Let's talk about some joint table query methods in php+mysql without join

In the process of joint use of PHP and MySQL, it is very important to understand how to use join table query. However, as we know, joins make query execution less efficient.

So, is there a way to perform joint table queries without using join? The answer is yes! In this article, we will introduce some joint table query methods that do not use join, and compare their differences with using join.

1. Using subqueries

A subquery is a query statement that is nested within another query statement. The result set of the subquery will be processed as part of the main query statement.

In a joint table query, we can use a subquery to query data in another table. For example, if we want to query the value of a field from one table, but this value is a field of another table, we can use a subquery to achieve this.

For example, we have two tables: users and orders. User information is stored in the users table, and order information is stored in the orders table. We want to find the user's address, but the address is stored in the orders table. We can use the following query:

SELECT address FROM orders WHERE user_id = (SELECT id FROM users WHERE username = 'Bob');

Here, we use a subquery to get the user's id, which was then used in the main query to find the user's address.

2. Using associative arrays

In PHP, we can simulate a joint table query by storing the data of two tables in two associative arrays. For example, we have two arrays: $users and $orders. We can concatenate two arrays through the following code:

foreach ($orders as $order) {

$user_id = $order['user_id'];
$users[$user_id]['address'] = $order['address'];

}

Here, we iterate over the $orders array and Use $user_id to get the corresponding user record. We then use that user id to store the order's address in the $users array. Ultimately, the $users array will contain the users' information, as well as their addresses.

3. Using substrings and LIKE statements

In some cases, you can use substrings and LIKE statements to join data from two tables. For example, we have two tables: users and orders. There is a field named email in the users table, and there is a field named email_domain in the orders table. We want to join records from two tables by using the following query:

SELECT u., o. FROM users u, orders o WHERE u.email LIKE CONCAT( '%', o.email_domain);

In this query, we use the LIKE operator and CONCAT function. The LIKE operator is used to fuzzy match text, while the CONCAT function concatenates strings. We used the LIKE operator and CONCAT function in the query to join the data from the two tables.

Summary

In PHP and MySQL, join table query is a very common operation. However, join will reduce query efficiency. Therefore, we introduced three methods of joining tables without using joins: using subqueries, using associative arrays, and using substrings and LIKE statements. These methods may not be as efficient as join, but they can be very useful in certain situations. Depending on the specific situation, we have the flexibility to choose which method to use.

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