这个查询应该工作吗，如果不是，我如何使用PHP中的PDO将查询放入另一个查询中？
这是我的查询：
$userid = array($users->school_name_from_id($_SESSION['user_id']), $_SESSION['user_id'], $_SESSION['user_id']);
$statementString =
'SELECT * FROM schoolinfo
WHERE schoolinfo.school = ? AND
SELECT count(*) FROM friendstable
WHERE friendstable.user_ID = ?
AND frienstable.friend_ID = schoolinfo.id <= 0
AND
SELECT count(*) FROM friendstable
WHERE friendstable.user_ID = schoolinfo.id
AND friendstable.friend_ID = ? <= 0
ORDER BY RAND()
LIMIT 6';
$stmt = $database->_link->prepare($statementString);
$stmt->execute($userid);
$array = $stmt->fetchAll(PDO::FETCH_ASSOC);
print_r($array);
这是我在运行时得到的完整错误：
Fatal error: Uncaught exception 'PDOException' with message 'SQLSTATE[42000]: Syntax error or access violation: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'SELECT count(*) FROM friendstable WHERE friendstable.user_ID = '1' AND frienstab' at line 1' in C:'xampp'htdocs'thinkaztech'PHP'getSocialInformation.php:20 Stack trace: #0 C:'xampp'htdocs'thinkaztech'PHP'getSocialInformation.php(20): PDOStatement->execute(Array) #1 {main} thrown in C:'xampp'htdocs'thinkaztech'PHP'getSocialInformation.php on line 20
子查询必须放在括号内：
SELECT *
FROM schoolinfo
WHERE schoolinfo.school = ?
AND (
SELECT COUNT(*)
FROM friendstable
WHERE friendstable.user_ID = ?
AND friendstable.friend_ID = schoolinfo.id
) <= 0
AND (
SELECT COUNT(*)
FROM friendstable
WHERE friendstable.user_ID = schoolinfo.id
AND friendstable.friend_ID = ?
) <= 0
ORDER BY RAND()
LIMIT 6
请注意，在这种情况下，必须将双元素数组传递给 PDO::execute() 方法：
$stmt->execute([$userid, $userid]);
您可能还会发现，与使用这些相关的子查询相比，从数据库中获取所需结果的方法要有效得多。