“INSERT IGNORE” vs “INSERT … ON DUPLICATE KEY UPDATE”

Question

While executing an INSERT statement with many rows, I want to skip duplicate entries that would otherwise cause failure. After some research, my options appear

Answer 1

Adding to this. If you use both INSERT IGNORE and ON DUPLICATE KEY UPDATE in the same statement, the update will still happen if the insert finds a duplicate key. In other words, the update takes precedence over the ignore. However, if the ON DUPLICATE KEY UPDATE clause itself causes a duplicate key error, that error will be ignored.

This can happen if you have more than one unique key, or if your update attempts to violate a foreign key constraint.

CREATE TABLE test 
 (id BIGINT (20) UNSIGNED AUTO_INCREMENT, 
  str VARCHAR(20), 
  PRIMARY KEY(id), 
  UNIQUE(str));

INSERT INTO test (str) VALUES('A'),('B');

/* duplicate key error caused not by the insert, 
but by the update: */
INSERT INTO test (str) VALUES('B') 
 ON DUPLICATE KEY UPDATE str='A'; 

/* duplicate key error is suppressed */
INSERT IGNORE INTO test (str) VALUES('B') 
 ON DUPLICATE KEY UPDATE str='A';