Question

Due to a rather brilliant oversight in my current project, we have some guids getting stored in a varchar column in one table, which need to be compared to a uniqueidentifier column in another.

How can I do this? SQL server simply says it cannot convert from a character string to a uniqueidentifier.

Answer 1

If SQL complains it cannot cast it means not only you stored the uniqueidentifier as varchar, you used a different format than SQL Server (eg. you added the ‘{‘ and ‘}’). SQL is perfectly capable of casting string to uniqueidentifier when properly formatted:

declare @u uniqueidentifier;
declare @s varchar(64);

select @u = NEWID();
select @s = CAST(@u as varchar(64));
select CAST(@s as uniqueidentifier), @u, @s;

Depending on how you actualy stored the uniqueidentifier, you will most likely have tomodify the data and your code to match the SQL format (no {}).