How to write a Simple TSQL

Question

I have the following table:-

I have two requirements. the 1st one is, I need ColA and ColB when ColB is 1. So the query would be:-

Select ColA, ColB from Table1 where ColB =1.

The Output of the 1st requirement is:-

Now the 2nd requirement is, as the value of ColA is 2 when ColB =1, So I need ColA and ColB when ColA is 2. But the problem is that I don't know the value of ColA when ColB is 2. I simply can't write

Select ColA, ColB from Table1 where ColA =2.

The final output would be

Answer 1

Try this query:

select t2.*
from Table1 t1 
inner join Table1 t2 on t2.ColA = t1.ColB
where t1.ColB = 1