SQL Server - Fix Error -Must declare the scalar variable "@ID".

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Msg 137, Level 15, State 2, Line 6
Must declare the scalar variable "@ID".

To Fix it - replace

Declare @ID  int = (Select Top 1 ID From Customers Where [FisrtName] = 'Bob')
GO

Select @ID

with

Declare @ID  int = (Select Top 1 ID From Customers Where [FisrtName] = 'Bob')

Select @ID