How do I get data from one Google spreadsheet `A` into spreadsheet `B`?  
And when Spreadsheet `A` is modified, then Spreadsheet `B` also changes automatically.


**UPDATE:**


For example:


I have two spreadsheets  Documents DocA  and DocB

        A               B           C
    1    uid	            serial_no	ph
    2   356307042189331	3123958	    912345678900
    3   356307046077540	3966305	    923451245123
    4   356307046092465	3966407	    978458784578
    5   356307046098678	3970932	    971548745125


In DocB
  

        A               B
    1   serial_no      uid
    2   3123958
    3   3284728
    4   3284655

I am trying to get A2 from DocA into B2 in DocB with the following code

=QUERY(ImportRange("[key]","Sheet1!A:C"),"Select Col1, Col2 where Col1='"&A2&"'",1)

I get 

    uid	serial_no

in Cell B2 instead of the value in Cell A2 of DocA