mysql duplicates with LOAD DATA INFILE

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.

Answer 2

It looks as if there actually is something you can do when it comes to duplicate rows for LOAD DATA calls. However, the approach that I've found isn't perfect: it acts more as a log for all deletes on a table, instead of just for LOAD DATA calls. Here's my approach:

Table test:

CREATE TABLE test (
    id INTEGER PRIMARY KEY,
    text VARCHAR(255) DEFAULT NULL
);

Table test_log:

CREATE TABLE test_log (
    id INTEGER, -- not primary key, we want to accept duplicate rows
    text VARCHAR(255) DEFAULT NULL,
    time TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

Trigger del_chk:

delimiter //
drop trigger if exists del_chk;
CREATE TRIGGER del_chk AFTER DELETE ON test
FOR EACH ROW
BEGIN
    INSERT INTO test_log(id,text) values(OLD.id,OLD.text);
END;//
delimiter ;

Test import (/home/user/test.csv):

1,asdf
2,jkl
3,qwer
1,tyui
1,zxcv
2,bnm

Query:

LOAD DATA INFILE '/home/ken/test.csv'
REPLACE INTO TABLE test 
FIELDS 
    TERMINATED BY ','
LINES
    TERMINATED BY '\n' (id,text);

Running the above query will result in 1,asdf, 1,tyui, and 2,jkl being added to the log table. Based on a timestamp, it could be possible to associate the rows with a particular LOAD DATA statement.