Compare Select 1 vs Select * in SQL Server

result.txt

 Table 'test'. Scan count 1, logical reads 2, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

 if exists(select 1 from test)
  |--Compute Scalar(DEFINE:([Expr1004]=CASE WHEN [Expr1005] THEN (1) ELSE (0) END))
       |--Nested Loops(Left Semi Join, DEFINE:([Expr1005] = [PROBE VALUE]))
            |--Constant Scan
            |--Clustered Index Scan(OBJECT:([master].[dbo].[test].[ck_test1]))

 Table 'test'. Scan count 1, logical reads 2, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

 if exists(select 1 from test)
  |--Compute Scalar(DEFINE:([Expr1004]=CASE WHEN [Expr1005] THEN (1) ELSE (0) END))
       |--Nested Loops(Left Semi Join, DEFINE:([Expr1005] = [PROBE VALUE]))
            |--Constant Scan
            |--Clustered Index Scan(OBJECT:([master].[dbo].[test].[ck_test1]))

select_1_vs_select_star.sql

select id into test from sysobjects
create clustered index ck_test1 on test(id)

set statistics io on
set statistics profile on 

if exists(select * from test) 
 begin 
   print 'yes'
 end 

if exists(select 1 from test) 
 begin 
   print 'yes'
 end