Question

When using LOAD DATA INFILE, is there a way to either flag a duplicate row, or dump any/all duplicates into a separate table?

Answer 1

From the LOAD DATE INFILE documentation:

The REPLACE and IGNORE keywords control handling of input rows that duplicate existing rows on unique key values:

• If you specify REPLACE, input rows replace existing rows. In other words, rows that have the same value for a primary key or unique index as an existing row. See Section 12.2.7, “REPLACE Syntax”.
• If you specify IGNORE, input rows that duplicate an existing row on a unique key value are skipped. If you do not specify either option, the behavior depends on whether the LOCAL keyword is specified. Without LOCAL, an error occurs when a duplicate key value is found, and the rest of the text file is ignored. With LOCAL, the default behavior is the same as if IGNORE is specified; this is because the server has no way to stop transmission of the file in the middle of the operation.

Effectively, there’s no way to redirect the duplicate records to a different table. You’d have to load them all in, and then create another table to hold the non-duplicated records.