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php – Create if an entry doesn't exist, otherwise update?

Posted by: admin April 23, 2020 Leave a comment

Questions:

Kinda strange to put it into words that short, heh.

Anyway, what I want is basically to update an entry in a table if it does exist, otherwise to 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 😛

How to&Answers:

Use ‘REPLACE INTO’:

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

See more in the MySQL documentation

Answer:

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.

You can also use the VALUES function to avoid having to specify the actual values twice. E.g. instead of

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

you can use

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

Where VALUES(c) will evaluate to the value specified prevously (6).

Answer:

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.

Answer:

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)