Question

此代码对a和b进行操作，并检查结果是否等于c。如果是，只需打印此行。我的问题是如何更改此代码以显示结果（a / b）= 0时的行。

SELECT id, a, b, operation, c
FROM expressions
where
case
    when operation LIKE '+' AND (a + b = c) then c
    when operation LIKE '-' AND (a - b = c) then c 
    when operation like '/' AND (a / b = c) then c
    when operation like '*' AND (a * b = c) then c
ELSE FALSE END;

输出：

id  a   b   operation   c
1   2   3   +   5
4   4   7   *   28

11  0   1   /   0
14  239 0   *   0
15  18  18  -   0

1,2行可以打印。应该打印3,4,5行，但它们不是！当a / b = 0时，sql查询中的第二个条件为false - 不打印行，例如0/1 = 0.它为0，应该打印。与1/0相反，不应该打印。我的解决方案是将（a / b = c）转换为无符号，但它不起作用？

Answer 1

您不应混用boolean和int等类型，因为会发生隐式转换。

使用显式值代替TRUE/FALSE（0被视为FALSE）。

SELECT id, a, b, operation, c
FROM expressions
where
case
    when operation LIKE '+' AND (a + b = c) then 1
    when operation LIKE '-' AND (a - b = c) then 1 
    when operation like '/' AND (a / b = c) then 1
    when operation like '*' AND (a * b = c) then 1
ELSE 0 END = 1;

或者：

SELECT id, a, b, operation, c
FROM expressions
where
case
    when operation LIKE '+' AND (a + b = c) then TRUE
    when operation LIKE '-' AND (a - b = c) then TRUE
    when operation like '/' AND (a / b = c) then TRUE
    when operation like '*' AND (a * b = c) then TRUE
ELSE FALSE END;

Answer 2

正如已经指出的那样，问题是0被视为错误。

我会将逻辑简化为：

SELECT id, a, b, operation, c
FROM expressions
WHERE (operation LIKE '+' AND (a + b = c) ) OR
      (operation LIKE '-' AND (a - b = c) ) OR
      (operation LIKE '/' AND (a / b = c) ) OR
      (operation LIKE '*' AND (a * b = c) );

我不认为CASE使代码更容易理解。

如果您担心被零除，请使用nullif()：

      (operation LIKE '/' AND (a / nullif(b, 0) = c) ) OR

如何在mysql查询中显示零值？

2 个答案: