选择两个表之间的完全匹配

Question

I have two tables

t1

col1    col2
A        1
A        2 
B        1
C        2

t2

col1
1
2

I want to retrieve the records in tab1 which match all the records in tab2,

For the given scenario, I want to output A only because it has both 1 and 2 in col2 where as B and C has only a 1 or a 2 (not both).

Answer 1

You can write the query this way:

select t1.col1
from t1 join
     t2
     on t1.col2 = t2.col1
group by t1.col1
having count(distinct t1.col2) = (select count(distinct t2.col1) from t2);

This counts the number of matching values in the first table and compares it to the total number of values in the table.