Php 如何加入我的mysql表

通常我这样做是为了得到两张桌子

<?php 
$select = "SELECT * FROM question ORDER BY id DESC LIMIT 0,20";
$query  = $db->query($select);

while ($fetch = $db->fetch($query)) {
    $uselect = "SELECT * FROM user WHERE id='".intval($fetch['q_user'])."' ";
    $uquery  = $db->query($uselect);
    $ufetch = $db->fetch($uquery);
    ?>    

    Title : <?php echo $fetch['q_title']; ?>
    User : <?php echo $ufetch['u_id']; ?>

    <?php 
} 
?>

好吧，你可以：

SELECT *
FROM question
JOIN user ON question.q_user = user.id
ORDER BY question.id DESC
LIMIT 0, 20

我建议明确列出列，因为任何重叠（Question.id和user.id）都是不明确的。只需执行
选择question.id，user.id作为uid，…

SELECT * FROM question JOIN user ON question.q_user = user.id ORDER BY question.id DESC LIMIT 0, 20

有用链接：
此查询应该是正确的：

create table questions
 (
    question_id bigint unsigned auto_increment primary key,
    user_id bigint unsigned not null,
    title varchar(255),
 )engine=innodb;

 create table users
 (
    user_id bigint unsigned auto_increment primary key,
    name varchar(255) not null
 )engine=innodb;

 // your query
 select q.* from questions q
 inner join users u where u.user_id = q.user_id
 order by q.question_id desc

是的，我假设您希望返回询问问题的用户，因为您存储q_用户，然后需要执行一些SQL操作，如：

从问题q中选择q.q\u标题、u.u\u id加入用户u ON（q.q\u用户=u.u\u id）

您可以将您的限制等应用于此查询

SELECT * FROM question JOIN user ON question.q_user = user.id ORDER BY question.id DESC LIMIT 0, 20

create table questions
 (
    question_id bigint unsigned auto_increment primary key,
    user_id bigint unsigned not null,
    title varchar(255),
 )engine=innodb;

 create table users
 (
    user_id bigint unsigned auto_increment primary key,
    name varchar(255) not null
 )engine=innodb;

 // your query
 select q.* from questions q
 inner join users u where u.user_id = q.user_id
 order by q.question_id desc