MySql Table Insert if not exist otherwise update

UPDATE AggregatedData SET datenum="734152.979166667", 
Timestamp="2010-01-14 23:30:00.000" WHERE datenum="734152.979166667";

It works if the datenum exists, but I want to insert this data as a new row if the datenum does not exist.

UPDATE

the datenum is unique but that's not the primary key

Jai is correct that you should use INSERT ... ON DUPLICATE KEY UPDATE.

Note that you do not need to include datenum in the update clause since it's the unique key, so it should not change. You do need to include all of the other columns from your table. You can use the VALUES() function to make sure the proper values are used when updating the other columns.

Here is your update re-written using the proper INSERT ... ON DUPLICATE KEY UPDATE syntax for MySQL:

INSERT INTO AggregatedData (datenum,Timestamp)
VALUES ("734152.979166667","2010-01-14 23:30:00.000")
ON DUPLICATE KEY UPDATE 
  Timestamp=VALUES(Timestamp)

Try using this: > If you specify ON DUPLICATE KEY UPDATE, and a row is inserted that would cause a duplicate value in a UNIQUE index or PRIMARY KEY, MySQL performs an [UPDATE](http://dev.mysql.com/doc/refman/5.7/en/update.html) of the old row... > The ON DUPLICATE KEY UPDATEclause can contain multiple column assignments, separated by commas. > WithON DUPLICATE KEY UPDATE, the affected-rows value per row is 1 if the row is inserted as a new row, 2 if an existing row is updated, and 0 if an existing row is set to its current values. If you specify the CLIENT_FOUND_ROWS flag to [mysql_real_connect()`](http://dev.mysql.com/doc/refman/5.7/en/mysql-real-connect.html) when connecting to mysqld, the affected-rows value is 1 (not 0) if an existing row is set to its current values...

I had a situation where I needed to update or insert on a table according to two fields (both foreign keys) on which I couldn't set a UNIQUE constraint (so INSERT ... ON DUPLICATE KEY UPDATE won't work). Here's what I ended up using:

replace into last_recogs (id, hasher_id, hash_id, last_recog) 
  select l.* from 
    (select id, hasher_id, hash_id, [new_value] from last_recogs 
     where hasher_id in (select id from hashers where name=[hasher_name])
     and hash_id in (select id from hashes where name=[hash_name]) 
     union 
     select 0, m.id, h.id, [new_value] 
     from hashers m cross join hashes h 
     where m.name=[hasher_name] 
     and h.name=[hash_name]) l 
  limit 1;

This example is cribbed from one of my databases, with the input parameters (two names and a number) replaced with [hasher_name], [hash_name], and [new_value]. The nested SELECT...LIMIT 1 pulls the first of either the existing record or a new record (last_recogs.id is an autoincrement primary key) and uses that as the value input into the REPLACE INTO.