oracle 修改某字段,判斷是否為空,如果為空賦默認值

update table_complaint t
set t.cptdatetime = nvl2(t.cptdatetime,
'',
to_char(to_date(t.cptdatetime,
'yyyy-mm-dd hh24:mi:ss') - 2))

where t.cpintid = 'djdjdj';