SQL & PL/SQL :: Adding Conditions In Where Clause

I am trying to run an SQL query which refers/joins around 10 tables.In my case I would want to add an if-else or case condition in the WHERE clause of select query

For example

select a.column1, b.column1, c.column1, d.column1
from a, b, c, d
WHERE a.column2 = b.column2
AND (if a.column3 = 10 then ( I want 2 conditions to be
AND b.column2 = c.column2) added
else after WHERE clause as AND...)
AND b.column2 = d.column2
)
AND d.column2 = a.column2