ON DUPLICATE KEY UPDATE

When you're doing an INSERT query, you could be trying to insert a row containing a primary key that already exists in the table. Instead of doing a previous query to see if the key exists or not, you could try ON DUPLICATE KEY UPDATE.

INSERT INTO table (
  field1, 
  field2
) 
VALUES (
  "foo", 
  "bar"
) 
ON DUPLICATE KEY UPDATE 
  field1="foo", 
  field2="bar"