If you have 2 tables like below:

    Table1    A1    B1          Table2      B2     C2 
              -     -                       -     -
              1     2                       1     1
              2     4                       2     4
              3     5                       5     2

If you use Inner Join you get:

     A1     B1     B2      C2  
     -      -      -       -
     1      2      2       4
     3      5      5       2

If you use Full Outer Join you get:

     A1     B1     B2      C2  
     -      -      -       -
     1      2      2       4
     3      5      5       2
     2      4    NULL     NULL
    NULL   NULL    1       1

If you use Left Outer Join you get:

     A1     B1     B2      C2  
     -      -      -       -
     1      2      2       4
     3      5      5       2
     2      4    NULL     NULL