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For developers using PHP, a common scenario is the need to jointly query data from the databases of two different servers. This scenario may be due to business needs or because the data is distributed on different servers. This article will introduce how to complete this data federation query operation in PHP.
Before we start writing code, we need to determine the data we want to query. Suppose we have two database services, named A and B. We need to jointly query customer information from these two databases, including customer ID, name, age, and gender. Both databases A and B have customer tables, which are customers_a
and customers_b
respectively. These tables include basic information about customers.
Our query goal is to obtain the information of all customers in customers_a
and customers_b
, so we need to perform JOIN operations on the two tables.
It is easy to connect two databases using PHP. The following is a code example to connect to database A:
<?php $host = 'localhost'; $username = 'db_user'; $password = 'db_password'; $dbname = 'database_a'; $db_a = new mysqli($host, $username, $password, $dbname); if ($db_a->connect_error) { die('Connect Error (' . $db_a->connect_errno . ') ' . $db_a->connect_error); }
Similarly, we can connect to database B:
<?php $host = 'localhost'; $username = 'db_user'; $password = 'db_password'; $dbname = 'database_b'; $db_b = new mysqli($host, $username, $password, $dbname); if ($db_b->connect_error) { die('Connect Error (' . $db_b->connect_errno . ') ' . $db_b->connect_error); }
Now we have successfully connected to two different databases.
Next, we need to perform a JOIN operation on the two databases to obtain the data we need. In order to ensure the readability and maintainability of the code, we encapsulate the query operation into a function.
<?php function get_customers($db_a, $db_b) { $sql = "SELECT id, name, age, gender FROM customers_a UNION SELECT id, name, age, gender FROM customers_b"; $result = $db_a->query($sql); if (!$result) { die('Query Error: ' . $db_a->error); } $rows = array(); while ($row = $result->fetch_assoc()) { $rows[] = $row; } $result->free(); return $rows; }
In this function, we use the UNION operation to merge the data in customers_a
and customers_b
together. After executing the query, we put the records in the result set into an array and return the array.
Now we have completed all the code writing work. We can call the get_customers
function in the code to obtain the customer information jointly queried from the two databases A and B.
<?php $rows = get_customers($db_a, $db_b); foreach ($rows as $row) { echo $row['id'] . ' ' . $row['name'] . ' ' . $row['age'] . ' ' . $row['gender'] . '<br>'; }
The following is the complete code example:
<?php $host_a = 'localhost'; $username_a = 'db_user'; $password_a = 'db_password'; $dbname_a = 'database_a'; $host_b = 'localhost'; $username_b = 'db_user'; $password_b = 'db_password'; $dbname_b = 'database_b'; $db_a = new mysqli($host_a, $username_a, $password_a, $dbname_a); if ($db_a->connect_error) { die('Connect Error (' . $db_a->connect_errno . ') ' . $db_a->connect_error); } $db_b = new mysqli($host_b, $username_b, $password_b, $dbname_b); if ($db_b->connect_error) { die('Connect Error (' . $db_b->connect_errno . ') ' . $db_b->connect_error); } function get_customers($db_a, $db_b) { $sql = "SELECT id, name, age, gender FROM customers_a UNION SELECT id, name, age, gender FROM customers_b"; $result = $db_a->query($sql); if (!$result) { die('Query Error: ' . $db_a->error); } $rows = array(); while ($row = $result->fetch_assoc()) { $rows[] = $row; } $result->free(); return $rows; } $rows = get_customers($db_a, $db_b); foreach ($rows as $row) { echo $row['id'] . ' ' . $row['name'] . ' ' . $row['age'] . ' ' . $row['gender'] . '<br>'; } $db_a->close(); $db_b->close(); ?>
In PHP, connect two different databases And performing joint query operations is a very common scenario. This article describes how to connect two different database services in PHP and use the UNION operation to complete the joint query task. Through this article, we hope readers can better understand how to use multiple database services in PHP.
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