While me and my friend roshan recently working as a support developers at Australia famous e-commerce website. recently roshan as assign a new bug in this site it’s related to the product synchronize process in the ware house product table and the e-commerce site, his main task was check the quickly the site product table and check with ware house product table product if the either insert new data into a site database, or update an existing record on the site database, Of course, doing a lookup to see if the record exists already and then either updating or inserting would be an expensive process (existing items are defined either by a unique key or a primary key). Luckily, MySQL offers two functions to combat this (each with two very different approaches).
1. REPLACE = DELETE+INSERT
2. INSERT ON DUPLICATE KEY UPDATE = UPDATE + INSERT
1 . REPLACE
This syntax is the same as the INSERT function. When dealing with a record with a unique or primary key, REPLACE will either do a DELETE and then an INSERT, or just an INSERT if use this this function will cause a record to be removed, and inserted at the end. It will cause the indexing to get broken apart, decreasing the efficiency of the table. If, however
REPLACE INTO ds_product SET pID = 3112, catID = 231, uniCost = 232.50, salePrice = 250.23;
2. ON DUPLICATE KEY UPDATE
ON DUPLICATE KEY UPDATE clause to the INSERT function. This one actively hunts down an existing record in the table which has the same UNIQUE or PRIMARY KEY as the one we’re trying to update. If it finds an existing one, you specify a clause for which column(s) you would like to UPDATE. Otherwise, it will do a normal INSERT.
INSERT INTO ds_product SET pID = 3112, catID = 231, uniCost = 232.50, salePrice = 250.23, ON DUPLICATE KEY UPDATE uniCost = 232.50, salePrice = 250.23;
This should be helpful when trying to create database queries that add and update information, without having to go through the extra step.
Thanks Have a Nice Day 
