Must declare the scalar variable

You can't concatenate an int to a string. Instead of:

SET @sql = N'DECLARE @Rt int; SET @Rt = ' + @RowTo;

You need:

SET @sql = N'DECLARE @Rt int; SET @Rt = ' + CONVERT(VARCHAR(12), @RowTo);

To help illustrate what's happening here. Let's say @RowTo = 5.

DECLARE @RowTo int;
SET @RowTo = 5;


DECLARE @sql nvarchar(max);
SET @sql = N'SELECT ' + CONVERT(varchar(12), @RowTo) + ' * 5';
EXEC sys.sp_executesql @sql;

In order to build that into a string (even if ultimately it will be a number), I need to convert it. But as you can see, the number is still treated as a number when it's executed. The answer is 25, right?

In your case you can use proper parameterization rather than use concatenation which, if you get into that habit, you will expose yourself to SQL injection at some point (see this and this:

SET @sql = @sql + ' WHERE RowNum BETWEEN @RowFrom AND @RowTo;';


EXEC sys.sp_executesql @sql,
N'@RowFrom int, @RowTo int',
@RowFrom, @RowTo;

Just FYI, I know this is an old post, but depending on the database COLLATION settings you can get this error on a statement like this,

SET @sql = @Sql + ' WHERE RowNum BETWEEN @RowFrom AND @RowTo;';

if for example you typo the S in the

SET @sql = @***S***ql

sorry to spin off the answers already posted here, but this is an actual instance of the error reported.

Note also that the error will not display the capital S in the message, I am not sure why, but I think it is because the

Set @sql =

is on the left of the equal sign.

Case Sensitivity will cause this problem, too.

@MyVariable and @myvariable are the same variables in SQL Server Man. Studio and will work. However, these variables will result in a "Must declare the scalar variable "@MyVariable" in Visual Studio (C#) due to case-sensitivity differences.

Just adding what fixed it for me, where misspelling is the suspect as per this MSDN blog...

When splitting SQL strings over multiple lines, check that that you are comma separating your SQL string from your parameters (and not trying to concatenate them!) and not missing any spaces at the end of each split line. Not rocket science but hope I save someone a headache.

For example:

db.TableName.SqlQuery(
"SELECT Id, Timestamp, User " +
"FROM dbo.TableName " +
"WHERE Timestamp >= @from " +
"AND Timestamp <= @till;" + [USE COMMA NOT CONCATENATE!]
new SqlParameter("from", from),
new SqlParameter("till", till)),
.ToListAsync()
.Result;

You can also get this error message if a variable is declared before a GOand referenced after it.

See this question and this workaround.

Just an answer for future me (maybe it helps someone else too!). If you try to run something like this in the query editor:

USE [Dbo]
GO


DECLARE @RC int


EXECUTE @RC = [dbo].[SomeStoredProcedure]
2018
,0
,'arg3'
GO


SELECT month, SUM(weight) AS weight, SUM(amount) AS amount
FROM SomeTable AS e
WHERE year = @year AND type = 'M'

And you get the error:

Must declare the scalar variable "@year"

That's because you are trying to run a bunch of code that includes BOTH the stored procedure execution AND the query below it (!). Just highlight the one you want to run or delete/comment out the one you are not interested in.

If someone else comes across this question while no solution here made my sql file working, here's what my mistake was:

I have been exporting the contents of my database via the 'Generate Script' command of Microsofts' Server Management Studio and then doing some operations afterwards while inserting the generated data in another instance.

Due to the generated export, there have been a bunch of "GO" statements in the sql file.

What I didn't know was that variables declared at the top of a file aren't accessible as far as a GO statement is executed. Therefore I had to remove the GO statements in my sql file and the error "Must declare the scalar variable xy" was gone!

This is most likely not an answer to the issue itself but this question pops up as first result when searching for Sql declare scalar variable hence i share a possible solution to this error.

In my case this error was caused by the use of ; after a SQL statement. Just remove it and the error will be gone.

I guess the cause is the same as @IronSean already posted in an comment above:

it's worth noting that using GO (or in this case ;) causes a new branch where declared variables aren't visible past the statement.

For example:

DECLARE @id int
SET @id = 78


SELECT * FROM MyTable WHERE Id = @var; <-- remove this character to avoid the error message
SELECT * FROM AnotherTable WHERE MyTableId = @var

Sometimes, if you have a 'GO' statement written after the usage of the variable, and if you try to use it after that, it throws such error. Try removing 'GO' statement if you have any.

Give a 'GO' after the end statement and select all the statements then execute

As stated in https://learn.microsoft.com/en-us/sql/t-sql/language-elements/sql-server-utilities-statements-go?view=sql-server-ver16 , the scope of a user-defined variable is batch dependent .

--This will produce the error

 GO
DECLARE @MyVariable int;
SET @MyVariable = 1;
GO --new batch of code
SELECT @MyVariable--CAST(@MyVariable AS
int);
GO

--This will not produce the error

 GO
DECLARE @MyVariable int;
SET @MyVariable = 1;
SELECT @MyVariable--CAST(@MyVariable AS int);
GO

We get the same error when we try to pass a variable inside a dynamic SQL:

GO
DECLARE @ColumnName VARCHAR(100),
@SQL NVARCHAR(MAX);
SET @ColumnName = 'FirstName';
EXECUTE ('SELECT [Title],@ColumnName FROM Person.Person');
GO

--In the case above @ColumnName is nowhere to be found, therefore we can either do:

EXECUTE ('SELECT [Title],' +@ColumnName+ ' FROM Person.Person');

or

GO
DECLARE @ColumnName VARCHAR(100),
@SQL NVARCHAR(MAX);
SET @ColumnName = 'FirstName';
SET @SQL = 'SELECT ' + @ColumnName + ' FROM Person.Person';
EXEC sys.sp_executesql @SQL
GO