Question

我有以下查询

SELECT date, t1.col1, t2.col2, t1.col1 * t2.col2 AS `col3`
FROM t1
INNER JOIN t2 ON t2.col3 = t1.col3
WHERE t2.col3 = 2
ORDER BY date ASC

现在我想要添加一个累积总和为col3的列，所以按照这个问题（Create a Cumulative Sum Column in MySQL）我想出了这个：

SET @csum := 0;
SELECT date, t1.col1, t2.col2, t1.col1 * t2.col2 AS `col3`, (@csum := @csum + `col3`) AS `sum`
FROM t1
INNER JOIN t2 ON t2.col3 = t1.col3
WHERE t2.col3 = 2
ORDER BY date ASC

但由于col3也是在查询中生成的，因此它显然无法正常工作。如何更改它以使生成的列可以有累积总和？

Answer 1

您可以在col3 - 表达式中使用与@csum相同的公式，也可以使用周围的select语句添加sum - 列。

所以要么......

SET @csum := 0;
SELECT date, t1.col1, t2.col2, t1.col1 * t2.col2 AS `col3`, (@csum := @csum + (t1.col1 * t2.col2)) AS `sum`
FROM t1
INNER JOIN t2 ON t2.col3 = t1.col3
WHERE t2.col3 = 2
ORDER BY date ASC

或......

SET @csum := 0;
SELECT ti.*, (@csum := @csum + ti.col3) AS `sum`
FROM (
  SELECT date, t1.col1, t2.col2, t1.col1 * t2.col2 AS `col3`, 
  FROM t1
  INNER JOIN t2 ON t2.col3 = t1.col3
  WHERE t2.col3 = 2
  ORDER BY date ASC) ti

Answer 2

SET @csum := 0;

SELECT
    date, t1.col1, t2.col2,
    @tmp := t1.col1 * t2.col2 AS `col3`,
    @csum := @csum + @tmp AS `sum`
FROM t1
INNER JOIN t2 ON t2.col3 = t1.col3
WHERE t2.col3 = 2
ORDER BY date ASC

OR

SELECT
date, t1.col1, t2.col2,
@tmp := t1.col1 * t2.col2 AS `col3`,
@csum := IFNULL(@csum, 0) + @tmp AS `sum`
FROM t1
INNER JOIN t2 ON t2.col3 = t1.col3
WHERE t2.col3 = 2
ORDER BY date ASC

Answer 3

虽然@StephanLechners在直接使用MySQL数据库（使用phpmyadmin等工具）时可以解答，但在我的情况下，在将我的查询添加到我的PHP代码时，它无效。所以万一有人遇到类似的问题，这里的查询对我有用。

我正在使用WordPress，所以使用$wpdb->get_results来执行查询。这可能是Stephans查询对我不起作用的原因之一。

所以有效的查询如下。

SELECT t.date, t.col1, t.col2, t.sum, @runtot:=@runtot + t.sum AS cumulativesum
FROM (SELECT date, t1.col1, t2.col2, t2.col2 * col1 AS `sum` 
FROM t1
INNER JOIN t2 ON t1.col3 = t2.col3
WHERE t2.id = 2) t 
JOIN (SELECT @runtot := 0 AS dummy) dummy 
ORDER BY date

从生成的列创建一个mysql累积和列

3 个答案: