更好地加入以提高查询性能

Question

I need to select some date from multiple table in oracle. I have 2 tables, Table A and Table B which should be joined eachother. Let me describe it in table.

Table A

A_id    x_id    y_id   z_id    price ....

Table B

B_id    xyz_id    myValue

NOT : x_id, y_id and z_id keeps same value with (Table B).xyz_id

my query should return

A_id, x_id,   y_id,   z_id,  myValue for x_id, myValue for y_id, myValue for z_id

I manage that query like

select 
    A_id, 
    (select myValue as valueForX_id from TableB where xyz_id = x_id)
    (select myValue as valueForY_id from TableB where xyz_id = y_id)..,
from TableA;

but I don't know this will give best performance. I ask for your advice. Thanks.

Answer 1

This should get the values using joins. I think you will find this performs much faster for large datasets.

select a.A_id, a.x_id, a.y_id, a.z_id, x.myValue as x_value,yb.myValue as y_value, z.myValue as z_value
from TableA a
join TableB x on x.xyz_id = a.x_id
join TableB y on y.xyz_id = a.y_id
join TableB z on z.xyz_id = a.z_id