SQL Server 2005 Weird varchar Behavior
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;
produces:
Result1 = d Result2 = cat
I would expect either
- The assignment
SET @Test1 = 'dog';
to fail because there isn't enough room in@Test1
- Or the
SELECT
to return 'dog' in the Result1 co开发者_JS百科lumn.
What is up with @Test1
? Could someone please explain this behavior?
Let me answer with some quotes from the SQL Server documentation.
char and varchar
varchar[(n)]
...
When n is not specified in a data definition or variable declaration statement, the default length is 1.
Converting Character Data
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.
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
.
the varchar is defaulting to length one
DECLARE @Test1 varchar;
try this, which will uses a simple function that takes a sql_variant and returns the data type info back:
CREATE FUNCTION [dbo].[yourFunction]
(
@InputStr sql_variant --can not be varchar(max) or nvarchar(max)
)
returns
varchar(8000)
BEGIN
DECLARE @Value varchar(50)
--can use SQL_VARIANT_PROPERTY(@InputStr,'BaseType') to determine given datatype
--do whatever you want with @inputStr here
IF @InputStr IS NULL
BEGIN
SET @value= 'was null'
END
ELSE IF SQL_VARIANT_PROPERTY(@InputStr,'BaseType')='varchar'
BEGIN
--your special code here
SET @value= 'varchar('+CONVERT(varchar(10),SQL_VARIANT_PROPERTY(@InputStr,'MaxLength '))+') - '+CONVERT(varchar(8000),@InputStr)
END
ELSE IF SQL_VARIANT_PROPERTY(@InputStr,'BaseType')='datetime'
BEGIN
--your special code here
SET @value= 'datetime - '+CONVERT(char(23),@InputStr,121)
END
ELSE IF SQL_VARIANT_PROPERTY(@InputStr,'BaseType')='nvarchar'
BEGIN
--your special code here
SET @value= 'nvarchar('+CONVERT(varchar(10),CONVERT(int,SQL_VARIANT_PROPERTY(@InputStr,'MaxLength '))/2)+') - '+CONVERT(varchar(8000),@InputStr)
END
ELSE
BEGIN
--your special code here
set @value= 'unknown!'
END
RETURN @value
END
GO
DECLARE @Test1 varchar;
SET @Test1 = 'dog';
DECLARE @Test2 varchar(10);
SET @Test2 = 'cat';
SELECT @Test1 AS Result1, @Test2 AS Result2;
select [dbo].[yourFunction](@test1)
output:
Result1 Result2
------- ----------
d cat
(1 row(s) affected)
-------------------
varchar(1) - d
(1 row(s) affected)
moral of the story, don't be lazy, specify a length on all of your varchar values!!!
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