Question

There is a one table,

City[city_id,state_id]

There was another table in same database,

Registration[reg_id,city_id]

Now, i have added one more column into ‘Registration’ table, so it is become as shown below,

    Registration[reg_id,city_id,state_id]

But, the problem is that values of the state_id column is ‘0’. So, How can i insert value of state_id column of “Registration” table from the “City” table according to matching city_id value of “Registration” table.

Answer 1

As long as this query will be performed just once – you could use this not efficient, but readable query:

UPDATE Registration r
   SET state_id = (SELECT state_id
                     FROM City c
                    WHERE c.city_id = r.city_id)