Oracle SQL：将选择从一个表插入到另一个表中，其中用户具有带有订单号的多个条目

Question

Table A

User | Order | Type | Contact
1001, 2, email, ijk@test.com
1001, 1, cell, 1234567890
1001, 3, home, 9876543210
1002, 1, home, 1234567891
1002, 2, cell, 1987654321
1003, 1, email, abc@test.com

Table B

User | Email
1001, def@test.com
1002, geh@test.com
1003, abc@test.com

I would like to insert a row into Table A using the data from Table B and the max order number for that user with the following:
If there is no email address in Table A for that user, insert the email address from Table B with max order number.
If the email in Table A is the same as the email in Table B for that user, do not insert anything.
If the email in Table A is different from the email in Table B for that user, insert the email address from Table B with max order number.

Output for the above should be insert into Table A*

1001, 4, email, def@test.com
1002, 3, email, geh@test.com

I have tried this multiple ways and keep hitting a wall. Any suggestions on what route to take?

Answer 1

If I understand correctly, you can do this with a single insert statement:

insert into tableA(user, order, type, contact)
    select user, maxorder + 1, 'email', email
    from tableB b cross join
         (select max(order) as maxorder from tableA) const
    where not exists (select 1
                      from tableA a
                      where b.user = a.user and b.contact = a.contact
                     );

Note: some of the identifiers you have used, such as order , are reserved words. I haven't bothered to escape them, assuming they are just examples.