How to Join two tables and update a column?

Question

I have two tables as below

   TableA          TableB   
    ID1 ID2         ID1 ID3
    1   X           1   X
    2   NULL        2   A
    3   (NULL)      3   B
    4   (NULL)      4   C
    5   (NULL)      5   D

Expected Result:

    TableA  
   ID1  ID2
   1    X
   2    A
   3    B
   4    C
   5    D

My query:

     UPDATE TableA a LEFT JOIN TableB b  ON a.ID1 =  b.ID1
     SET a.ID2  = b.ID3 
     WHERE   a.ID2 is NULL OR  a.ID2 != b.ID3

But the above query is going in a loop. Thanks for your help in advance.

Answer 1

If your tables look exactly like the ones you have in your question then you have no need to join the tables, your resulting table is the table on the right.

select * 
from table b;