update table while preserving the value of a column - php

Question

I have a scheduled job that will parse the following CSV file, and if the server is already in the table execute an update, insert if not. (The server name is the key).
The problem is that the CSV may contain lines with the same server but with a different application. In those cases, I must do an update, but keep the previous value of the app.
How can I keep the previous value before updating?
server_name;ip_address;domain;application
s1;10.10.10.4;dom1;app1
s1;10.10.10.4;dom1;app2
s2;10.15.69.8;dom5;app10
s3;10.15.69.39;dom7;app5
My code is like ($tab contains what I have on the table)
while(($line = fgetcsv($lines))!== false){
if (in_array($line[0],$tab)){ //update query}
else { //insert query }
}

Answer 1

You say this is a scheduled job. Because this is a repeating activity it would be worth your while to build some infrastructure: specifically an external table to provide a SQL interface for the CSV file.
External tables are highly neat: they are defined using CREATE TABLE but instead of a storage clause we specify a source file (pretty similar to SQL*Loader controlfile syntax). Then we can query the data in the CSV file without loading it into a staging table. Find out more.
As for the problem of inserting and updating you should check out the MERGE statement. This handles INSERT and UPDATE in a single statement. Note that you can drive the MERGE using an external table:
merge into your_table
using ( select * from external_table ) ext
on ( your_table.server_name = ext.server_name )
when not matched
then insert values ( ext.server_name, ....)
when matched
then update set your_table.ip_address = ext.ip_address ....
We can apply conditional filters to the INSERT and UPDATE clauses. Find out more.

Answer 2

Import you csv rows value in a temporary parking table and then use an insert select for the rows not in your final destination table
insert into your_final_dest (server_name,ip_address,domain,application)
select server_name,ip_address,domain,application
from your_csv_parking
where server_name not in ( select server_name from your_final_dest )
adn use update for others
UPDATE your_final_dest
SET application = (SELECT application
FROM your_csv_parking
WHERE your_final_dest.server = your_csv_parking.server)
WHERE EXISTS (SELECT your_csv_parking.application
FROM your_csv_parking
WHERE your_final_dest.server = your_csv_parking.server);