SQL Server中的DATALENGTH VARCHAR

根據MSDN，VARCHAR數據類型的存儲大小是輸入數據的實際長度+ 2個字節。我試圖理解爲什麼當我運行此查詢：SQL Server中的DATALENGTH VARCHAR

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

@VARCHAR的存儲大小是一樣的，因爲它是一個CHAR數據類型，這是25而不是27（25 + 2）。

它與DATALENGTH函數有關嗎？

來源

2015-04-23 Hernan Demczuk

datalength會告訴你數據的字節數，它不包括數據在存儲之前的2個字節。 VARCHAR類型的2字節的開銷是記錄在字符串中的字節數 - 即在你的案件25

來源

2015-04-23 00:56:45

我明白了。有沒有函數或sp來獲取它需要的存儲字節數？ –

'DATALENGTH（@VARCHAR）+ 2' :) –

DATALENGTH返回bytes used

LEN回報characters used

數數只是比較這些結果

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

你也可以輕鬆地添加+2您DATALENGTH爲VARCHAR數據類型

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

輸出

Bytes Characters ActualUsedBytes 
25  25   27

來源

2015-04-23 02:12:07 sqluser

SQL Server中的DATALENGTH VARCHAR

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