mysql on duplicate key code example

Example 1: mysql insert on dupèlicate

INSERT INTO table_name(c1)
VALUES(c1)
ON DUPLICATE KEY UPDATE c1 = VALUES(c1) + 1;

Example 2: find duplicate keys in mysql

SELECT col, COUNT(col) FROM table_name GROUP BY col HAVING COUNT(col) > 1;

Example 3: mysql on duplicate key update

INSERT INTO t1 (a,b,c) VALUES (1,2,3)
  ON DUPLICATE KEY UPDATE c=3;
INSERT INTO t1 (a,b,c) VALUES (4,5,6)
  ON DUPLICATE KEY UPDATE c=9;

Example 4: mysql on duplicate key update

UPDATE t1 SET c=c+1 WHERE a=1 OR b=2 LIMIT 1;