 559.55 保险 145.98 折扣

函数内的第一个查询似乎只对不同的值求和，因为折扣的结果是:10112.45，所以不是对 559.55 的一个值求和，我尝试将不同的东西输出为与字符串连接，但只看到结果是9698.88类(class)，559.55住宿等等，还可以。所以我认为问题是如果值相等则不会求和。奇怪的是，从控制台运行这个，只有函数外部的查询，结果就ok了。

我的问题是这是 MySql 的正常行为吗？如果是这样，有办法防止这种情况吗？这是一个错误吗？

Answer 1

这里您需要的是UNION ALL子句:

SELECT 
sum(x.amount)
FROM
(
(SELECT
    student_booking_school_course_price as amount
 FROM
    tbl_student_booking_school_course
 WHERE
    student_booking_id=par_student_booking_id
 )
UNION ALL
(SELECT
    student_booking_school_accommodation_price as amount
 FROM
    tbl_student_booking_school_accommodation
 WHERE
    student_booking_id=par_student_booking_id
 )
UNION ALL
(SELECT
    student_booking_school_insurance_price as amount
 FROM
    tbl_student_booking_school_insurance
 WHERE
    student_booking_id=par_student_booking_id
 )
UNION ALL
(SELECT
    student_booking_school_transfer_price as amount
 FROM
    tbl_student_booking_school_transfer
 WHERE
    student_booking_id=par_student_booking_id
 )
) x

INTO var_total;

MySQL UNION文档说:

A DISTINCT union can be produced explicitly by using UNION DISTINCT or implicitly by using UNION with no following DISTINCT or ALL keyword.