使用外键将数据从一个表复制到另一个表

Question

i am facing a problem regarding sql query.

i have a table structure

TABLE_A

A_id : 10,20,30,40 
A_name: a,b,c,d  
B_id: null,null,null,null

TABLE_B

B_id: 1,2,3,4  
B_name:n1,n2,n3,n4 
A_id: 10,20,30

Now I need to copy the B_id from TABLE_A to B_id of TABLE_B where A_id of TABLE_A is same as A_id of TABLE_B

the table will then look like

TABLE_A

A_id : 10,20,30,40  
A_name: a,b,c,d   
B_id: 1,2,3,null

I have tried this:

UPDATE TABLE_A 
SET B_id = a.B_id
from TABLE_A a 
WHERE TABLE_A.A_id = a.A_id

but its not working and the error is SQLCODE=-104, SQLSTATE=42601

Answer 1

Have you tried this

UPDATE TABLE_A SET B_id = b.B_id 
from TABLE_B b 
WHERE TABLE_A.A_id = b.A_id

Answer 2

update TABLE_A A,TABLE_b B set A.b_id = B.b_id where A.a_id = B.a_id;

If you are working on mysql . Don't know other database will accept the syntax or not.