T-SQL GO Statement

It is a batch terminator
this will break

declare @i int
set @i =5

declare @i int
set @i =6

Select @i

Msg 134, Level 15, State 1, Line 5 The variable name '@i' has already been declared. Variable names must be unique within a query batch or stored procedure.
this will work

declare @i int
set @i =5

go
declare @i int
set @i =6

Select @i