sql - How to update table2 with table1's id only on a unique match

Question

I have two tables:

table 1 with id, firstname and lastname

table 2 with t1_id, firstname and lastname

I'd like a SQL query (if possible, not a PL/SQL) to update table2 with table1's id when I have a unique match on firstname and lastname

the word "unique" here is my problem :

update table2 t2
set t1_id = (select id from table1 t1
    where t1.firstname=t2.lastname and t1.lastname=t2.lastname)

Whenever I have a match from t2 to multiple t1 records, I get the "ORA-01427: single-row subquery returns more than one row" error. Any clue to not update on multiple matches?

Thanks.

Answer 1

merge into table2 d
using (
  select firstname, lastname, max(id) id
  from table1 t1
  group by firstname, lastname
  having count(0) = 1
) s
on (d.firstname=s.firstname and d.lastname=s.lastname)
when matched then update set t1_id = s.id;

Answer 2

如果您想将 id 设置为 NULL 以防在 table1 中发现重复条目​​或根本没有条目，那么只需：

更新表 2 t2
设置 t1_id =
(
  当 min(id) = max(id) then min(id) else null end 时选择 case
  从表 1 t1
  其中 t1.firstname=t2.lastname 和 t1.lastname=t2.lastname
)

Answer 3

内部联接可以工作（至少对于 SQL Server）。

update  t1
set t1.id = t2.id 
FROM table1 t1 
INNER JOIN table t2 ON t1.firstname=t2.firstname and t1.lastname=t2.lastname

Answer 4

可能的解决方案是计算匹配的行数：

update table2 t2
set t1_id = 
            (
             select id 
             from table1 t1
             where t1.firstname=t2.lastname and t1.lastname=t2.lastname
            )
where 
(
 select count(*) 
 from table1 
 where t1.firstname = lastname and t1.lastname= lastname
) = 1