Phalcon查询语言(Phalcon Query Language)

Phalcon查询语言，简称PhalconQL或PHQL，是一种面向对象的高级SQL语言，允许用标准化的SQL编写。PHQL实现了把操作语句解析为RDBMS目标语言的解析器(C语言编写)。

为了达到最佳性能，Phalcon提供了与SQLite相同的解析器，其线程安全，内存占用极低。

解析器先检查传递的PHQL语句的语法，然后构建中间语句，最后将其转换为RDBMS对应的SQL语句。

PHQL实现了一系列功能，可以更安全的操作数据库。

参数绑定是PHQL功能之一，使代码更安全

PHQL每次只允许执行一条SQL语句，以防SQL注入

PHQL会忽略所有SQL注入中常用的SQL注释

PHQL只允许数据操作语句，避免错误的或未经授权的更改、删除数据库和表

PHQL实现了高级抽象接口，允许以模型方式操作表，以类属性方式操作表字段

使用示例(Usage Example)

为了更好的解释PHQL工作原理，请参考下例。有Cars和Brands两个模型：

use Phalcon\Mvc\Model;

class Cars extends Model

{

public $id;

public $name;

public $brand_id;

public $price;

public $year;

public $style;

// 模型Cars映射sample_cars表

public function getSource()

{

return 'sample_cars';

}

// 一辆车属于一个品牌，但一个品牌有多辆车

public function initialize()

{

$this->belongsTo('brand_id', 'Brands', 'id');

}

}

每辆车都属于一个品牌，每个品牌有多辆车：

use Phalcon\Mvc\Model;

class Brands extends Model

{

public $id;

public $name;

// 模型Brands映射表'sample_brands'

public function getSource()

{

return 'sample_brands';

}

// 一个品牌有多辆车

public function initialize()

{

$this->hasMany('id', 'Cars', 'brand_id');

}

}

创建PHQL查询(Creating PHQL Queries)

实例化Phalcon\Mvc\Model\Query类即可创建PHQL查询：

use Phalcon\Mvc\Model\Query;

// 实例化Query

$query = new Query(

"SELECT * FROM Cars",

$this->getDI()

);

// 执行查询，返回结果(如果有的话)

$cars = $query->execute();

控制器或视图中，使用Phalcon\Mvc\Model\Manager可以很容易的创建、执行PHQL查询：

// 执行简单查询

$query = $this->modelsManager->createQuery("SELECT * FROM Cars");

$cars = $query->execute();

// 使用参数绑定

$query = $this->modelsManager->createQuery("SELECT * FROM Cars WHERE name = :name:");

$cars = $query->execute(

[

'name' => 'Audi',

]

);

或者直接执行查询：

// 执行简单查询

$cars = $this->modelsManager->executeQuery(

"SELECT * FROM Cars"

);

// 使用参数绑定

$cars = $this->modelsManager->executeQuery(

"SELECT * FROM Cars WHERE name = :name:",

[

'name' => 'Audi',

]

);

查询记录(Selecting Records)

PHQL允许使用我们熟知的SELECT语句查询记录，使用模型名字代替表名：

$query = $manager->createQuery(

"SELECT * FROM Cars ORDER BY Cars.name"

);

$query = $manager->createQuery(

"SELECT Cars.name FROM Cars ORDER BY Cars.name"

);

允许带命名空间的模型名：

$phql = "SELECT * FROM Formula\Cars ORDER BY Formula\Cars.name";

$query = $manager->createQuery($phql);

$phql = "SELECT Formula\Cars.name FROM Formula\Cars ORDER BY Formula\Cars.name";

$query = $manager->createQuery($phql);

$phql = "SELECT c.name FROM Formula\Cars c ORDER BY c.name";

$query = $manager->createQuery($phql);

PHQL支持大部分标准SQL语法，非标准的SQL语法也同样支持，如LIMIT：

$phql = "SELECT c.name FROM Cars AS c WHERE c.brand_id = 21 ORDER BY c.name LIMIT 100";

$query = $manager->createQuery($phql);

结果集类型(Result Types)

结果集类型根据我们查询字段的不同而不同，如果检索单个完整对象，则返回Phalcon\Mvc\Model\Resultset\Simple对象。这种结果集是一组完整的模型对象：

$phql = "SELECT c.* FROM Cars AS c ORDER BY c.name";

