问题描述
此 SQL Server 2005 T-SQL 代码:
This SQL Server 2005 T-SQL code:
DECLARE @Test1 varchar;
SET @Test1 = 'dog';
DECLARE @Test2 varchar(10);
SET @Test2 = 'cat';
SELECT @Test1 AS Result1, @Test2 AS Result2;
产生:
结果 1 = d结果 2 = 猫
我希望要么
- 赋值
SET @Test1 ='dog';失败，因为没有@Test1 有足够的空间 - 或者
SELECT在 Result1 列中返回dog".
- The assignment
SET @Test1 = 'dog';to fail because there isn't enough room in@Test1 - Or the
SELECTto return 'dog' in the Result1 column.
@Test1 怎么了?有人可以解释一下这种行为吗?
What is up with @Test1? Could someone please explain this behavior?
推荐答案
让我用 SQL Server 文档中的一些引述来回答.
Let me answer with some quotes from the SQL Server documentation.
char 和 varchar
varchar[(n)]
...
当数据定义或变量声明语句中未指定 n 时，默认长度为 1.
When n is not specified in a data definition or variable declaration statement, the default length is 1.
转换字符数据
当字符表达式转换为不同大小的字符数据类型时，对于新数据类型来说太长的值将被截断.
When character expressions are converted to a character data type of a different size, values that are too long for the new data type are truncated.
因此，您的 varchar 被声明为 varchar(1)，并且您的 SET 语句中的隐式转换(从长度为 3 的字符串文字到 varchar(1)) 将 dog 截断为 d.
So, your varchar is declared as a varchar(1), and the implicit conversion in your SET statement (from a string literal of length 3 to a varchar(1)) truncates dog to d.
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