php - mysql从两个表中查询两行

Question

我有这个查询来调用两个表中的信息。

DB::get("SELECT friends. * , (SELECT `login` FROM `users` WHERE `users`.`id` = friends.`user_id`) AS `login` FROM `friends` WHERE `id_user`='" . $this->user['id'] . "' ORDER BY `id` DESC LIMIT ")

因此，如果用户在好友列表中显示用户名，我想获得用户名和头像。头像行是 avatar 。 我试试这个。

DB::get("SELECT friends. * , (SELECT `login`, `*avatar*` FROM `users` WHERE `users`.`id` = friends.`user_id`) AS `login` FROM `friends` WHERE `id_user`='" . $this->user['id'] . "' ORDER BY `id` DESC LIMIT ")

然后告诉我错误

SQLSTATE[21000]: Cardinality violation: 1241 Operand should contain 1 column(s)

错在哪里？

Answer 1

首先你应该使用Prepared Statement其次，你不能写内联 View ，它有两列

SELECT friends. * , (SELECT `login`, `*avatar*` FROM ..

相反，您应该使用 JOIN，这可能比当前方法更有效并且更具可读性。