CASE WHEN THEN (Return Column) ELSE END -

CASE WHEN THEN (Return Column) ELSE END -

i'm new sql , utilize excel, using oracle bi , need add together column following.

=if(a1="eg123456",b1,"")

i've got far.

case when "table1"."clientnumber" = 'eg123456' "table1"."bookingid" else '' end

it accepts formula when go view results says "view display error"

any help appreciated.

case