Check Data in MySQL row before Insert or Update

I would like to be able to check the data held in a row and then either insert or append if BOTH values exist to an already existing value, how can I do this?

The values I would like to check are Lat and Lon and both would be checked, if they are the same as the sent data then the Description is appended otherwise add a new row:

Table Layout e.g.:
ID(Unique) | Lat | Lon | Description | Date
1            0.1   0.1   Test          some date

Data being sent: 
Lat: 0.1, Lon: 0.1, Description: Test2

I would therefore like the table to end up like this:
ID(Unique) | Lat | Lon | Description | Date
1            0.1   0.1 **Test, Test2** some date

More data being sent:
Lat: 0.2, Lon: 0.1, Description: Test3

After:
ID(Unique) | Lat | Lon |开发者_StackOverflow社区 Description | Date
1            0.1   0.1   Test, Test2   some date
2            0.2   0.1   Test3         some date

I have been looking at UPDATE but I cant seem to get the correct syntax:

If you set Lat and Lon as a compound unique key you can use INSERT...ON DUPLICATE KEY UPDATE syntax.

INSERT INTO tableName (Lat, Lon, Description, Date) VALUES 
(0.1, 0.1, 'Test 2', NOW()) 
ON DUPLICATE KEY UPDATE 
Description = CONCAT(Description, ', Test2')

This has the disadvantage of being non-ANSI (and therefore not portable) SQL.

Rarely is what you're trying to do the correct answer. Normalization is.

Typically you'd create a relation table that looked like:

ID    |   Description(unique)

And store all the descriptions there.

Take a look at this

http://dev.mysql.com/doc/refman/5.0/en/insert-on-duplicate.html

and use concat() function to append text.