sql server 上的按位非示例

Question

在SQL Server的网上书籍中，有一个解释bitwise not操作符的例子让我很困惑：

170（a_int_value 或 A）的二进制表示为 0000 0000 1010 1010。对该值执行按位 NOT 运算会产生二进制结果 1111 1111 0101 0101，即十进制 -171。

因为一个整数在 SQL Server 中是 4 个字节，它不应该是：

170: 0000 0000 0000 0000 0000 0000 1010 1010 (0x000000AA)

和

~170 = -171 : 1111 1111 1111 1111 1111 1111 0101 0101 (0xFFFFFF55)

例如，按位非运算符给出的结果是：1111 1111 0101 0101，即 0xFF55，如果我们将其转换为 int，则它完全是一个不同的整数：

Select cast(0xFF55 as int)
--> 65365

如果是 smallint，那么这个例子就是真的：

Select cast(0xFF55 as smallint)
--> -171

该示例是否遗漏了 1 的前 2 个字节，还是我误解了什么？

谢谢，

Answer 1

你是对的。

那个article现在已经更新为说

170（a_int_value 或A）的二进制表示为0000 0000 0000 0000 0000 0000 1010 1010。对该值执行按位非运算会产生二进制结果1111 1111 1111 1111 1111 1111 0101 0101，即十进制-171。

Answer 2

确实，如果您使用按位与 (&) 执行强制转换，给定 SQL 值中的最大 INT，则从 1 开始并向上移动，注意最大 INT 是最高值。

参考 (&) https://docs.microsoft.com/en-us/sql/t-sql/language-elements/bitwise-and-transact-sql?view=sql-server-ver15

因此，正如您所看到的，它取决于输入存储大小的类型（请参阅该 OP 引用页面上的注释），在这里我们可以看到它会是什么（我添加了空格以使其在视觉上更容易看到）注意2147483647 是最大 INT

BinaryStringNot170
---------------------------------------
1111 1111 1111 1111 1111 1111 0101 0101

BinaryString170
---------------------------------------
1000 0000 0000 0000 0000 0000 1010 1010

以及产生这些的查询：

SELECT 
     cast( cast((~ 170) & 2147483647 as bit) as CHAR(1)) 
    +cast( cast((~ 170) & 1073741824 as bit) as CHAR(1)) 
    +cast( cast((~ 170) & 536870912 as bit) as CHAR(1)) 
    +cast( cast((~ 170) & 268435456 as bit) as CHAR(1)) + ' '
    +cast( cast((~ 170) & 134217728 as bit) as CHAR(1)) 
    +cast( cast((~ 170) & 67108864 as bit) as CHAR(1)) 
    +cast( cast((~ 170) & 33554432 as bit) as CHAR(1)) 
    +cast( cast((~ 170) & 16777216 as bit) as CHAR(1)) + ' '
    +cast( cast((~ 170) & 8388608 as bit) as CHAR(1)) 
    +cast( cast((~ 170) & 4194304 as bit) as CHAR(1)) 
    +cast( cast((~ 170) & 2097152 as bit) as CHAR(1)) 
    +cast( cast((~ 170) & 1048576 as bit) as CHAR(1)) + ' '
    +cast( cast((~ 170) & 524288 as bit) as CHAR(1)) 
    +cast( cast((~ 170) & 262144 as bit) as CHAR(1)) 
    +cast( cast((~ 170) & 131072 as bit) as CHAR(1)) 
    +cast( cast((~ 170) & 65536 as bit) as CHAR(1)) + ' '
    +cast( cast((~ 170) & 32768 as bit) as CHAR(1)) 
    +cast( cast((~ 170) & 16384 as bit) as CHAR(1)) 
    +cast( cast((~ 170) & 8192 as bit) as CHAR(1)) 
    +cast( cast((~ 170) & 4096 as bit) as CHAR(1)) + ' '
    +cast( cast((~ 170) & 2048 as bit) as CHAR(1)) 
    +cast( cast((~ 170) & 1024 as bit) as CHAR(1)) 
    +cast( cast((~ 170) & 512 as bit) as CHAR(1)) 
    +cast( cast((~ 170) & 256 as bit) as CHAR(1)) + ' '
    +cast( cast((~ 170) & 128 as bit) as CHAR(1)) 
    +cast( cast((~ 170) & 64 as bit) as CHAR(1)) 
    +cast( cast((~ 170) & 32 as bit) as CHAR(1))
    +cast( cast((~ 170) & 16 as bit)  as CHAR(1)) + ' '
    +cast( cast((~ 170) & 8 as bit)  as CHAR(1))
    +cast( cast((~ 170) & 4 as bit)  as CHAR(1))
    +cast( cast((~ 170) & 2 as bit)   as CHAR(1))
    +cast( cast((~ 170) & 1 as bit)  as CHAR(1))
 AS BinaryStringNot170


