Conversion error in SQL server "the data types nvarchar(max) and varbinary(max) are incompatible in the add operator"

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I am using a varbinary type conversion on a variable in a dynamic query. I deal with dynamic query errors very well, and I know something is wrong while converting nvarchar(max) and varbinary(max) in a dynamic query.
But I am not able to find its solution.

SQL

DECLARE @Oldlogo	varbinary(max)
SET @Oldlogo = 'some binary code'
declare @query nvarchar(max)
SET @query = ''
SET @query = @query + '  IF EXISTS(SELECT 1 FROM  Company WHERE CONVERT(varbinary,Company_Logo_TopLeft) = CONVERT(varbinary,''' + @Oldlogo + ''')) '
	SET @query = @query + '  BEGIN '
	SET @query = @query + ' Do someting'	
       SET @query = @query + '   END '
SET @query = @query + '   ELSE'
       SET @query = @query + '  BEGIN '
	SET @query = @query + ' Do someting else'	
	SET @query = @query + '   END '
EXEC (@query)

Error message is
"The data types nvarchar(max) and varbinary(max) are incompatible in the add operator."
Any help?
Thanks

What I have tried:

I tried using parameter query and execute it with sp_executesql but no luck. used sp_executeSQL and @params

Posted 14-Mar-17 3:43am

Schatak

Updated 14-Mar-17 3:57am

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CHill60 14-Mar-17 9:51am

What about the error before that: "Msg 257, Level 16, State 3, Line 2
Implicit conversion from data type varchar to varbinary(max) is not allowed. Use the CONVERT function to run this query."

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OriginalGriff · Answer 1 · 2017-03-14T03:55:00

When you write this:

SQL

DECLARE @Oldlogo	varbinary(max)
... CONVERT(varbinary,Company_Logo_TopLeft) = CONVERT(varbinary,''' + @Oldlogo + ''')) '

You are trying to convert a VARBINARY value (from @OldLogo) to a VARCHAR (as part of your string concatenation) and then convert it back to a VARBINARY) via the CONVERT function)

You can't convert VARBINARY to VARCHAR - that kind of testing really needs to be done in your presentation layer rather than in SQL - and concatenating the binary value into a string (even if it worked) is an invitation for SQL Injection.
Why are you trying to do that as a dynamic query?
You could compare @OldLogo and Company_Logo_TopLeft with a simple '=' without making that dynamic at all.

CHill60 · Answer 2 · 2017-03-14T03:57:00

First fix the first problem:

Quote:
Implicit conversion from data type varchar to varbinary(max) is not allowed. Use the CONVERT function to run this query."

I did this like this:

SQL

SET @Oldlogo = convert(varbinary,'some binary code')

The problem you quote in your question is caused by :

SQL

SET @query = @query + '  IF EXISTS(SELECT 1 FROM  Company WHERE CONVERT(varbinary,Company_Logo_TopLeft) = CONVERT(varbinary,''' + @Oldlogo + ''')) '

It is not clear why you are trying to insert 'some binary code' and convert it to varbinary again.
Once you've sorted out what you are actually trying to do, replace

EXEC (@query)

with

PRINT @query

until you are completely happy that the SQL you are generating is correct.

It's a good idea to start with a specific set of data and do raw SQL statements so that you can work out how to build the dynamic SQL - i.e. don't just dive straight in

Conversion error in SQL server "the data types nvarchar(max) and varbinary(max) are incompatible in the add operator"

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