Although the primary use is insertion, they can be used for updates ... mysql directly, oracle in a more round-about way.
The 'REPLACE' keyword in mysql's 'LOAD DATA' comment is record-by-record, based on the primary key of the table. If you're using autoincrement for for primary key, this isn't going to work for you. In the example given, however, there's a WHERE clause using the field 'vc', which I assumed was the primary key, or at least a unique index.
You're right that sqlldr doesn't handle this case. (its REPLACE keyword will remove the entire table, as will TRUNCATE. The only other option for tables w/ existing data is 'APPEND'.) However, you can use sqlldr to get the data into a temp table, and then use a pl/sql command to replace the records as needed (or insert into the temp tables those that don't have a corresponding record already). You'd have to benchmark it to see what's the best method for your specific situation.
If you're going to be designing a table that requires regular bulk updates, I'd highly recommend finding a suitable key (even if it's a composite key) and not use a sequence or autoincrement
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