How thinkphp implements query between two tables

When developing web applications, it is often necessary to query data from multiple tables, and thinkphp is a very popular and convenient PHP framework that supports a variety of database operations. This article will introduce how to use thinkphp to query two tables.

Step one: Get the database object

In thinkphp, we can get the database object through the following code:

$db = \think\Db::connect();

If the database configuration has been set up, you can directly Use \think\Db::name('table name') to obtain the object that operates a database table.

Second step: joint table query

In thinkphp, use the join() method to implement joint table query.

For example, we have two tables user and order, which have the same user ID. We need to query the user's name, order number and other information. The following is the query code:

$data = \think\Db::name('user')
    ->join('order', 'user.id = order.user_id')
    ->field('user.name, order.order_no')
    ->select();

join method accepts two parameters, the first parameter is the name of the table to be joined, and the second parameter is the association condition. In the above example, we use the user table as the main table, the order table as the joined table, and the association condition is user.id = order.user_id. The

field method can specify the fields to be queried, which can avoid unnecessary fields and improve query efficiency.

Finally call the select method to perform the query operation and return the result set.

Step Three: Left Join Query

Left join query is also a commonly used join table query method. It can query all data in the master table and merge the corresponding slave table data together according to the association conditions.

The following is an example of a left join query:

$data = \think\Db::name('user')
    ->alias('u')
    ->join('order o', 'u.id = o.user_id', 'LEFT')
    ->field('u.*, o.order_no')
    ->select();

Among them, the alias method is used to set aliases for the main table, which is easy to manage and query. The third parameter of the join method sets the join table type, here it is a left join query. Among the parameters of the last field method, u.* means querying all fields of the user table, and o.order_no means querying the order number field of the order table.

Step 4: Native SQL query

In some cases, flexible use of native SQL statements can be more convenient and faster. thinkphp also supports native SQL queries, just call the query method.

The following is an example of a native SQL query:

$sql = "SELECT u.name, o.order_no FROM `user` u LEFT JOIN `order` o ON u.id = o.user_id WHERE u.status = 1";

$data = \think\Db::query($sql);

In the above example, we used a native SQL statement to connect the two tables and added a WHEREFilter conditions to query all users with status 1 and their order numbers.

Summary

In thinkphp, join table query can be implemented using the join() method. Left join query can be implemented by setting the join table type, or you can use native SQL statement query. Reasonable and flexible use of these methods can make queries faster and more efficient.

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