Let's look at a typical situation. Imagine you’ve got one table:

CREATE TABLE PUBLIC.TBUPSERTEXAMPLE
(
    KEY1 CHARACTER VARYING(10) NOT NULL,
    KEY2 CHARACTER VARYING(14) NOT NULL,
    KEY3 CHARACTER VARYING(14) NOT NULL,
    KEY4 CHARACTER VARYING(14) NOT NULL,

    VALUE1 CHARACTER VARYING(20),
    VALUE2 CHARACTER VARYING(20) NOT NULL,
    VALUE3 CHARACTER VARYING(100),
    VALUE4 CHARACTER VARYING(400),
    VALUE5 CHARACTER VARYING(20),

    CONSTRAINT TBUPSERTEXAMPLE_PKEY PRIMARY KEY (KEY1, KEY2, KEY3, KEY4)
)

And you need to update one record. You can perform a simple UPDATE statement, but what happens the first time?

You cannot update the record because the record doesn’t exist. You need to create an INSERT statement instead. We can do it the following different ways. You can first create a SELECT statement and, if the record exists, perform an UPDATE. If it doesn’t exist, you perform an INSERT. We also can perform an UPDATE and see how many records are affected. If no records are affected, then we perform an INSERT. Finally, we can perform one INSERT, and if it throws an error, then perform an UPDATE.

All of these techniques works in one way or another, but PostgreSQL gives us one cool way of doing this operation with one SQL sentence. We can use CTE (Common Table Expression) and execute something like this:

WITH upsert AS (
    UPDATE PUBLIC.TBUPSERTEXAMPLE
    SET
        VALUE1 = :VALUE1,
        VALUE2 = :VALUE2,
        VALUE3 = :VALUE3,
        VALUE4 = :VALUE4,
        VALUE5 = :VALUE5
    WHERE
        KEY1 = :KEY1 AND
        KEY2 = :KEY2 AND
        KEY3 = :KEY3 AND
        KEY4 = :KEY4
    RETURNING *
)
INSERT INTO PUBLIC.TBUPSERTEXAMPLE(KEY1, KEY2, KEY3, KEY4, VALUE1, VALUE2, VALUE3, VALUE4, VALUE5)
SELECT
    :KEY1, :KEY2, :KEY3, :KEY4, :VALUE1, :VALUE2, :VALUE3, :VALUE4, :VALUE5
WHERE
    NOT EXISTS (SELECT 1 FROM upsert);

Since PostgreSQL 9.5, we also can use another technique to do these UPSERT operations. We can do something like:

INSERT INTO PUBLIC.TBUPSERTEXAMPLE (key1, key2, key3, key4, value1, value2, value3, value4, value5)
    VALUES ('key2', 'key2', 'key3', 'key4', 'value1',  'value2',  'value3',  'value4',  'value5')
ON CONFLICT (key1, key2, key3, key4)
DO UPDATE SET 
    value1 = 'value1', 
    value2 = 'value2', 
    value3 = 'value3', 
    value4 = 'value4', 
    value5 = 'value5'
WHERE 
    TBUPSERTEXAMPLE.key1 = 'key2' AND 
    TBUPSERTEXAMPLE.key2 = 'key2' AND 
    TBUPSERTEXAMPLE.key3 = 'key3' AND 
    TBUPSERTEXAMPLE.key4 = 'key4';

To help me out, I’ve created a simple PHP wrapper.

Here's one example using PDO

use G\SqlUtils\Upsert;

$conn = new PDO('pgsql:dbname=gonzalo;host=localhost', 'username', 'password');
$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

$conn->beginTransaction();
try {
    Upsert::createFromPDO($conn)->exec('PUBLIC.TBUPSERTEXAMPLE', [
        'KEY1' => 'key1',
        'KEY2' => 'key2',
        'KEY3' => 'key3',
        'KEY4' => 'key4',
    ], [
        'VALUE1' => 'value1',
        'VALUE2' => 'value2',
        'VALUE3' => 'value3',
        'VALUE4' => 'value4',
        'VALUE5' => 'value5',
    ]);
    $conn->commit();
} catch (Exception $e) {
    $conn->rollback();
    throw $e;
}

And another one using DBAL:

use Doctrine\DBAL\DriverManager;
use G\SqlUtils\Upsert;

$connectionParams = [
    'dbname'   => 'gonzalo',
    'user'     => 'username',
    'password' => 'password',
    'host'     => 'localhost',
    'driver'   => 'pdo_pgsql',
];

$dbh = DriverManager::getConnection($connectionParams);
$dbh->transactional(function ($conn) {
    Upsert::createFromDBAL($conn)->exec('PUBLIC.TBUPSERTEXAMPLE', [
        'KEY1' => 'key1',
        'KEY2' => 'key2',
        'KEY3' => 'key3',
        'KEY4' => 'key4',
    ], [
        'VALUE1' => 'value1',
        'VALUE2' => 'value2',
        'VALUE3' => 'value3',
        'VALUE4' => null,
        'VALUE5' => 'value5',
    ]);
});

And that’s all! For more information, the library is available in my GitHub, and it’s also at Packagist.