How to perform multi-table link query in thinkphp

To learn to perform multi-table link queries in ThinkPHP, you first need to master the basic syntax. In ThinkPHP, you can perform multi-table link queries in the following ways:

Db::table('table1')
    ->alias('t1')
    ->join('table2 t2', 't1.id = t2.table1_id')
    ->join('table3 t3', 't1.id = t3.table1_id')
    ->where('t1.id', $id)
    ->select();

In the above statement, we perform multi-table links through the join method, where the first parameter is the link to be The table name, the second parameter is the link condition. We can use the alias alias to add an alias to the table to facilitate subsequent operations.

In the where method, we can specify the conditions that need to be filtered. In this example, we use t1.id to filter the records whose id field is equal to $id in the t1 table.

We may need to perform more complex connection queries to integrate data from multiple tables for statistical analysis. At this time, we can use the aggregate function provided by ThinkPHP to perform calculations.

For example, if we want to count the number of orders for each user, we can use the following statement to query:

Db::table('user')
    ->alias('u')
    ->join('order o', 'u.id = o.user_id')
    ->field('u.*, COUNT(o.id) as order_num')
    ->group('u.id')
    ->select();

In the above statement, we used the COUNT function to count orderThe order quantity of each user in the table, and use the group method to group the results according to u.id.

In addition, we can also use HAVING conditions for further filtering. For example, if we want to filter out users whose order quantity is greater than or equal to 5, we can use the following statement:

Db::table('user')
    ->alias('u')
    ->join('order o', 'u.id = o.user_id')
    ->field('u.*, COUNT(o.id) as order_num')
    ->group('u.id')
    ->having('order_num >= 5')
    ->select();

In the above statement, we use the HAVING condition to filter out users whose order quantity is greater than or equal to 5 User.

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