CREATE TABLE #Tmp (
MyColumn Int Identity(1,1),
MyDescription varchar(100)
)

Create Table #Tmp2 (
 ACol int 
)

Insert into  #Tmp 
Values ('Hello'),('World'),('Mom')

Insert into #Tmp2
Values (1),(2),(3),(4)


Select MyColumn 
from #Tmp
Where MyColumn In (Select MyColumn from #Tmp2) 

Select MyColumn 
from #Tmp
Where MyColumn In (Select xyz from #Tmp2) 

CREATE TABLE Table1 (Col1 INT);
CREATE TABLE Table2 (Col2 INT);

SELECT Col1 FROM Table1 WHERE EXISTS (select 1 FROM Table2 where col2 = col1) -- col1 in Table 1, Col2 in table 2

Select * from Student where Student.student_id in (Select emp.student_id from emp)

We walk in the dark places no others will enter
We stand on the bridge and no one may pass