You can't do precisely that, but you can have a join with conditional logic, or you could have an inline sub-query in a case statement if you just want one column from the other tables.

For example:

select *

from Table1

left outer join Table2

on Table1.Col2 = Table2.Col2

and Table1.Col1 = 2

left outer join Table3

on Table1.Col2 = Table3.Col2

and Table1.Col1 = 3;

or

select *,

case Col1

when 2 then

(select Col3

from Table2

where Col2 = Table1.Col2)

when 3 then

(select Col3

from Table3

where Col2 = Table1.Col2)

end

from Table1;

The first one joins to both tables, but only pulls data from Table2 when Col1 = 2, and only pulls data from Table3 when Col1 = 3.

The second one pulls one column of data from Table2 or Table3, depending on the value of Col1 in Table1.

Does that help?