Question

查询以获取所有具有理由的罪行以及罪犯和警察的名字，这就是我想要实现的目标。

这是我尝试过的：

SELECT crimes.user_police_id, crimes.user_criminal_id, crimes.reason, users.name
FROM `users`
INNER JOIN `crimes` on users.id = crimes.user_criminal_id

只返回罪犯的名字......

表格结构

CREATE TABLE users (
  id INT(11) AUTO_INCREMENT PRIMARY KEY,
  name VARCHAR(24)
);
INSERT INTO users (name) VALUES ("Divergent");
INSERT INTO users (name) VALUES ("SomeGuy");

CREATE TABLE crimes (
  id INT(11) AUTO_INCREMENT PRIMARY KEY,
  user_criminal_id INT(11),
  user_police_id INT(11),
  reason VARCHAR(256)
);
INSERT INTO crimes (user_criminal_id, user_police_id, reason) VALUES (2, 1, "Corruption");

这样可行，但只有警察名字

SELECT crimes.user_police_id, crimes.user_criminal_id, crimes.reason, c.name, p.name
FROM crimes
JOIN users c on c.id = crimes.user_criminal_id
JOIN users p on p.id = crimes.user_police_id

Answer 1

第二次加入users获取警察名称。

SELECT crimes.user_police_id, crimes.user_criminal_id, crimes.reason, u1.name AS criminal u2.name AS police
FROM `users` AS u1
INNER JOIN `crimes` on u1.id = crimes.user_criminal_id
INNER JOIN `users` AS u2 ON u2.id = crimes.user_police_id

Answer 2

你需要加倍加入。我更喜欢查询犯罪，所以你会明白为什么：

SELECT crimes.user_police_id, crimes.user_criminal_id, crimes.reason, c.name, p.name
FROM crimes
JOIN users c on users.id = crimes.user_criminal_id
JOIN users p on users.id = crimes.user_police_id

sql - 根据多个where子句从两个表中检索信息的查询

2 个答案: