oracle decode函数 和 case when

select decode(to_char(B.LQSJ, 'hh24:mi:ss'),
'00:00:00',
to_char(B.LQSJ, 'yyyy-mm-dd') || ' ' || '01:01:01',
to_char(B.LQSJ, 'yyyy-mm-dd hh24:mi:ss'))
from pcxx b

select decode('表达式', '如果A', '则A', '如果B', '则B', '其他')

select case to_char(B.LQSJ, 'hh24:mi:ss')
when '00:00:00' then
to_char(B.LQSJ, 'yyyy-mm-dd') || ' ' || '01:01:01'
else
to_char(B.LQSJ, 'yyyy-mm-dd hh24:mi:ss')
end case
from pcxx b

select  case'表达式' when 'A' then 'A1' when 'B' then 'B1' else end case