如何在 MySQL 中创建累积和列？

要在MySQL中创建累积和列，您需要创建一个变量并将值设置为0。累积和会以当前值逐步递增下一个值。

首先，您需要在 SET 的帮助下创建一个变量。语法如下 -

set @anyVariableName:= 0;

在 MySQL 中创建累积和列的语法如下 -

select yourColumnName1,yourColumnName2,........N,(@anyVariableName := @anyVariableName + yourColumnName2) as anyVariableName
from yourTableName order by yourColumnName1;

为了理解上述概念，让我们创建一个表。以下是创建表的查询 -

mysql> create table CumulativeSumDemo
   −> (
   −> BookId int,
   −> BookPrice int
   −> );
Query OK, 0 rows affected (0.67 sec)

借助select语句向表中插入一些记录。插入记录的查询如下 -

mysql> insert into CumulativeSumDemo values(101,400);
Query OK, 1 row affected (0.15 sec)

mysql> insert into CumulativeSumDemo values(102,500);
Query OK, 1 row affected (0.16 sec)

mysql> insert into CumulativeSumDemo values(103,600);
Query OK, 1 row affected (0.16 sec)

mysql> insert into CumulativeSumDemo values(104,1000);
Query OK, 1 row affected (0.18 sec)

显示我借助插入命令插入的所有记录。查询如下 -

mysql> select *from CumulativeSumDemo;

以下是输出 -

+--------+-----------+
| BookId | BookPrice |
+--------+-----------+
|    101 |       400 |
|    102 |       500 |
|    103 |       600 |
|    104 |      1000 |
+--------+-----------+
4 rows in set (0.00 sec)

要添加累积和列，首先需要创建一个变量。查询如下 -

mysql> set @CumulativeSum := 0;
Query OK, 0 rows affected (0.00 sec)

实现开头讨论的上述语法来添加累积和列。查询如下 -

mysql> select BookId,BookPrice,(@CumulativeSum := @CumulativeSum + BookPrice) as CumSum
   −> from CumulativeSumDemo order by BookId;

以下是输出。这里累积总和列也可见 -

+--------+-----------+--------+
| BookId | BookPrice | CumSum |
+--------+-----------+--------+
|    101 |       400 |    400 |
|    102 |       500 |    900 |
|    103 |       600 |   1500 |
|    104 |      1000 |   2500 |
+--------+-----------+--------+
4 rows in set (0.00 sec)

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