When I got this requirement, I thought of directly using the if...else... code to make judgments. The first is to query. If the record is found, it will be updated. If it is not found, the data will be inserted directly.
There is no problem with this method. After all, it can complete the requirements. However, because the records of this table in the database are really too large, it is too time-consuming to query and judge by means of code. After a query, this is the method to find the merge into of the Oracle database.
First, let's take a look at the basic syntax of merge into (a feature introduced in Oracle 9i):
MERGE INTO table_name alias1 USING (table|view|sub_query) alias2 ON (join condition) WHEN MATCHED THEN UPDATE table_name SET col1 = col_val1, col2 = col_val2 WHEN NOT MATCHED THEN INSERT (column_list) VALUES (column_values);
Maybe you don't know much about this syntax, so let's look at a simple example now:
merge into Students st using newStudents nst on (st.id = nst.id) when matched then update set st.name = nst.name when not matched then insert values(nst.id, nst.name, nst.sex)
The meaning of this sql means that if the id of the new student already exists in the database, when it is matched, the update operation is performed; when it is not matched, the insert operation is performed.
Compared with using code judgment to perform update or insert operations, the execution of SQL statements has undoubtedly been improved in terms of efficiency, so using merge into is still a good choice.
Because I am not familiar with the database, I didn't think of this kind of operation at the first time. I used it this time, and it was considered as learning. Record it, maybe it will be useful in the future.