$cars = $manager->executeQuery($phql);

foreach ($cars as $car) {

echo 'Name: ', $car->name, "\n";

}

下面这种方式也一样：

$cars = Cars::find(

[

'order' => 'name',

]

);

foreach ($cars as $car) {

echo 'Name: ', $car->name, "\n";

}

完整模型对象中的数据能够被修改，并重新保存到数据库中，因为它们代表关联表的完整记录。下面这种查询方式不会返回完整模型对象：

$phql = "SELECT c.id, c.name FROM Cars AS c ORDER BY c.name";

$cars = $manager->executeQuery($phql);

foreach ($cars as $car) {

echo 'Name: ', $car->name, "\n";

}

我们仅仅查询了表中的某些字段，虽然返回的结果集仍然是Phalcon\Mvc\Model\Resultset\Simple对象，但不能当成完整模型对象。该对象的每个成员都是一个包含所查询字段的标准对象。

这些不表示完整对象的值就是我们所说的标量，PHQL允许查询所有类型的标量：字段，函数，字面两，表达式等：

$phql = "SELECT CONCAT(c.id, ' ', c.name) AS id_name FROM Cars AS c ORDER BY c.name";

$cars = $manager->execute($phql);

foreach ($cars as $car) {

echo $car->id_name, "\n";

}

我们可以查询完整对象或标量，也可以同时查询它们：

$phql = "SELECT c.price*0.16 AS taxes, c.* FROM Cars AS c ORDER BY c.name";

$result = $manager->executeQuery($phql);

这种情况下的结果集是一个Phalcon\Mvc\Model\Resultset\Complex对象，可以同时访问完整对象和标量：

foreach ($result as $row) {

echo 'Name: ', $row->cars->name, "\n";

echo 'Price: ', $row->cars->price, "\n";

echo 'Taxes: ', $row->taxes, "\n";

}

连接(Joins)

使用PHQL可以很容易的从多个模型请求记录，支持大部分的JOIN方式。我们在模型中定义关系之后，PHQL会自动添加这些条件：

$phql = "SELECT Cars.name AS car_name, Brands.name AS brand_name FROM Cars JOIN Brands";

$rows = $manager->executeQuery($phql);

foreach ($rows as $row) {

echo $row->car_name, "\n";

echo $row->brand_name, "\n";

}

默认使用INNER JOIN，可以指定JOIN类型：

$phql = "SELECT Cars.*, Brands.* FROM Cars INNER JOIN Brands";

$rows = $manager->executeQuery($phql);

$phql = "SELECT Cars.*, Brands.* FROM Cars LEFT JOIN Brands";

$rows = $manager->executeQuery($phql);

$phql = "SELECT Cars.*, Brands.* FROM Cars LEFT OUTER JOIN Brands";

$rows = $manager->executeQuery($phql);

$phql = "SELECT Cars.*, Brands.* FROM Cars CROSS JOIN Brands";

$rows = $manager->executeQuery($phql);

也可以手动设置JOIN条件：

$phql = "SELECT Cars.*, Brands.* FROM Cars INNER JOIN Brands ON Brands.id = Cars.brands_id";

$rows = $manager->executeQuery($phql);

如果查询中为模型定义别名，则将使用别名为结果集中的每一条记录命名：

$phql = "SELECT c.*, b.* FROM Cars c, Brands b WHERE b.id = c.brands_id";

$rows = $manager->executeQuery($phql);

foreach ($rows as $row) {

echo 'Car: ', $row->c->name, "\n";

echo 'Brand: ', $row->b->name, "\n";

}

如果连接模型与from之后的模型具有多对多关系时，中间模型将隐式的添加到查询中：

$phql = "SELECT Artists.name, Songs.name FROM Artists JOIN Songs WHERE Artists.genre = 'Trip-Hop'";

$result = $this->modelsManager->executeQuery($phql);

上述代码在MySQL中执行下列SQL：

SELECT `artists`.`name`, `songs`.`name` FROM `artists`

INNER JOIN `albums` ON `albums`.`artists_id` = `artists`.`id`

INNER JOIN 'songs' ON `albums`.`songs_id` = `songs`.`id`

WHERE `artists`.`genre` = 'Trip-Hop'

聚合(Aggregations)

下面例子展示了PHQL中如何使用聚合：

// 所有汽车的总价值

$phql = "SELECT SUM(price) AS summatory FROM Cars";

$row = $manager->executeQuery($phql)->getFirst();

echo $row['summatory'];

// 每个品牌下的汽车总数

$phql = "SELECT Cars.brand_id, COUNT(*) FROM Cars GROUP BY Cars.brand_id";

$rows = $manager->executeQuery($phql);

foreach ($rows as $row) {

echo $row->brand_id, ' ', $row['1'], "\n";

}

// 每个品牌下的汽车总数

$phql = "SELECT Brands.name, COUNT(*) FROM Cars JOIN Brands GROUP BY 1";

$rows = $manager->executeQuery($phql);

foreach ($rows as $row) {

echo $row->name, ' ', $row['1'], "\n";

}

$phql = "SELECT MAX(price) AS maximum, MIN(price) AS minimum FROM Cars";

$rows = $manager->executeQuery($phql);

foreach ($rows as $row) {

echo $row['maximum'], ' ', $row['minimum'], "\n";

}

// 统计品牌数量

$phql = "SELECT COUNT(DISTINCT brand_id) AS brandId FROM Cars";

$rows = $manager->executeQuery($phql);

foreach ($rows as $row) {

echo $row->brandId, "\n";

}

条件(Conditions)

条件能让我们过滤想要查询的记录，WHERE子句允许这样:

// 简单条件

$phql = "SELECT * FROM Cars WHERE Cars.name = 'Lamborghini Espada'";

$cars = $manager->executeQuery($phql);

$phql = "SELECT * FROM Cars WHERE Cars.price > 10000";

$cars = $manager->executeQuery($phql);

$phql = "SELECT * FROM Cars WHERE TRIM(Cars.name) = 'Audi R8'";

$cars = $manager->executeQuery($phql);

$phql = "SELECT * FROM Cars WHERE Cars.name LIKE 'Ferrari%'";

$cars = $manager->executeQuery($phql);

$phql = "SELECT * FROM Cars WHERE Cars.name NOT LIKE 'Ferrari%'";

$cars = $manager->executeQuery($phql);

$phql = "SELECT * FROM Cars WHERE Cars.price IS NULL";

$cars = $manager->executeQuery($phql);

$phql = "SELECT * FROM Cars WHERE Cars.id IN (120, 121, 122)";

$cars = $manager->executeQuery($phql);

$phql = "SELECT * FROM Cars WHERE Cars.id NOT IN(430, 431)";

$cars = $manager->executeQuery($phql);

$phql = "SELECT * FROM Cars WHERE Cars.id BETWEEN 1 AND 100";

$cars = $manager->executeQuery($phql);

此外，作为PHQL的一部分，参数绑定会自动转义输入数据，安全性更高：

$phql = "SELECT * FROM Cars WHERE Cars.name = :name:";

$cars = $manager->executeQuery(

$phql,

[

'name' => 'Lamborghini Espada',

]

);

$phql = "SELECT * FROM Cars WHERE Cars.name = ?0";

$cars = $manager->executeQuery(

$phql,

[

0 => 'Lamborghini Espada',

]

);

插入数据(Inserting Data)

通过PHQL，可以使用我们非常熟悉的INSERT语句插入数据：

// 插入数据，不指定字段

$phql = "INSERT INTO Cars VALUES (NULL, 'Lamborghini Espada', 7, 10000.00, 1969, 'Grand Tourer')";

$manager->executeQuery($phql);

// 插入数据，指定字段

$phql = "INSERT INTO Cars (name, brand_id, year, style) VALUES ('Lamborghini Espada', 7, 1969, 'Grand Tourer')";

$manager->executeQuery($phql);

// 插入数据，使用占位符

$phql = "INSERT INTO Cars (name, brand_id, year, style) VALUES (:name:, :brand_id:, :year:, :style:)";

$manager->executeQuery(

$phql,

[

'name' => 'Lamborghini Espada',

'brand_id' => 7,

'year' => 1969,

'style' => 'Grand Tourer',

]

);

Phalcon不只是单纯的将PHQL语句转化成SQL，模型中定义的所有事件和业务规则都会执行，就像我们手动创建对象那样。我们为模型Cars创建一条规则，车的价格不能低于$ 10,000：

use Phalcon\Mvc\Model;

use Phalcon\Mvc\Model\Message;

class Cars extends Model

{

public function beforeCreate()

{

if ($this->price < 10000) {

$this->appendMessage(

new Message('A car cannot cost less than $ 10,000')

);

return false;

}

}

}

如果我们在模型Cars中执行下面的INSERT语句，操作将会失败，因为price不满足我们制定的规则。通过检查插入状态，我们可以打印任何内部生成的验证消息：

$phql = "INSERT INTO Cars VALUES (NULL, 'Nissan Versa', 7, 9999.00, 2015, 'Sedan')";

$result = $manager->executeQuery($phql);

if ($result->success() === false) {

foreach ($result->getMessages() as $message) {

echo $message->getMessage();

}

}

更新数据(Updating Data)

更新记录与插入记录非常相似，更新记录使用UPDATE命令。更新记录时，将为每条记录执行与更新操作相关的事件。

// 更新一个字段

$phql = "UPDATE Cars SET price = 15000.00 WHERE id = 101";

$manager->executeQuery($phql);

// 更新多个字段

$phql = "UPDATE Cars SET price = 15000.00, type = 'Sedan' WHERE id = 101";

$manager->executeQuery($phql);

// 更新多条记录

$phql = "UPDATE Cars SET price = 7000.00, type = 'Sedan' WHERE brands_id > 5";

$manager->executeQuery($phql);

// 使用占位符

$phql = "UPDATE Cars SET price = ?0, type = ?1 WHERE brands_id > ?2";

$manager->executeQuery(

$phql,

[

0 => 7000.00,

1 => 'Sedan',

2 => 5,

]

);

UPDATE语句执行更新分两步进行：

首先，如果UPDATE包含WHERE子句，将检索符合条件的所有对象

其次，基于查询对象更新字段并保存

这种操作方式允许事件、虚拟外键和验证参与更新过程。

$phql = "UPDATE Cars SET price = 15000.00 WHERE id > 101";

$result = $manager->executeQuery($phql);

if ($result->success() === false) {

$messages = $result->getMessages();

foreach ($messages as $message) {

echo $message->getMessage();

}

}

上面代码相当于：

$messages = null;

$process = function () use (&$messages) {

$cars = Cars::find('id > 101');

foreach ($cars as $car) {

$car->price = 15000;

if ($car->save() === false) {

$messages = $car->getMessages();

return false;

}

}

return true;

};

$success = $process();

删除数据(Deleting Data)

删除记录时，与删除操作相关的事件将逐一执行：

// 删除一条记录

$phql = "DELETE FROM Cars WHERE id = 101";

$manager->executeQuery($phql);

// 删除多条记录

$phql = "DELETE FROM Cars WHERE id > 100";

$manager->executeQuery($phql);

// 使用占位符

$phql = "DELETE FROM Cars WHERE id BETWEEN :initial: AND :final:";

$manager->executeQuery(

$phql,

[

'initial' => 1,

'final' => 100,

]

);

和UPDATE一样，DELETE操作也分两步执行，要检查删除操作是否产生验证消息，你可以检查返回的状态：

// 删除多条记录

$phql = "DELETE FROM Cars WHERE id > 100";

$result = $manager->executeQuery($phql);

if ($result->success() === false) {

$messages = $result->getMessages();

foreach ($messages as $message) {

echo $message->getMessage();

}

}

使用查询构造器创建查询(Creating queries using the Query Builder)

查询构造器可用于创建PHQL查询，无需编写PHQL语句：

// 获取所有记录

$robots = $this->modelsManager->createBuilder()

->from('Robots')

->join('RobotsParts')

->orderBy('Robots.name')

->getQuery()

->execute();

// 获取第一条记录

$robots = $this->modelsManager->createBuilder()

->from('Robots')

->join('RobotsParts')

->orderBy('Robots.name')

->getQuery()

->getSingleResult();

同下列操作：

$phql = "SELECT Robots.* FROM Robots JOIN RobotsParts p ORDER BY Robots.name LIMIT 20";

$result = $manager->executeQuery($phql);

查询构造器更多示例：

// "SELECT Robots.* FROM Robots";

$builder->from('Robots');

// "SELECT Robots.*, RobotsParts.* FROM Robots, RobotsParts";

$builder->from(

[

'Robots',

'RobotsParts',

]

);

// "SELECT * FROM Robots";

$phql = $builder->columns('*')

->from('Robots');

// "SELECT id FROM Robots";

$builder->columns('id')

->from('Robots');

// "SELECT id, name FROM Robots";

$builder->columns(['id', 'name'])

->from('Robots');

// "SELECT Robots.* FROM Robots WHERE Robots.name = 'Voltron'";

$builder->from('Robots')

->where('Robots.name = "Voltron"');

// "SELECT Robots.* FROM Robots WHERE Robots.id = 100";

$builder->from('Robots')

->where(100);

// "SELECT Robots.* FROM Robots WHERE Robots.type = 'virtual' AND Robots.id > 50";

$builder->from('Robots')

->where('type = "virtual"')

->andWhere('id > 50');

// "SELECT Robots.* FROM Robots WHERE Robots.type = 'virtual' OR Robots.id > 50";

$builder->from('Robots')

->where('type = "virtual"')

->orWhere('id > 50');

// "SELECT Robots.* FROM Robots GROUP BY Robots.name";

$builder->from('Robots')

->groupBy('Robots.name');

// "SELECT Robots.* FROM Robots GROUP BY Robots.name, Robots.id";

$builder->from('Robots')

->groupBy(['Robots.name', 'Robots.id']);

// "SELECT Robots.name SUM(Robots.price) FROM Robots GROUP BY Robots.name";

$builder->columns(['Robots.name', 'SUM(Robots.price)'])

->from('Robots')

->groupBy('Robots.name');

// "SELECT Robots.name, SUM(Robots.price) FROM Robots GROUP BY Robots.name HAVING SUM(Robots.price) > 1000";

$builder->columns(['Robots.name', 'SUM(Robots.price)'])

->from('Robots')

->groupBy('Robots.name')

->having('SUM(Robots.price) > 1000');

// "SELECT Robots.* FROM Robots JOIN RobotsParts";

$builder->from('Robots')

->join('RobotsParts');

// "SELECT Robots.* FROM Robots JOIN RobotsParts AS p";

$builder->from('Robots')

->join('RobotsParts', null, 'p');

// "SELECT Robots.* FROM Robots JOIN RobotsParts ON Robots.id = RobotsParts.robots_id AS p";

$builder->from('Robots')

->join('RobotsParts', 'Robots.id = RobotsParts.robots_id', 'p');

// "SELECT Robots.* FROM robots JOIN RobotsParts ON Robots.id = RobotsParts.robots_id AS p JOIN Parts ON Parts.id = RobotsParts.parts_id AS t";

$builder->from('Robots')

->join('RobotsParts', 'Robots.id = RobotsParts.robots_id', 'p')

->join('RobotsParts', 'Parts.id = RobotsParts.parts_id', 't');

// "SELECT r.* FROM Robots AS r";

$builder->addFrom('Robots', 'r');

// "SELECT Robots.*, p.* FROM Robots, Parts AS p";

$builder->from('Robots')

->addFrom('Parts', 'p');

// "SELECT r.*, p.* FROM Robots AS r, Parts AS p";

$builder->from(['r' => 'Robots'])

->addFrom('Parts', 'p');

// "SELECT r.*, p.* FROM Robots AS r, Parts AS p";

$builder->from(['r' => 'Robots', 'p' => 'Parts']);

// "SELECT Robots.* FROM Robots LIMIT 10";

$builder->from('Robots')

->limit(10);

// "SELECT Robots.* FROM Robots LIMIT 10 OFFSET 5";

$builder->from('Robots')

->limit(10, 5);

// "SELECT Robots.* FROM Robots WHERE id BETWEEN 1 AND 100";

$builder->from('Robots')

->betweenWhere('id', 1, 10);

// "SELECT Robots.* FROM Robots WHERE id IN (1, 2, 3)";

$builder->from('Robots')

->inWhere('id', [1, 2, 3]);

// "SELECT Robots.* FROM Robots WHERE id NOT IN (1, 2, 3)";

$builder->from('Robots')

->notInWhere('id', [1, 2, 3]);

// "SELECT Robots.* FROM Robots WHERE name LIKE '%Art%'";

$builder->from('Robots')

->where('name LIKE :name:', ['name' => '%' . $name . '%']);

// "SELECT r.* FROM Store\Robots WHERE r.name LIKE '%Art%'";

$builder->from(['r' => 'Store\Robots'])

->where('r.name LIKE :name:', ['name' => '%' . $name . '%']);

