Methods for importing records from remote Oracle that do not exist on the same table in the local

Scenario: There is a table A on the remote Oracle, and a table B with the same table structure exists locally. Due to the fact that a few records from the business system operation were saved in the table B, and some of the records in a were originally imported, none of the records in a are saved. There are 15 records in A, B holds 3 records in A and B has 4 records generated by the local business system, and the 4 records generated by the business system in B cannot be deleted. Now I want to import the other 12 records from a into B, and I can keep the original 4 records from the business system in B.

Resolve sql:

1, first in a to get the record in B appears.

SELECT * FROM [email protected]_name a Where exists

(SELECT * from b b wherer b.colume1=a.colume1 and b.colume2=a.colume2 and B.colume3=a.colume3)

2. Obtain a record exists in B that has not been replaced by the not exists;

3. Insert a record that does not appear in B

INSERT INTO B

SELECT * FROM [e-mail Protected]_name a where NOT exists

(SELECT * from b b wherer b.colume1=a.colume1 and b.colume2=a.colume2 and B.colume3=a.colume3);

Note: Using this method to import data avoids importing duplicate records (in the absence of a primary key constraint in the table). If there is a PRIMARY key constraint on a field in the table, the primary KEY constraint is violated if it is not imported in a way that distinguishes it from the nonexistent data.