关于后端:MySQL实现累加累乘累减累除

MySQL 实现累加、累乘、累减、累除

table: TEST
+-----------+---------+---------+
| PARENT_ID | PART_ID | QUALITY |
+-----------+---------+---------+
|         1 |       1 |       2 |
|         1 |       2 |       3 |
|         1 |       3 |       2 |
|         1 |       4 |       5 |
|         2 |       2 |       3 |
|         2 |       3 |       5 |
|         2 |       4 |       7 |
+-----------+---------+---------+

累加

最简略，用 sum+over 即可

SELECT
    T.*,
    SUM(T.QUALITY) OVER (PARTITION BY T.PARENT_ID ORDER BY T.PART_ID) RUNNING_QUALITY
FROM
    TEST T;

累乘

应用 EXP(SUM(LN(字段)) 实现累乘，其余的和累加一样！

SELECT
    T.*,
    ROUND(EXP(SUM(LN(T.QUALITY)) OVER(PARTITION BY T.PARENT_ID ORDER BY T.PART_ID)),0) RUNNING_PROD
FROM
    TEST T;

累减

累减巧用负号！

（1）先用 row_number 排序

SELECT
  T.*,
  ROW_NUMBER() OVER(PARTITION BY T.PARENT_ID ORDER BY T.PART_ID) RN
FROM TEST T

+-----------+---------+---------+----+
| PARENT_ID | PART_ID | QUALITY | RN |
+-----------+---------+---------+----+
|         1 |       1 |       2 |  1 |
|         1 |       2 |       3 |  2 |
|         1 |       3 |       2 |  3 |
|         1 |       4 |       5 |  4 |
|         2 |       2 |       3 |  1 |
|         2 |       3 |       5 |  2 |
|         2 |       4 |       7 |  3 |
+-----------+---------+---------+----+

（2）当 RN= 1 时，保留第一位的数字，其余的全副取负号，这样就能够实现累减了！

SELECT
    T.PARENT_ID,
    T.PART_ID,
    T.QUALITY,
    SUM(if(T.RN=1,T.QUALITY,-T.QUALITY)) OVER(PARTITION BY T.PARENT_ID ORDER BY T.PART_ID) RUNNING_PROD
FROM
    (
        SELECT
            T.*,
            ROW_NUMBER() OVER(PARTITION BY T.PARENT_ID ORDER BY T.PART_ID) RN
        FROM
            TEST T) T;

累除

和累减相似，只不过这里要把非第一位的数字，取对数后再取负号，这样通过 sum 和 exp 就相当于做除法啦！

SELECT
    T.PARENT_ID,
    T.PART_ID,
    T.QUALITY,
    round(EXP(SUM(if(RN=1,LN(T.QUALITY),-LN(T.QUALITY))) OVER(PARTITION BY T.PARENT_ID ORDER BY T.PART_ID)),2) RUNNING_PROD
FROM
    (
        SELECT
            T.*,
            ROW_NUMBER() OVER(PARTITION BY T.PARENT_ID ORDER BY T.PART_ID) RN
        FROM
            TEST T)T;

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