意外的SQL除法结果？

我使用SQL Server

通过与部门合作，我在这两个查询中收集了我的发现，您可以使用SQL Server版本重现这两个查询

我希望在这两种情况下，带整数的除法都有相同的值。 因为不管我的表中的值如何，如果我得到意外的结果，我最终会遇到一个逻辑错误，有时很难调查

sqla:

WITH s AS (
    SELECT 'Integer' AS c, 1 AS k UNION
    SELECT 'Float', 1 UNION
    SELECT 'NULL', NULL
) 
SELECT 
    c AS [Type],
    k/10 AS                          'Division',
    CAST(k as numeric(38,4))/10 AS 'Cast',
    COALESCE(k, 0)/10           AS 'Coalesce',
    COALESCE(k, .0)/10          AS 'Coalesce with float'
FROM s; 

WITH s AS (
    SELECT 'Integer' AS c, 1 AS k UNION
    SELECT 'Float', .1 UNION
    SELECT 'NULL', NULL
) 
SELECT 
    c AS [Type],
    k/10 AS                          'Division',
    CAST(k as numeric(38,4))/10 AS 'Cast',
    COALESCE(k, 0)/10           AS 'Coalesce',
    COALESCE(k, .0)/10          AS 'Coalesce with float'
FROM s; 

结果A

Type        Division    Cast        Coalesce    Coalesce with float
Float       0           0.100000    0           0.100000
Integer     0           0.100000    0           0.100000
NULL        NULL        NULL        0           0.000000

Type        Division    Cast        Coalesce    Coalesce with float
Float       0.010000    0.010000    0.010000    0.010000
Integer     0.100000    0.100000    0.100000    0.100000
NULL        NULL        NULL        0.000000    0.000000

WITH s AS (
    SELECT 'Integer' AS c, 1 AS k UNION
    SELECT 'Float', 1 UNION
    SELECT 'NULL', NULL
) 
SELECT c AS [Type],
       FLOOR(k/10) AS 'Division',
       CAST(k as numeric(38,4))/10 AS 'Cast',
       FLOOR(COALESCE(k, 0)/10) AS 'Coalesce',
       COALESCE(k, .0)/10 AS 'Coalesce with float'
FROM s; 

SQL B:

WITH s AS (
    SELECT 'Integer' AS c, 1 AS k UNION
    SELECT 'Float', 1 UNION
    SELECT 'NULL', NULL
) 
SELECT 
    c AS [Type],
    k/10 AS                          'Division',
    CAST(k as numeric(38,4))/10 AS 'Cast',
    COALESCE(k, 0)/10           AS 'Coalesce',
    COALESCE(k, .0)/10          AS 'Coalesce with float'
FROM s; 

WITH s AS (
    SELECT 'Integer' AS c, 1 AS k UNION
    SELECT 'Float', .1 UNION
    SELECT 'NULL', NULL
) 
SELECT 
    c AS [Type],
    k/10 AS                          'Division',
    CAST(k as numeric(38,4))/10 AS 'Cast',
    COALESCE(k, 0)/10           AS 'Coalesce',
    COALESCE(k, .0)/10          AS 'Coalesce with float'
FROM s; 

结果A

Type        Division    Cast        Coalesce    Coalesce with float
Float       0           0.100000    0           0.100000
Integer     0           0.100000    0           0.100000
NULL        NULL        NULL        0           0.000000

Type        Division    Cast        Coalesce    Coalesce with float
Float       0.010000    0.010000    0.010000    0.010000
Integer     0.100000    0.100000    0.100000    0.100000
NULL        NULL        NULL        0.000000    0.000000

WITH s AS (
    SELECT 'Integer' AS c, 1 AS k UNION
    SELECT 'Float', 1 UNION
    SELECT 'NULL', NULL
) 
SELECT c AS [Type],
       FLOOR(k/10) AS 'Division',
       CAST(k as numeric(38,4))/10 AS 'Cast',
       FLOOR(COALESCE(k, 0)/10) AS 'Coalesce',
       COALESCE(k, .0)/10 AS 'Coalesce with float'
FROM s; 

---

您的第一个表是所有整数

选择“Float”，1是一个INT

不是一个Float，仅仅因为你把单词放在那里。它将被暗示为INT，因为没有小数点

然后，你知道整数除法使用整数。。。例如

select 3/10

是0，而不是用

select 3/10.0

得到的.3000。如果希望返回十进制/浮点，则分子或分母必须是浮点（或两者都是）

编辑

在你最后的评论之后，我更加理解你的问题。当您将不同的数据类型合并在一起时（您在第二个

CTE

中执行了此操作），SQL Server将隐式地将它们转换为必要的数据类型，以伴随所有输入

所以，如果你从cte中选择*。。。您将看到您的1已转换为1.0。一个列只能有一个数据类型。在本例中，SQL Server必须选择

INT

或

FLOAT

。如果选择INT，则会出现数据完整性问题

WITH s AS (
    SELECT 'Integer' AS c, 1 AS k UNION
    SELECT 'Float', .1 UNION
    SELECT 'NULL', NULL
) 

select * from s

---

如果希望这两个数据集的结果相同，请使用FLOOR（）函数

SQL A

Type        Division    Cast        Coalesce    Coalesce with float
Float       0           0.100000    0           0.100000
Integer     0           0.100000    0           0.100000
NULL        NULL        NULL        0           0.000000

Type        Division    Cast        Coalesce    Coalesce with float
Float       0.010000    0.010000    0.010000    0.010000
Integer     0.100000    0.100000    0.100000    0.100000
NULL        NULL        NULL        0.000000    0.000000

WITH s AS (
    SELECT 'Integer' AS c, 1 AS k UNION
    SELECT 'Float', 1 UNION
    SELECT 'NULL', NULL
) 
SELECT c AS [Type],
       FLOOR(k/10) AS 'Division',
       CAST(k as numeric(38,4))/10 AS 'Cast',
       FLOOR(COALESCE(k, 0)/10) AS 'Coalesce',
       COALESCE(k, .0)/10 AS 'Coalesce with float'
FROM s; 

SQL B

WITH s AS (
    SELECT 'Integer' AS c, 1 AS k UNION
    SELECT 'Float', .1 UNION
    SELECT 'NULL', NULL
) 
SELECT 
    c AS [Type],
    FLOOR(k/10) AS 'Division',
    CAST(k as numeric(38,4))/10 AS 'Cast',
    FLOOR(COALESCE(k, 0)/10) AS 'Coalesce',
    COALESCE(FLOOR(k), .0)/10 AS 'Coalesce with float'
FROM s; 

两个查询的结果

Type    Division    Cast        Coalesce    Coalesce with float
Float   0           0.100000    0           0.100000
Integer 0           0.100000    0           0.100000
NULL    NULL        NULL        0           0.000000

---

请检查第二条语句，选择“Float”。1@profimedica在第二条语句中，有一个小数点。与0.1相同。这在第一个例子中是不存在的，这就是整数除法返回整数的原因。我必须强调的是，我创建这两个场景时要注意添加点以创建浮点的效果。另外，我希望整数除法的结果是一个整数，浮点运算的结果是一个浮点运算。这是两个示例中第一行的情况。意外的结果出现在整数行上，其中参与者相同，但输出类型由浮点结果决定。在SQL B中，floor结果是一个整数，由oalesce:COALESCE（floor（k），.0）转换回浮点。实际上，您的方法将强制结果的类型，scsimon解释说，类型优先级tah是为整个列决定的。