Detailed explanation of how thinkphp performs cross-table multi-condition query

When using ThinkPHP for database operations, it is often necessary to perform cross-table multi-condition queries. In this case, we need to use the query builder (Query Builder) provided by ThinkPHP to build the query statement. This article will introduce how to use ThinkPHP's query builder to perform cross-table multi-condition queries.

1. Master-slave table query

When performing cross-table query, we need to first determine which table is the master table and which table is the slave table. The master table is the table we want to query, and the slave table is the table we want to query. For example, we have two tables, one is the users table (users) and the other is the orders table (orders). If we want to query all the order information of this user, then the users table is the main table and the orders table is the slave table.

You can use join query to query the master-slave table using ThinkPHP. There are four types of join queries: left, right, inner, and full. Please understand the differences between these four join queries by yourself.

Sample code:

$users = Db::table('users')
        ->alias('u')
        ->join('orders o', 'o.user_id = u.id', 'left')
        ->select();

In the above sample code, we use the table method of the Db class to specify the main table, the alias method to set the alias of the table, and the join method to perform associations. Inquire. Among them, the first parameter is the table name of the slave table, the second parameter is the association condition of the two tables, and the third parameter is the join type.

2. Query across multiple slave tables

When performing cross-table queries, sometimes you need to associate multiple slave tables. In this case, you can use multiple join methods to associate.

Sample code:

$users = Db::table('users')
        ->alias('u')
        ->join('orders o', 'o.user_id = u.id', 'left')
        ->join('order_items oi', 'oi.order_id = o.id', 'left')
        ->select();

In the above example code, we used the join method twice, the first time to associate the order table, and the second time to associate the order item table. In this way, we can query all the user's order information and all line item information in each order.

3. Multi-condition query

When performing data query, sometimes more than one piece of data needs to be queried, and multiple conditions need to be used to determine the data that needs to be queried. At this time, you can use the where method to set multiple query conditions. Suppose we want to query the information of all users in the user table whose age is greater than 25 years old and whose gender is male. We can use the following code:

Sample code:

$users = Db::table('users')
        ->where('age', '>', 25)
        ->where('gender', 'male')
        ->select();

In the above example code, we use Use the where method twice to set the query conditions. The first parameter is the field name of the query condition, the second parameter is the comparison operator of the query condition, and the third parameter is the value of the query condition.

4. Cross-table multi-condition query

When performing cross-table query, we can combine the where method and join method to perform cross-table multi-condition query. For example, in the above example, we want to query all order information of all users who are older than 25 years old and male in the user table, we can use the following code:

Sample code:

$users = Db::table('users')
        ->alias('u')
        ->join('orders o', 'o.user_id = u.id', 'left')
        ->where('u.age', '>', 25)
        ->where('u.gender', 'male')
        ->select();

In the above example code, we add the alias of the table to which the query condition belongs in front of the query condition. In this way, cross-table multi-condition queries can be implemented.

When using ThinkPHP to perform cross-table multi-condition query, you need to pay attention to the following points:

1. You need to determine the main table and slave table first;
2. You need to use join method to perform associated queries;
3. You can use the join method to associate slave tables multiple times;
4. You can use the where method to set multiple query conditions.

In short, using ThinkPHP's query builder can easily implement cross-table multi-condition queries, helping us better complete database operations.

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