 SELECT 
     cast( cast(( 170) & 2147483647 as bit) as CHAR(1))  
    +cast( cast(( 170) & 1073741824 as bit) as CHAR(1)) 
    +cast( cast(( 170) & 536870912 as bit) as CHAR(1)) 
    +cast( cast(( 170) & 268435456 as bit) as CHAR(1)) + ' '
    +cast( cast(( 170) & 134217728 as bit) as CHAR(1))  
    +cast( cast(( 170) & 67108864 as bit) as CHAR(1)) 
    +cast( cast(( 170) & 33554432 as bit) as CHAR(1)) 
    +cast( cast(( 170) & 16777216 as bit) as CHAR(1))  + ' '
    +cast( cast(( 170) & 8388608 as bit) as CHAR(1)) 
    +cast( cast(( 170) & 4194304 as bit) as CHAR(1)) 
    +cast( cast(( 170) & 2097152 as bit) as CHAR(1)) 
    +cast( cast(( 170) & 1048576 as bit) as CHAR(1))  + ' '
    +cast( cast(( 170) & 524288 as bit) as CHAR(1)) 
    +cast( cast(( 170) & 262144 as bit) as CHAR(1)) 
    +cast( cast(( 170) & 131072 as bit) as CHAR(1)) 
    +cast( cast(( 170) & 65536 as bit) as CHAR(1)) + ' '
    +cast( cast(( 170) & 32768 as bit) as CHAR(1)) 
    +cast( cast(( 170) & 16384 as bit) as CHAR(1))  
    +cast( cast(( 170) & 8192 as bit) as CHAR(1)) 
    +cast( cast(( 170) & 4096 as bit) as CHAR(1)) + ' '
    +cast( cast(( 170) & 2048 as bit) as CHAR(1))  
    +cast( cast(( 170) & 1024 as bit) as CHAR(1)) 
    +cast( cast(( 170) & 512 as bit) as CHAR(1)) 
    +cast( cast(( 170) & 256 as bit) as CHAR(1))  + ' '
    +cast( cast(( 170) & 128 as bit) as CHAR(1)) 
    +cast( cast(( 170) & 64 as bit) as CHAR(1)) 
    +cast( cast(( 170) & 32 as bit) as CHAR(1))
    +cast( cast(( 170) & 16 as bit)  as CHAR(1)) + ' '
    +cast( cast(( 170) & 8 as bit)  as CHAR(1))
    +cast( cast(( 170) & 4 as bit)  as CHAR(1))
    +cast( cast(( 170) & 2 as bit)   as CHAR(1))
    +cast( cast(( 170) & 1 as bit)  as CHAR(1))
 AS BinaryString170

为了更完整，请注意这将返回存储在 sql 中的 MAXINT 值

SELECT CONVERT(INT, CONVERT(VARBINARY, '0x7FFFFFFF', 1))

这将返回 -1

SELECT CONVERT(INT, CONVERT(VARBINARY, '0xFFFFFFFF', 1))