Oracle updates more than one data

Select Sid, CJSJ
From BASE_ZJXX
where CJSJ = to_date (' 0001/1/1 ', ' yyyy/mm/dd ');

SELECT *
From Sys_user
where Qyid in (90656, 90655, 90646, 90641, 90636, 90633, 90631);

UPDATE base_zjxx
SET CJSJ = (case
When Zjid = ' 90656 ' Then
To_date (' 2015/4/7 15:57:49 ', ' yyyy/mm/dd hh24:mi:ss ')
When Zjid = ' 90655 ' Then
To_date (' 2015/4/7 14:45:15 ', ' yyyy/mm/dd hh24:mi:ss ')
When Zjid = ' 90646 ' Then
To_date (' 2015/4/3 10:45:01 ', ' yyyy/mm/dd hh24:mi:ss ')
When Zjid = ' 90641 ' Then
To_date (' 2015/4/2 9:43:55 ', ' yyyy/mm/dd hh24:mi:ss ')
When Zjid = ' 90636 ' Then
To_date (' 2015/4/1 15:58:11 ', ' yyyy/mm/dd hh24:mi:ss ')
When Zjid = ' 90633 ' Then
To_date (' 2015/4/1 14:32:58 ', ' yyyy/mm/dd hh24:mi:ss ')
When Zjid = ' 90631 ' Then
To_date (' 2015/4/1 10:30:23 ', ' yyyy/mm/dd hh24:mi:ss ')
ELSE
Cjsj
END)
where Zjid in (90656, 90655, 90646, 90641, 90636, 90633, 90631)

Update BASE_ZJXX T1 Set
T1.CJSJ =
(Select Create_date
From Sys_user T2
where T1.zjid = T2.sid) where
T1.CJSJ = to_date (' 0001/1/1 ', ' yyyy/mm/dd ')

Oracle updates more than one data