从多个表中获取数据

Question

I have table 1 with columns

• userid
• deptname
• deptid
• working_in
• joining_date
• profession

Table 2 has columns

• userid
• salary
• doj
• user_mail

And table 3 contains

• userid
• deptname
• deptid
• salary

Both Table 1 and Table 2 contain some rows. Table 3 contains no rows.

The values of table 3 will be the combination of values from table 1 and table 2.

How do I update table 3 by fetching only the details userid , deptname , deptid , salary required from table 1 and table 2?

Answer 1

select t1.userid, t1.deptname, t1.deptid, t2.salary from table1 t1
join table2 t2
on t1.userid=t2.userid

That way you can, in a single query, get the details from both tables. Notice that I used the a join according to the "userid" column. That way the "salary" will be of the same user (assuming "userid" is a shared PK).

EDIT: In the example code above you don't insert anything. There is only a SELECT statement. That means, you're only extracting the relevant data from both table1 and table2. In order to put the data inside of table3 you need an INSERT stetment. You can look it up here http://www.techonthenet.com/oracle/insert.php , And it should end up something like :

INSERT INTO table3 
(userid, deptname, deptid, salary)
VALUES (select t1.userid, t1.deptname, t1.deptid, t2.salary from table1 t1
join table2 t2
on t1.userid=t2.userid)

Answer 2

Assuming that

1. your "Table 1" is named table_1 ,
2. your "Table 2" is named table_2 ,
3. your "Table 3" is named table_3 ,
4. your "combination of values" is a join between table 1 and table 2 on the userid column, and
5. your "I update table 3" means you want to store the "combination of values" into your table 3,

then your query would be:

insert into table_3 (userid, deptname, deptid, salary)
select userid, T1.deptname, T1.deptid, T2.salary
from table_1 T1
    join table_2 T2 using (userid)
;