Oracle：用另一个表中的值更新列

Question

I added a new column to an existing table. I want to populate it with a value which I retrieve from another table.

Table: EXPORT

Name | email | employeeid | userid

Table: USER

id |  name  | email  | idnumber

The new column is EXPORT.userid , which I want to equal out to USER.id . Please note that id and idnumber are NOT the same - idnumber stores the employeeid while id is a auto-increment PK. USER.idnumber is equal to EXPORT.employeeid .

I want to populate EXPORT.userid with USER.id when export.employeeid = user.idnumber .

How can I do that with Oracle-compatible SQL-code?

I tried the following, but it throws me an error.

UPDATE EXPORT  
   SET userid = ( SELECT id 
                FROM USER 
               WHERE USER.idnumber = EXPORT.employeeid 
                 and USER.EMAIL = EXPORT.email) 
 WHERE EXISTS( SELECT 1
             FROM USER
            WHERE USER.idnumber = EXPORT.employeeid 
              and USER.EMAIL = EXPORT.email) 

But I get this error

[Error] Execution (2: 19): ORA-01427: single-row subquery returns more than one row

Answer 1

Probably, this subquery returns more than one row for given email and idnumber:

SELECT id 
                FROM USER 
               WHERE USER.idnumber = EXPORT.employeeid 
                 and USER.EMAIL = EXPORT.email

Try using DISTINCT to exclude duplicates:

SELECT DISTINCT id 
                FROM USER 
               WHERE USER.idnumber = EXPORT.employeeid 
                 and USER.EMAIL = EXPORT.email

Or add some sample data to your question. What is the unique key of tables USER and EXPORT?

Answer 2

Try running the following query

SELECT * FROM (
    SELECT USER.idnumber, USER.EMAIL, COUNT(*) AS cnt
    FROM USER
    GROUP BY USER.idnumber, USER.EMAIL
) c
WHERE c.cnt > 1

If you see any rows, then this is your problem.

For example, if you have a USER table that looks like

id |  name    |      email         | idnumber
1  | icefresh | icefresh@what.ever | 100
2  | icefresh | icefresh@what.ever | 100

Then your query

SELECT id 
FROM USER 
WHERE USER.idnumber = EXPORT.employeeid 
    and USER.EMAIL = EXPORT.email

Will return 1 and 2. In order for it to work, it can only return 1 value.