sql - 使用子查询和重复项更新表

Question

我需要根据另一个表更新一个表，所以我有以下语句：

update FAULTS
set FAULTS.FAULT_STATE = (
    select INCIDENTS.TICKET_STATE from INCIDENTS
    where INCIDENTS.CF_ID = FAULTS.CF_ID
)

它给了我错误说：

ORA-01427: single-row subquery returns more than one row

我尝试了 DISTINCT，但状态值也不同，所以 DISTINCT 不起作用。所以我也改了：

update FAULTS
set FAULTS.FAULT_STATE = (
    select INCIDENTS.TICKET_STATE from INCIDENTS
    where INCIDENTS.CF_ID = FAULTS.CF_ID and rownum = 1
)

现在它不会给出错误。

问题是，如果子查询返回null，它也会更新行并清除内容。有什么解决办法吗？

Answer 1

您可以确保只更新匹配的行，如下所示：

update FAULTS
set FAULTS.FAULT_STATE = (
    select INCIDENTS.TICKET_STATE from INCIDENTS
    where INCIDENTS.CF_ID = FAULTS.CF_ID and rownum = 1
)
where exists (
    select INCIDENTS.TICKET_STATE from INCIDENTS
    where INCIDENTS.CF_ID = FAULTS.CF_ID
)

Answer 2

合并变体（10g+）：

merge into faults
using (select cf_id, ticket_state from incidents) incidents
   on (incidents.cf_id = faults.cf_id)
when matched then update
 set fault_state=ticket_state;