How to create a column on a SQL table, based on values of another table

Question

I currently have 2 SQL tables: table1 and table2 . table1 has 2 columns called id_a and column_a . table2 has 2 columns called id_b and column_b .

I would like to create a new_column in table1 . The value of new_column should be 1 if the value of table1.id_a exists in table2.id_b . Otherwise, new_column should have the value of 0.

How do I do this? I'm using SQLite3 and table1 is significantly larger than table2 .

Answer 1

How about a simple exists ?

select t1.*,
       (case when exists (select 1 from table2 t2 where t2.id_b = t1.id_a)
             then 1 else 0
        end) as flag
from table1 t1

Answer 2

A left join solution for fun! In certain circumstances might even be more efficient than correlated subquery as well.

select
    t1.*,
    case 
        when t2.id_b is null then 0
        else 1
    end as new_column
from
    table1 t1
left join
    table2 t2
    on t2.id_b = t1.id_a

Answer 3

How about a simple IN ?

SELECT *,
       id_a IN (SELECT id_b FROM table2) AS flag
FROM table1;