Question

根据MSDN，VARCHAR数据类型的存储大小是输入数据的实际长度+ 2个字节。我试图理解为什么当我运行这个查询时：

DECLARE @VARCHAR VARCHAR(40) = 'RACING CLUB DE AVELLANEDA'
SELECT DATALENGTH(@VARCHAR) AS Bytes, LEN(@VARCHAR) AS Characters;

@VARCHAR的存储大小与CHAR数据类型相同，它是25而不是27（25 + 2）。

是否与DATALENGTH功能有关？

Answer 1

datalength将告诉您数据的字节数，它不包括存储中该数据之前的2个字节。 varchar的2字节开销用于记录字符串中的字节数 - 即在您的情况下为25

Answer 2

DATALENGTH会返回bytes used

的数量

LEN会返回characters used

的数量

只是比较这些结果

DECLARE @VARCHAR VARCHAR(40) = 'RACING CLUB DE AVELLANEDA'
SELECT DATALENGTH(@VARCHAR) AS Bytes, LEN(@VARCHAR) AS Characters;

Bytes: 25 ==> As it is a variable length, returns 25    
Characters: 25

DECLARE @VARCHAR CHAR(40) = 'RACING CLUB DE AVELLANEDA'
SELECT DATALENGTH(@VARCHAR) AS Bytes, LEN(@VARCHAR) AS Characters;

Bytes: 40 ==> As it is a fixed length, returns 40
Characters: 25

DECLARE @VARCHAR NVARCHAR(40) = 'RACING CLUB DE AVELLANEDA'
SELECT DATALENGTH(@VARCHAR) AS Bytes, LEN(@VARCHAR) AS Characters;

Bytes: 50 ==> As it is a variable length, returns 25*2 = 50
Characters: 25

DECLARE @VARCHAR NCHAR(40) = 'RACING CLUB DE AVELLANEDA'
SELECT DATALENGTH(@VARCHAR) AS Bytes, LEN(@VARCHAR) AS Characters;

Bytes: 80 ==> As it is a fixed length, returns 40*2 = 80
Characters: 25

您也可以轻松地将+2添加到DATALENGTH数据类型的VARCHAR

DECLARE @VARCHAR VARCHAR(40) = 'RACING CLUB DE AVELLANEDA'
SELECT  DATALENGTH(@VARCHAR) AS Bytes
        ,LEN(@VARCHAR) AS Characters
        ,DATALENGTH(@VARCHAR) + 2 AS ActualUsedBytes

输出

Bytes   Characters  ActualUsedBytes
25      25          27

SQL Server中的DATALENGTH VARCHAR

2 个答案: