ThinkPHP5 is a lightweight PHP development framework, very suitable for rapid development of web applications. When developing using a framework, you often encounter situations where you need to query certain fields in the database. This article will introduce how to use ThinkPHP5 to query some fields.

1. Basic Query

First, let’s look at the most basic query example:

$user?=?Db::name('user')->where('id',?1)->find();

This query will return a user’s complete information, including All fields. But sometimes, we don't need to query all fields, but only some of them. At this time, we can use the select method to specify the fields to be queried:

$user?=?Db::name('user')->where('id',?1)->field('id,?name')->find();

This query only returns the values ??of the user's id and name fields, and other fields are ignored.

2. Query the fields of the related table

If you need to query the fields of a related table, we can also use the field method to specify the field to be queried. For example, we have a user table and an order table. There is a one-to-many relationship between them, that is, a user can have multiple orders. Now we want to query all the order numbers of a user:

$user?=?Db::name('user')->where('id',?1)->find();
$orders?=?Db::name('order')->where('user_id',?$user['id'])->field('order_no')->select();

Here we first query the user's complete information, and then query all his order numbers based on the user id, and specify that only order_no in the order table be queried field.

3. Query the results of aggregate functions

Sometimes we need to query the results of some aggregate functions, such as sum, average, maximum, minimum, etc. In ThinkPHP5, we can use the aggregate function in the query builder to achieve this. For example, we want to query the total amount of all orders in an order table:

$total_amount?=?Db::name('order')->sum('amount');

This query returns the total amount of all orders.

4. Convert the query results into an array

In the above example, the result we query through the select method is a two-dimensional array, each row represents a record, and each Column represents a field. If we only want the value of a certain column, we can use the column method to extract it. For example, we want to query the IDs of all users in the user table:

$ids?=?Db::name('user')->column('id');

This query returns a one-dimensional array that contains the IDs of all users.

5. Convert the query results to JSON format

Sometimes we need to convert the query results to JSON format so that they can be returned to the caller in the API interface. In ThinkPHP5, we can use the json method to convert query results into JSON format. For example:

$users?=?Db::name('user')->select();
return?json($users);

This code will convert the query results into JSON format and return them.

Summary

The above is how to use ThinkPHP5 to query some fields. We can use the field method to specify the field to be queried; use the aggregate function to query specific results; use the column method to extract a certain field of a row of data; use the json method to convert the query results into JSON format. Using these methods allows us to query the database more flexibly and improve development efficiency.

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