Question

我不是SQL专家，但我无法理解为什么我使用以下代码收到错误：http://sqlfiddle.com/#!3/2de76/7。请有人告诉我这有什么问题。感谢。

DECLARE @total INT
SET @total = 0
SELECT
    s1.RowCountID,
    CASE
        WHEN s1.dayTotal < s2.dayTotal      THEN @total = @total
        WHEN s1.dayTotal > s2.dayTotal      THEN @total = @total + (s1.dayTotal - s2.dayTotal)
    END     AS res,
    s1.dayTotal,
    s2.dayTotal
FROM simple_summary s1
JOIN simple_summary s2 ON s2.RowCountID = s1.RowCountID - 1
ORDER BY s1.RowCountID ASC

预期产出：

rowCount,res,dayTotal,dayTotal
1,3,3,0
2,4,4,3
3,4,3,4
4,7,6,3

Answer 1

您正在尝试使用CASE的THEN来改变变量的值。不是这样的。然而，这可行，并且看起来更接近您可能想要实现的目标：

DECLARE @total INT
SET @total = 0
SELECT 
    s1.RowCountID,
    CASE
        WHEN s1.dayTotal < s2.dayTotal      THEN @total
        WHEN s1.dayTotal > s2.dayTotal      THEN (s1.dayTotal - s2.dayTotal)
    END     AS res,
    s1.dayTotal,
    s2.dayTotal
FROM simple_summary s1
JOIN simple_summary s2 ON s2.RowCountID = s1.RowCountID - 1
ORDER BY s1.RowCountID ASC

PS - 您的CASE不考虑s1.dayTotal = s2.dayTotal的可能性。不确定没关系。

PPS - 如果您希望第二个WHEN总计总和与差异，请使用

WHEN s1.dayTotal > s2.dayTotal      THEN @total+(s1.dayTotal - s2.dayTotal)

PPPS - 这似乎产生了所需的结果集：

select a.RowCountID, case when b.diff > 0 then a.res+b.diff else a.res end as res, a.daytotal1, a.daytotal2  from
(
SELECT 
    s1.RowCountID,
    CASE
        WHEN s1.dayTotal < s2.dayTotal      THEN s2.dayTotal
        WHEN s1.dayTotal >= s2.dayTotal     THEN s1.dayTotal
    END     AS res,
    s1.dayTotal as dayTotal1,
    s2.dayTotal as dayTotal2,
    s2.dayTotal - s1.dayTotal as diff
FROM simple_summary s1
JOIN simple_summary s2 ON s2.RowCountID = s1.RowCountID - 1
  ) a 
  left join
(
  SELECT 
    s1.RowCountID,
    CASE
        WHEN s1.dayTotal < s2.dayTotal      THEN s2.dayTotal
        WHEN s1.dayTotal >= s2.dayTotal     THEN s1.dayTotal
    END     AS res,
    s1.dayTotal as dayTotal1,
    s2.dayTotal as dayTotal2,
    s2.dayTotal - s1.dayTotal as diff
FROM simple_summary s1
JOIN simple_summary s2 ON s2.RowCountID = s1.RowCountID - 1
) b on a.rowcountID = b.rowcountID+1
order by a.rowcountID

不确定这种自加入查询的名称是什么，但它应该有一个名称：）

希望它运作良好！

Answer 2

您需要删除＆＃34; @total =＆＃34;来自case声明。

DECLARE @total int
SET @total = 0

SELECT
  s1.RowCountID,
  CASE
    WHEN s1.dayTotal < s2.dayTotal THEN @total
    WHEN s1.dayTotal > s2.dayTotal THEN @total + (s1.dayTotal - s2.dayTotal)
  END AS res,
  s1.dayTotal,
  s2.dayTotal
FROM simple_summary s1
JOIN simple_summary s2
  ON s2.RowCountID = (s1.RowCountID - 1)
ORDER BY s1.RowCountID ASC

Answer 3

在进一步调查（并找到how to get cumulative sum）之后确定，以下是使其正常工作的正确代码（但添加了case命令）：

SELECT
    s1.RowCountID,
      SUM(
      CASE
        WHEN s1.dayTotal < s2.dayTotal      THEN 0
        WHEN s1.dayTotal > s2.dayTotal      THEN s1.dayTotal - s2.dayTotal
      END) OVER(
           ORDER BY s1.RowCountID ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
      ) AS res2,
    s1.dayTotal,
    s2.dayTotal
FROM simple_summary s1
JOIN simple_summary s2 ON s2.RowCountID = s1.RowCountID - 1
ORDER BY s1.RowCountID ASC

我的实际问题是我也使用MySQL（我正在试验看其他地方是否可能）所以接下来的问题是MySQL的外观如何？这需要进一步调查!!

SQL Server上的语法错误不正确

3 个答案: