Query builder in Yii framework: Simplifying database operations

With the development and popularity of Web applications, data processing has become more and more important. The database is the core of data processing. This article will introduce the query builder in the Yii framework. It is a powerful tool that can simplify database operations and improve development efficiency.

Yii framework is a high-performance PHP framework based on MVC pattern. It provides many features and components, one of the most important components is the query builder (QueryBuilder). Query builders allow us to interact with the database in a more elegant way, using an object-oriented approach.

Different from traditional SQL statements, the query builder uses an object-oriented approach to construct SQL statements. We use PHP code to represent the queries we want to make, and the query builder is responsible for converting these codes into corresponding SQL statements.

The following are some common methods of query builder in Yii framework.

1. select()

The select() method is used to set which columns to select. If we need to select all columns, we can use * as parameter. An example is as follows:

$query = Yii::$app->db->createCommand()->select('*')->from('users');

If we only need to select certain columns, we can pass the column name as a parameter to the select() method, and multiple column names can be passed using an array. An example is as follows:

$query = Yii::$app->db->createCommand()->select(['id', 'username'])->from('users');

2. from()

from() method is used to set the query data table. Examples are as follows:

$query = Yii::$app->db->createCommand()->select('*')->from('users');

3. where()

where() method is used to set query conditions. An example is as follows:

$query = Yii::$app->db->createCommand()->select('*')->from('users')->where(['status' => 1]);

Among them, status is the column name, and 1 is the value of the column.

In addition to using key-value pairs, we can also use arrays to pass the relationship between the conditions of multiple query conditions. The default is "AND" relationship. An example is as follows:

$query = Yii::$app->db->createCommand()->select('*')->from('users')->where(['status' => 1, 'age' => 18]);

This will generate the following SQL statement:

SELECT * FROM `users` WHERE `status`=:status AND `age`=:age

If we need to use the "OR" relationship, we can write like this:

$query = Yii::$app->db->createCommand()->select('*')->from('users')->where(['or', ['status' => 1], ['age' => 18]]);

This will generate the following SQL statement :

SELECT * FROM `users` WHERE (`status`=:status OR `age`=:age)

4. limit() and offset()

#limit() method is used to set the maximum number of rows returned by query results, and offset() method is used to set the query The offset of the result. An example is as follows:

$query = Yii::$app->db->createCommand()->select('*')->from('users')->where(['status' => 1])->limit(10)->offset(5);

This will generate the following SQL statement:

SELECT * FROM `users` WHERE `status`=:status LIMIT 10 OFFSET 5

5. orderBy()

The orderBy() method is used to sort the results. An example is as follows:

$query = Yii::$app->db->createCommand()->select('*')->from('users')->where(['status' => 1])->orderBy('age');

This will generate the following SQL statement:

SELECT * FROM `users` WHERE `status`=:status ORDER BY `age`

6. groupBy() and having()

The groupBy() method is used to The results are grouped, and the having() method is used to set the grouping conditions. An example is as follows:

$query = Yii::$app->db->createCommand()->select('count(*) as cnt, status')->from('users')->groupBy('status')->having(['>', 'cnt', 10]);

This will generate the following SQL statement:

SELECT count(*) as cnt, status FROM `users` GROUP BY `status` HAVING cnt > 10

The query builder allows us to interact with the database in an object-oriented manner in a more elegant way. When using the Yii framework to develop web applications, we can make full use of the query builder to simplify database operations and improve development efficiency.

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