SQL Server CheckSum 是否计算 CRC?如果不是，我怎样才能让 MS SQL 计算任意 varchar 列上的 CRC? [英] Does SQL Server CheckSum calculate a CRC? If not how can I get MS SQL to calculate a CRC on an arbitrary varchar column?

问题描述

SQL Server CheckSum 是否计算 CRC?如果不是，我怎样才能让 SQL Server 在任意 varchar 列上计算 CRC?

Does SQL Server CheckSum calculate a CRC? If not how can I get SQL Server to calculate a CRC on an arbitrary varchar column?

推荐答案

我为模型的粗鲁道歉，但这似乎做了正确的 CRC32 计算.我不是 TSQL 专家，我相信真正的 SQL Server 专家可以大大改善这一点...

I apologize for the crudity of the model, but this seems to do a correct CRC32 calculation. I'm not a TSQL expert, and I'm sure that this could be improved mightily by a real SQL Server pro...

@input 是用于计算 CRC32 的变量.将其打包为 sproc 或 udf 应该很简单，并且可以将查找表分解为永久表(甚至可以动态计算).

@input is the variable to calculate the CRC32 on. It should be trivial to package this as a sproc or a udf, and the lookup table could be factored out to a permanent table (or even calculated on the fly).

无论如何，它似乎有效.我很想看到任何改进，因为学习新技巧总是好的:)

Anyway, it seems to work. I'd be interested to see any improvements, as it's always good to learn new tricks :)

我已经根据 http://crc32-checksum.waraxe.us/核对了结果a> 目前看来还不错.

I have checked my results against http://crc32-checksum.waraxe.us/ and it seems good so far.

安德鲁

DECLARE @input VARCHAR(50)
SET @input = 'test'

SET NOCOUNT ON
DECLARE @tblLookup TABLE (ID INT IDENTITY(0,1) NOT NULL, Value BIGINT)
INSERT INTO @tblLookup VALUES (0)
INSERT INTO @tblLookup VALUES (1996959894)
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DECLARE @crc BIGINT, @len INT, @i INT, @index INT
DECLARE @tblval BIGINT
SET @crc = 0xFFFFFFFF
SET @len = LEN(@input)
SET @i = 1

WHILE @i <= @len
BEGIN
    SET @index = ((@crc & 0xff) ^ ASCII(SUBSTRING(@input, @i, 1)))  
    SET @tblval = (SELECT Value FROM @tblLookup WHERE ID = @Index)
    SET @crc = (@crc / 256) ^ @tblval   
    SET @i = @i + 1 
END
SET @crc = ~@crc

SELECT @crc as CRC32, CONVERT(VARBINARY(4), @crc) as CRC32Hex

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