if

if<condition_1>.
<statements...>
endif.

if...else

if<condition_1>.
  <statement block 1>.
else.
  <statement block 2>.
endif.

嵌套if

if<condition_1>.
<statement block>.
if<condition_2>.
<statement block>.
else.
<statement block>.
endif.
else <statement block>.
endif.

case

case <field>.
when <abc>.
  <statement block>.
when <def>.
  <statement block>.
when <pqr>,
  <statement block>.
...
...
when <xyz>.
    <statement block>.
when others.
  <statement block>.
endcase.