Php 对同一子查询表达式的多个联接

我最近一直在自学SQL，并一直在做一个玩具项目来做到这一点。下面是一个示例模式：

CREATE TABLE user (
  id INT PRIMARY KEY NOT NULL AUTO_INCREMENT,
  name VARCHAR(50)
);

INSERT INTO user(name) VALUES
  ("User 1"),
  ("User 2"),
  ("User 3"),
  ("User 4"),
  ("User 5");

CREATE TABLE friendship (
  uid_1 INT,
  uid_2 INT,
  accepted_time TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
  PRIMARY KEY (uid_1, uid_2),
  CONSTRAINT fk_uid_1 FOREIGN KEY (uid_1) REFERENCES user (id),
  CONSTRAINT fk_uid_2 FOREIGN KEY (uid_2) REFERENCES user (id)
);

INSERT INTO friendship(uid_1, uid_2) VALUES
  (1, 2),
  (2, 1);

CREATE TABLE event (
  id INT PRIMARY KEY NOT NULL AUTO_INCREMENT,
  name VARCHAR(50),
  owner_id INT,
  CONSTRAINT fk_owner_id FOREIGN KEY (owner_id) REFERENCES user (id)
);

INSERT INTO event (name, owner_id) VALUES
 ("Event 1", 1),
 ("Event 2", 2),
 ("Event 3", 3),
 ("Event 4", 4),
 ("Event 5", 5),
 ("Event 6", 1);

CREATE TABLE invite (
  event_id INT NOT NULL,
  sent_from_id INT NOT NULL,
  sent_to_id INT NOT NULL,
  PRIMARY KEY (event_id, sent_to_id),
  CONSTRAINT fk_event_id FOREIGN KEY (event_id) REFERENCES event (id),
  CONSTRAINT fk_sent_from_id FOREIGN KEY (sent_from_id) REFERENCES user (id),
  CONSTRAINT fk_sent_to_id FOREIGN KEY (sent_to_id) REFERENCES user (id)
);

INSERT INTO invite(event_id, sent_from_id, sent_to_id) VALUES
  (1, 2, 3);

作为这个项目的一部分，我有一个查询，它获取一个用户列表，其中包含与当前经过身份验证的用户相关的信息

查询的简化版本如下所示：

$select_users_query = "

SELECT
    user.id AS id,
    user.name AS name,
    friendship.accepted_time AS friend_since
FROM user
LEFT JOIN friendship
    ON friendship.uid_1 = user.id AND friendship.uid_2 = $relative_to_id

";

然后，在某些端点，我想返回具有一个或多个用户作为子对象的对象。为了做到这一点，我一直将表作为子查询连接到上述查询中，但是当返回的对象有多个用户（例如，事件邀请有一个发送用户、一个接收用户和一个拥有相关事件的用户）时，生成的查询可能会非常重复：

$select_invites_query = "

SELECT
    event.id AS event_id,
    event.name AS event_name,

    owner.id AS owner_id,
    owner.name AS owner_name,
    owner.friend_since AS owner_friend_since,

    sent_to.id AS sent_to_id,
    sent_to.name AS sent_to_name,
    sent_to.friend_since AS sent_to_friend_since,

    sent_from.id AS sent_from_id,
    sent_from.name AS sent_from_name,
    sent_from.friend_since AS sent_from_friend_since,

FROM invite

INNER JOIN event
    ON event.id = invite.event_id

INNER JOIN ($select_users_query) owner
    ON event.owner_id = owner.id

INNER JOIN ($select_users_query) sent_from
    ON invite.sent_from_id = sent_from.id

INNER JOIN ($select_users_query) sent_to
    ON invite.sent_to_id = sent_to.id

";

我的问题是：

假设

内部联接只在一行上匹配，那么在执行过程中重复这样的子查询是性能问题吗

如果不是，那么

$select\u查询

所需的额外解析是否是一个值得关注的问题（尤其是当

$select\u用户\u查询

变得庞大和复杂时）

在这里使用变量是好主意还是坏主意？从我对

EXPLAIN

的检查来看，MySQL似乎能够非常有效地处理这些

JOIN

s，但是定义变量会迫使MySQL在

JOIN

ing之前将未过滤的结果集拉入内存吗

---

参见SQL FaldSchema。

，因为您似乎需要同一个查询的自联接，请考虑一个（在MySQL 8 +中可用）和PHP参数化。下面以面向对象和过程的方式演示如何使用PHP的API：

$select_invites_query = "
 WITH sub AS (
    SELECT u.id AS id, u.`name` AS `name`, 
           f.accepted_time AS friend_since 
    FROM user 
    LEFT JOIN friendship f
          ON f.uid_1 = u.id AND f.uid_2 = ?
 )

