如何改进此SQL查询（SQLite和PHP）

我正在基于SQLite中多个db表的数据呈现一个数组

表：

staff-包含可以拥有证书的所有用户/工作人员 证书包含用户可以拥有的所有可用证书 rel\u staff\u certificate—包含与用户相关的证书 桌上工作人员

表格证书

表rel\uuuu员工证书

这就是交易：

// Get all available certificates
$sql_get_cert = "SELECT * FROM certificates ORDER BY cert_id ASC";

// Get all certificates for staff user
$sql_get_staff_cert_rel = "SELECT * FROM rel__staff_certificate WHERE staff_id = :staff_id AND cert_id = :cert_id LIMIT 1";

// Prepare SQL queries...
$get_cert_rel = $PDODB->prepare($sql_get_staff_cert_rel);
$get_cert = $PDODB->prepare($sql_get_cert);

// Get all certificates to array $certdata
$get_cert->execute();
$certdata = $get_cert->fetchAll();

// Create the array where I want to push data to:
$staffdata[$i] = array(
    $staff['staff_id'], // $staff() is populated earlier and works just fine
    $staff['name'],
    $ccdata['region'],  // $ccdata() is populated earlier and works just fine
    $ccdata['cc_code']
);

// Loop through all available certificates in table ´certificates´
foreach ($certdata as $cert) {
    // Bind values for the relation SQL now when we have them all
    $get_cert_rel->bindValue(':staff_id', $staff['staff_id']);
    $get_cert_rel->bindValue(':cert_id', $cert['cert_id']);
    $get_cert_rel->execute();

    // Get the certification relation data to array $certreldata()
    $certreldata = $get_cert_rel->fetch();

    // If a certificate date exists, then use that for our array which tells us that this staff has this certificate and was certified on this date
    if (!empty($certreldata['cert_date'])) { 
        array_push($staffdata[$i], $certreldata['cert_date']);
    }
    // If no certificate date exsits, then just add value "N/A" as not available
    else {
        array_push($staffdata[$i], 'N/A');
    }
}

好了，就这样！这是可行的，但正如您所看到的，我在foreach循环中对SQL server执行了大量SQL操作，我认为这不是很好，因为这将消耗大量不必要的时间

谁能告诉我如何用一个SQL查询来代替？或者告诉我如何改进代码以在其他方面进一步加快速度

---

谢谢。

这可以通过加入来完成：

选择证书日期 从证书 使用证书id加入相关员工证书 其中staff_id=？

---

尝试使用SQL连接。下面是一个提供相关信息的示例：

选择 staff.staff\u id， staff.name， 证书.说明， 证书.说明， 相关人员证书。证书日期， rel_uuustaff_certificate.comments 来自rel____证书员工 certificates.cert\u id=rel\u staff\u certificate.cert\u id上的内部连接证书 staff.staff\u id=rel\u staff\u certificate.staff\u id上的内部加入staff 其中staff.staff_id=？ 如果您希望所有员工在一次查询中拥有所有证书，则WHERE语句可能是可选的。

您可以使用JOIN进行此类查询

使用左联接可以使用第一个表LEFT的私钥和第二个表right的外键联接两个表，而如果在第二个表right中找不到行，则右表的列将填充空值：

选择c* 从证书中选择c 在sc.cert\u id=c.cert\u id上以sc身份左加入相关人员证书 其中sc.staff_id=？ 按c.cert\u id订购 使用内部联接可以使用与“左联接”相同的方式联接两个表，但如果右表中没有左表的私钥条目，则跳过这些行：

选择c* 从证书中选择c 在sc.cert\u id=c.cert\u id上作为sc的内部加入相关人员证书 其中sc.staff_id=？ 按c.cert\u id订购

---

有关联接的更多信息，请参阅文档-基本结构和。

使用联接如何？谢谢您的帮助！谢谢你的回答！谢谢你的回答！

`cert_id`   INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
`caption`   TEXT NOT NULL,
`description`   TEXT

`rel_id`    INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
`staff_id`  INTEGER,
`cert_id`   INTEGER,
`cert_date` TEXT NOT NULL,
`comments`  TEXT

// Get all available certificates
$sql_get_cert = "SELECT * FROM certificates ORDER BY cert_id ASC";

// Get all certificates for staff user
$sql_get_staff_cert_rel = "SELECT * FROM rel__staff_certificate WHERE staff_id = :staff_id AND cert_id = :cert_id LIMIT 1";

// Prepare SQL queries...
$get_cert_rel = $PDODB->prepare($sql_get_staff_cert_rel);
$get_cert = $PDODB->prepare($sql_get_cert);

// Get all certificates to array $certdata
$get_cert->execute();
$certdata = $get_cert->fetchAll();

// Create the array where I want to push data to:
$staffdata[$i] = array(
    $staff['staff_id'], // $staff() is populated earlier and works just fine
    $staff['name'],
    $ccdata['region'],  // $ccdata() is populated earlier and works just fine
    $ccdata['cc_code']
);

// Loop through all available certificates in table ´certificates´
foreach ($certdata as $cert) {
    // Bind values for the relation SQL now when we have them all
    $get_cert_rel->bindValue(':staff_id', $staff['staff_id']);
    $get_cert_rel->bindValue(':cert_id', $cert['cert_id']);
    $get_cert_rel->execute();

    // Get the certification relation data to array $certreldata()
    $certreldata = $get_cert_rel->fetch();

    // If a certificate date exists, then use that for our array which tells us that this staff has this certificate and was certified on this date
    if (!empty($certreldata['cert_date'])) { 
        array_push($staffdata[$i], $certreldata['cert_date']);
    }
    // If no certificate date exsits, then just add value "N/A" as not available
    else {
        array_push($staffdata[$i], 'N/A');
    }
}