如何查询JOIN表的第二列？

Question

我想查询4号人物的朋友的姓名，所以'otherPerson_id'中的数字，但我的尝试只查询'person_id'中的id或名字。我怎么能要求查询关于4号人的朋友的信息，而不是关于4号人本身的信息呢？

这是我的尝试：

$q = "SELECT DISTINCT p.idperson, p.name FROM person p INNER JOIN people_friends pf ON p.idperson = pf.person_id AND p.idperson = 4";
        $res = $connexion->query($q);
        $res->setFetchMode(PDO::FETCH_COLUMN);
        while($record = $res->fetch()) {
            echo $record[name];
            echo "<br/>";
        }

表:(所以当我寻找4号人的朋友时，我希望它返回1和7）

编辑：

CREATE TABLE people_friends
(
  person_id integer NOT NULL,
  otherperson_id integer NOT NULL,
  CONSTRAINT people_friends_pkey PRIMARY KEY (person_id, otherperson_id),
  CONSTRAINT people_friends_person_id_fkey FOREIGN KEY (person_id)
      REFERENCES person (idperson) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
  CONSTRAINT people_friends_person_id_fkey1 FOREIGN KEY (person_id)
      REFERENCES person (idperson) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION
)



CREATE TABLE person
(
  idperson integer NOT NULL,
  name character varying(50),
  map bytea,
  CONSTRAINT person_pkey PRIMARY KEY (idperson)
)

由于

Answer 1

尝试此查询。

SELECT DISTINCT

pFriend.idperson, pFriend.name

FROM people_friends pf 

INNER JOIN person pFriend on pf.otherperson_id = pFriend.idperson

WHERE

pf.person_id = 4

Answer 2

您只需添加一个WHERE子句来检查pf表。

SELECT DISTINCT p.idperson
               ,p.name 
FROM person p 
  INNER JOIN people_friends pf 
    ON p.idperson = pf.person_id 
WHERE pf.otherperson_id = 4