Newbie MySQL question - create if doesn't exist otherwise update?

Question

Uhh... kinda strange to put it into words that short.

Anyway what I want is in PHP to update an entry in a table if it does exist, otherwise create a new one filling it with the same data.

I know that's easy, but I'm relatively new to MySQL in terms of how much I've used it ._.

Answer 1

Look up REPLACE in the MySQL manual.

REPLACE works exactly like INSERT, except that if an old row in the table has the same value as a new row for a PRIMARY KEY or a UNIQUE index, the old row is deleted before the new row is inserted. See Section 12.2.5, “INSERT Syntax”.

REPLACE is a MySQL extension to the SQL standard. It either inserts, or deletes and inserts. For another MySQL extension to standard SQL — that either inserts or updates — see Section 12.2.5.3, “INSERT ... ON DUPLICATE KEY UPDATE Syntax”.

If you have the following INSERT query:

INSERT INTO table (id, field1, field2) VALUES (1, 23, 24)

This is the REPLACE query you should run:

REPLACE INTO table (id, field1, field2) VALUES (1, 23, 24)

Answer 2

Use 'REPLACE INTO':

 REPLACE INTO table SET id = 42, foo = 'bar';

See more in the MySQL documentation

Answer 3

A lot of developers still execute a query to check if a field is present in a table and then execute an insert or update query according to the result of the first query. Try using the ON DUPLICATE KEY syntax, this is a lot faster and better then executing 2 queries. More info can be found here

INSERT INTO table (a,b,c) VALUES (4,5,6) ON DUPLICATE KEY UPDATE c=9;

if you want to keep the same value for c you can do an update with the same value

INSERT INTO table (a,b,c) VALUES (4,5,6) ON DUPLICATE KEY UPDATE c=6;

the difference between 'replace' and 'on duplicate key':

replace: inserts, or deletes and inserts

on duplicate key: inserts or updates

if your table doesn't have a primary key or unique key, the replace doesn't make any sense.

Answer 4

As the others have said, REPLACE is the way to go. Just be careful using it though, since it actually does a DELETE and INSERT on the table. This is fine most of the time, but if you have foreign keys with constraints like ON DELETE CASCADE, it can cause some big problems.