 SELECT event.id AS event_id, event.`name` AS event_name, 
        owner.id AS owner_id, owner.`name` AS owner_name, 
        owner.friend_since AS owner_friend_since,

        sent_to.id AS sent_to_id, sent_to.`name` AS sent_to_name, 
        sent_to.friend_since AS sent_to_friend_since, 

        sent_from.id AS sent_from_id, sent_from.`name` AS sent_from_name, 
        sent_from.friend_since AS sent_from_friend_since

 FROM invite 
 INNER JOIN event 
    ON event.id = invite.event_id 
 INNER JOIN sub owner 
    ON event.owner_id = owner.id 
 INNER JOIN sub sent_from 
    ON invite.sent_from_id = sent_from.id 
 INNER JOIN sub sent_to 
    ON invite.sent_to_id = sent_to.id";

// OBJECT-ORIENTED STYLE
$conn = new mysqli("my_host", "my_user", "my_pwd", "my_db");
$stmt = $conn->prepare($select_invites_query))
$stmt->bind_param("i", $relative_to_id);
$stmt->execute();
...

// PROCEDURAL STYLE     
$conn = mysqli_connect("my_host", "my_user", "my_pwd", "my_db");
$stmt = mysqli_prepare($conn, $select_invites_query);
mysqli_stmt_bind_param($stmt, "i", $relative_to_id); 
mysqli_stmt_execute($stmt); 
...

---

因为您需要自己加入相同的查询，请考虑一个（在MySQL 8 +中可用）和PHP参数化。下面以面向对象和过程的方式演示如何使用PHP的API：

$select_invites_query = "
 WITH sub AS (
    SELECT u.id AS id, u.`name` AS `name`, 
           f.accepted_time AS friend_since 
    FROM user 
    LEFT JOIN friendship f
          ON f.uid_1 = u.id AND f.uid_2 = ?
 )

 SELECT event.id AS event_id, event.`name` AS event_name, 
        owner.id AS owner_id, owner.`name` AS owner_name, 
        owner.friend_since AS owner_friend_since,

        sent_to.id AS sent_to_id, sent_to.`name` AS sent_to_name, 
        sent_to.friend_since AS sent_to_friend_since, 

        sent_from.id AS sent_from_id, sent_from.`name` AS sent_from_name, 
        sent_from.friend_since AS sent_from_friend_since

 FROM invite 
 INNER JOIN event 
    ON event.id = invite.event_id 
 INNER JOIN sub owner 
    ON event.owner_id = owner.id 
 INNER JOIN sub sent_from 
    ON invite.sent_from_id = sent_from.id 
 INNER JOIN sub sent_to 
    ON invite.sent_to_id = sent_to.id";

// OBJECT-ORIENTED STYLE
$conn = new mysqli("my_host", "my_user", "my_pwd", "my_db");
$stmt = $conn->prepare($select_invites_query))
$stmt->bind_param("i", $relative_to_id);
$stmt->execute();
...

// PROCEDURAL STYLE     
$conn = mysqli_connect("my_host", "my_user", "my_pwd", "my_db");
$stmt = mysqli_prepare($conn, $select_invites_query);
mysqli_stmt_bind_param($stmt, "i", $relative_to_id); 
mysqli_stmt_execute($stmt); 
...

---

谢谢，稍后将提供。与其重复使用查询作为子查询，不如为用户和友谊表创建一个连接。3次重复相同的查询意味着通过加入这2个表来做相同的事情3次肯定会有性能改进。@NandanRana您能澄清一下您的确切意思吗？您将如何更改加入策略？@草莓添加了一个指向SQL Fiddle设置的链接。您的MySQL版本是什么？使用8+，您可以利用CTEs。谢谢，稍后将提供。与其重复使用查询作为子查询，不如为用户和友谊表创建连接。3次重复相同的查询意味着通过加入这2个表来做相同的事情3次肯定会有性能改进。@NandanRana您能澄清一下您的确切意思吗？您将如何更改加入策略？@草莓添加了一个指向SQL Fiddle设置的链接。您的MySQL版本是什么？使用8+，您可以利用CTE。