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.
This will work in MySQL. In the background it instruct the server to make inner join on two tables.
UPDATE Registration r, City c SET r.state_id = c.state_id WHERE r.city_id = c.city_id;
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)
不确定MySQL,但是可以在Oracle和SQL Server中完成:
UPDATE Registration r SET state_id = (SELECT state_id FROM City WHERE city_id = r.city_id)
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