UPDATE/INSERT based on if a row exists - php

Question

Working on some postgreSQL queries. As I said in a previous question..my knowledge of SQL logic is quite limited..
I have this query that inserts a row.
$timestamp = date('Y-m-d G:i:s.u');
$check_time = "start"; //can also be stop
$check_type = "start_user"; //can also be stop_user
$insert_query = "INSERT INTO production_order_process_log (
production_order_id,
production_order_process_id,
$check_time,
$check_type)
VALUES (
'$production_order_id',
'$production_order_process_id',
'$timestamp',
'$user')
";
Unfortunately, that is adding a new row every time. I would like to add conditional SQL so that
if the production_order_process_id doesn't exist, do the INSERT as it's written in the query above. That is, add the new row with all the new information
but if the production_order_process_id does exist and the check_type is stop_user then UPDATE the row to fill the column stop with the $timestamp and fill the column stop_user with $user.
I understand this is complicated.. Or, at least for me it is ^^ Thanks much for the help!

Answer 1

This is usually called MERGE or upsert. PostgreSQL doesn't have explicit support for this operation.
The best article I've seen on the topic of MERGE in PostgreSQL is this one by depesz .

Answer 2

After insert type ON DUPLICATE KEY UPDATE...

Answer 3

Use MERGE statement
Here is the usage
MERGE INTO table [[AS] alias]
USING [table-ref | query]
ON join-condition
[WHEN MATCHED [AND condition] THEN MergeUpdate | DELETE]
[WHEN NOT MATCHED [AND condition] THEN MergeInsert]
MergeUpdate is
UPDATE SET { column = { expression | DEFAULT } |
( column [, ...] ) = ( { expression | DEFAULT } [, ...] ) }
[, ...]
(yes, there is no WHERE clause here)
MergeInsert is
INSERT [ ( column [, ...] ) ]
{ DEFAULT VALUES | VALUES ( { expression | DEFAULT } [, ...] )
[, ...]}
(no subquery allowed)
I'm sure you'll find more articles/examples if you search for it.

Answer 4

It would be good if you can create a stored procedure and call while insert new record.
DELIMITER $$
DROP PROCEDURE IF EXISTS `DB`.`InsertNewRow` $$
CREATE PROCEDURE `db`.`InsertNewRow` ()
BEGIN
DECLARE V_EXIST INT DEFAULT 0;
DECLARE V_check_type VARCHAR(20);
SELECT production_order_process_id,check_type INTO V_EXIST,V_check_type FROM production_order_process_log;
IF V_EXIST=0 THEN
INSERT INTO production_order_process_log (
production_order_id,
production_order_process_id,
$check_time,
$check_type)
VALUES (
'$production_order_id',
'$production_order_process_id',
'$timestamp',
'$user');
ELSEIF V_check_type='stop_user' THEN
/* UPDATE QUERY HERE */
END IF;
END $$
DELIMITER ;

Answer 5

Just ad a WHERE CLAUSE to the insert:
INSERT INTO production_order_process_log
( production_order_id, production_order_process_id, check_time, check_type)
VALUES ( '$production_order_id', '$production_order_process_id', '$timestamp', '$user')
WHERE NOT EXISTS ( SELECT *
FROM production_order_process_log nx
--
-- assuming production_order_id is the Primary Key, here
--
WHERE nx.production_order_id = '$production_order_id'
);
UPDATE: I was confused by the parameters and the VALUE() . The fragment below works without parameters, but
with immediate values:
INSERT INTO tmp.production_order_process_log
( production_order_id, production_order_process_id, check_time, check_type)
SELECT 1, 2, '2012-07-19 12:12:12', 'Lutser'
WHERE NOT EXISTS ( SELECT *
FROM tmp.production_order_process_log nx
--
-- assuming production_order_id is the Primary Key, here
--
WHERE nx.production_order_id = 1
);
(you'll have to change it a bit to re-add the parameters)