参数绑定(Bound Parameters)

查询构造器中的参数绑定可以在查询构建时设置，也可以在查询执行时设置：

// 构建查询时传递参数

$robots = $this->modelsManager->createBuilder()

->from('Robots')

->where('name = :name:', ['name' => $name])

->andWhere('type = :type:', ['type' => $type])

->getQuery()

->execute();

// 执行查询时传递参数

$robots = $this->modelsManager->createBuilder()

->from('Robots')

->where('name = :name:')

->andWhere('type = :type:')

->getQuery()

->execute(['name' => $name, 'type' => $type]);

禁用字面量(Disallow literals in PHQL)

PHQL中可以禁用字面量，这意味着如果禁用开启，则不能在PHQL语句中直接使用PHP字符串、数字和布尔值。如果在PHQL语句中嵌入外部数据，可能导致潜在的注入攻击：

$login = 'voltron';

$phql = "SELECT * FROM Models\Users WHERE login = '{$login}'";

$result = $manager->executeQuery($phql);

如果$login的值为' OR ' ' = ' ，将产生如下PHQL语句：

SELECT * FROM Models\Users WHERE login = '' OR '' = '';

无论存储在数据库中的login是何值，条件总是true。

如果字面量被禁用，在PHQL中使用PHP字面量会抛出异常，以强制开发者使用参数绑定。上面的查询这样写更安全：

$type = 'virtual';

$phql = "SELECT Robots.* FROM Robots WHERE Robots.type = :type:";

$result = $manager->executeQuery(

$phql,

[

'type' => $type,

]

);

可以通过以下方式禁用字面量：

use Phalcon\Mvc\Model;

Model::setup(

['phqlLiterals' => false]

);

无论字面量是否禁用，参数绑定都可以正常使用。禁用只是开发人员能够在web应用中采取的一项安全策略。

转义保留字(Escaping Reserved Words)

PHQL有一些保留字，如果想将保留字作为模型名或字段名使用，则需要使用转义分隔符[和]来转义关键字：

$phql = "SELECT * FROM [Update]";

$result = $manager->executeQuery($phql);

$phql = "SELECT id, [Like] FROM Posts";

$result = $manager->executeQuery($phql);

PHQL生命周期(PHQL Lifecycle)

作为高级语言，PHQL赋予了开发者个性化定制的能力，以满足不同的需求。以下是PHQL语句的生命周期：

PHQL被解析并转换为独立于数据库SQL之外的中间表示(IR)

根据模型对应的数据库系统，IR被转换为有效的SQL

PHQL语句被解析并保存在内存中，再次执行相同语句时速度会更快

使用原生SQL(Using Raw SQL)

某些数据库系统可能会提供PHQL不支持的特殊SQL扩展，这种情况适合使用原生SQL：

use Phalcon\Mvc\Model;

use Phalcon\Mvc\Model\Resultset\Simple as Resultset;

class Robots extends Model

{

public static function findByCreateInterval()

{

// 原生SQL

$sql = "SELECT * FROM robots WHERE id > 0";

// 模型

$robot = new Robots();

// 执行查询

return new Resultset(

null,

$robot,

$robot->getReadConnection()->query($sql)

);

}

}

如果原生SQL查询在应用中很普遍，可以在模型中添加通用方法：

use Phalcon\Mvc\Model;

use Phalcon\Mvc\Model\Resultset\Simple as Resultset;

class Robots extends Model

{

public static function findByRawSql($conditions, $params = null)

{

// 原生SQL

$sql = "SELECT * FROM robots WHERE {$conditions}";

// 模型

$robot = new Robots();

// 执行查询

return new Resultset(

null,

$robot,

$robot->getReadConnection()->query($sql),

);

}

}

上述findByRawSQL可以如下使用：

$robots = Robots::findByRawSql(

'id > ?',

[

10,

]

);

注意事项(Troubleshooting)

PHQL中的一些注意事项：

类名称区分大小写，如果定义类时名称和创建时的名称不一致，在大小写敏感的操作系统(如linux)中将导致不可预知行为

为保证参数绑定成功，连接数据库时必须指定正确的字符集

指定别名的类不能用完整命名空间替换，因为这项操作发生在PHP代码中，而非PHQL语句里

如果字段使用别名，应避免别名和字段名相同，不然查询解析器容易混淆。