Is it possible to use IF statement in WHERE clause and use INTO statement according to different IF values?

is there any way to get these 2 SELECTs as one SELECT using something like IF in WHERE clause? And would using 1 select instead of 2 like this make any runtime difference? I'm using OpenSQL on SAP-ABAP. Providing code would be very helpful. TY.

SELECT SINGLE x FROM table WHERE y = a INTO lv_x.

SELECT SINGLE x FROM table WHERE y = b INTO lv_x.