Friday, March 23, 2012

Declaring VARCHAR without length

Do you find anything wrong with this script?

CREATE PROCEDURE uspProcedureName
      @param1 VARCHAR
AS
....
....

If you aren't sure may be you should read this post completely without fail :)

All this while I was thinking that it is a well known issue until last week I saw a stored procedure something similar to the one shown above. Who ever created that stored procedure hasn't bothered to specify the length. Before jumping into the explanation of why we should SPECIFY THE LENGTH ALWAYS let us do a small exercise to understand this better.

Guess the results:

Try to answer what would be the output before checking the result.

--Declaring a variable without specifying the length
DECLARE @strSentence VARCHAR
SET @strSentence = 'Rajinikanth is always the NO 1 hero of India'
SELECT @strSentence

Expected Output: Rajinikanth is always the NO 1 hero of India
Actual Output: R

--While CASTing / CONVERTing
--The given string has 36 characters.
SELECT CONVERT(VARCHAR, '123456789123456789123456789123456789');
SELECT CAST('123456789123456789123456789123456789' AS VARCHAR);

Expected Output: 123456789123456789123456789123456789
Actual Output: 123456789123456789123456789123

As you could see for Variables the default length for VARCHAR is 1. When used within CONVERT/CAST the default length for VARCHAR is 30. 

So if we don't specify the length ourself these are the default values SQL Server uses - which means the data what we would be expecting to get stored in the database would have got silently truncated without our knowledge. These are one such tricky issues which if we aren't aware would mean we have to spend hell a lot of time debugging our scripts at a later stage.

Now to answer the first question on what is wrong with this script let us create a sample table and a stored procedure similar to that and see what it does.

--Sample table
CREATE TABLE dbo.tblDemo
(
ID INT,
FirstName VARCHAR(30)
)
GO

--Stored Procedure to Insert data into the sample table
CREATE PROCEDURE dbo.uspInsertData
@ID INT,
@FName VARCHAR -- See there is no length specified here
AS
BEGIN
    SET NOCOUNT ON;
    INSERT INTO dbo.tblDemo VALUES (@ID, @FName)
END
GO

--Test
EXEC dbo.uspInsertData 10, 'Vadivel'
GO
SELECT ID, FirstName FROM dbo.tblDemo
GO

The output would be just 'V'. Once again the data has got truncated silently. So ALWAYS SPECIFY THE LENGTH OF THE STRING WITHOUT FAIL.


--Clean Up
DROP PROC dbo.uspInsertData;
DROP TABLE dbo.tblDemo;

1 comment:

pragadesh said...

Realy Useful Sir