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sql server Implicit cast or convert data type

Hi Expert,

I try to test @X, the following code has error, I like to know @X is Int or character data type here?

declare @X varchar(5);
set @X = 12345;
SELECT 
CASE 
      WHEN isnumeric(@X)=1
       THEN 'Yes'
       ELSE 'No'
END AS [Test],

Open in new window


Thanks in advance
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dshi15
Asked:
dshi15
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2 Solutions
 
Jim HornMicrosoft SQL Server Developer, Architect, and AuthorCommented:
Since @x is declared a varchar, to assign a value to it you have to surround that value with single quote marks

set @x = '12345'
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dshi15Author Commented:
Thank you , I knew that, but I want to know when implicit convert happened, or not?


declare @X varchar(5);
set @X = 12345;
SELECT @X;

This code work and result is 12345. I like to know this 12345 is varchar type or not?
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Jim HornMicrosoft SQL Server Developer, Architect, and AuthorCommented:
> declare @X varchar(5);
> I like to know this 12345 is varchar type or not?

I really don't understand your question.  @x is explicitly declared as a varchar(5) value in the first line above, and whether the second line assigns it a value to it of '12345', 'wahoo', NULL, or '-1' doesn't change that.

The ISNUMERIC() function will return if the value inside @x can be converted to a number, but that doesn't change the fact that @x is a varchar(5).
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dshi15Author Commented:
I changed "," to ";" now code is working and without error


declare @X varchar(5);
set @X = 12345;
SELECT 
CASE 
      WHEN isnumeric(@X)=1
       THEN 'Yes'
       ELSE 'No'
END AS [Test];

Open in new window


result is Yes, it is means @X is stored a integer 12345?
0
 
Jim HornMicrosoft SQL Server Developer, Architect, and AuthorCommented:
The ; at the end of a line is not necessary, with the sole exception I can think of being the line before a Common Table Expression (CTE) statement.

The comma is correct in that it didn't belong there, but the way you posted the code block in the original question I assumed that there was more to the SQL Statement that was not copy-pasted into the question because it was not relevant.
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dshi15Author Commented:
' ; ' is not important, it is syntax error, but my question is @X is stored a integer 12345? or not, (I try to understand implicit convert data type).
0
 
Jim HornMicrosoft SQL Server Developer, Architect, and AuthorCommented:
>but my question is @X is stored a integer 12345?
NO.

Because @x was declared varchar(5), the 12345 is stored AS A VARCHAR.
The fact that it is also an int is not relevant.

If you wish it to be stored as an integer, which is best practice if all of these values are numeric with no decimals, then you need to declare @x as an int.

Declare @x int
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Scott PletcherSenior DBACommented:
>> is @X is stored a integer 12345? <<

No.  Always remember that in SQL Server, like all other DBMSs, the input format doesn't necessarily reflect the internal format of the data.


Btw, to check for integer values, you must LIKE as below, because ISNUMERIC() has to handle many data types besides just int:


SELECT
CASE WHEN x LIKE '%[^0-9]%'
     THEN 'No'
     ELSE 'Yes'
     END AS [Test_X_For_int],
CASE WHEN isnumeric(x) = 0
     THEN 'No'
     ELSE 'Yes'
     END AS [Test_X_For_ISNUMERIC]
FROM (
    SELECT CAST(12345 AS varchar(5)) AS x UNION ALL
    SELECT ',' UNION ALL
    SELECT '1D0'
) AS test_data
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dshi15Author Commented:
I'm confused, I run this code, and result is 'Yes'

declare @X varchar(5);
set @X = 12345;
SELECT
CASE
      WHEN isnumeric(@X)=1
       THEN 'Yes'
       ELSE 'No'
END AS [Test];

I run this code and all results are 'Yes'


declare @X varchar(5);
set @X = 12345;
CASE WHEN x LIKE '%[^0-9]%'
     THEN 'No'
     ELSE 'Yes'
     END AS [Test_X_For_int],
CASE WHEN isnumeric(x) = 0
     THEN 'No'
     ELSE 'Yes'
     END AS [Test_X_For_ISNUMERIC]
FROM (
    SELECT CAST(12345 AS varchar(5)) AS x UNION ALL
    SELECT ',' UNION ALL
    SELECT '1D0'
) AS test_data
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Jim HornMicrosoft SQL Server Developer, Architect, and AuthorCommented:
>I run this code, and result is 'Yes'
The VALUE INSIDE @x, which during code execution is '12345', can convert to the integer data type.
This is NOT THE SAME as the variable @x being an integer.

So ... using simple English with as few technical terms as possible, what exactly are you asking us?
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