我试图从大小为9 GB +的表中获取数据并拥有数百万条记录。我正在使用该数据填充DataTable。我从表中获取块的记录，即每页10个，通过Ajax和SQL Limit查询。
在上面的图像中，您可以看到我们有223,740页面，因此当我尝试访问最后一页时，查询将永远加载数据。但是，当我尝试访问第一页时，数据加载速度更快。但直接访问更高的偏移页面需要永远加载。
public static function getAllEvaluationsWithNameForDataTable($start){
$queryBuilder = new Builder();
return $queryBuilder
->from(array('e' => static::class))
->leftJoin('Cx\Framework\Models\Common\User\CxUser', 'e.cx_hc_user_id = u.id', 'u')
->columns('e.id, e.first_name, u.initials as assigned_coach, e.gender, e.email, e.phone, e.age, e.version, e.evaluation_status, e.ip_address, e.date_created, e.date_updated')
->orderBy('e.id asc')
->limit(10, $start)
->getQuery()
->execute()
->toArray();
}
PHP函数/控制器：
public function getEvaluationsAction() {
// Enable Json response
$this->setJsonResponse();
// This action can be called only via ajax
$this->requireAjax();
// Forward to access denied if current user is not allowed to view evaluation details
if (!$this->CxAuth->currentUserIsAllowedTo('VIEW', CxEbEvaluation::getClassResourceName()))
return $this->forwardToAccessDeniedError();
if(isset($_GET['start'])){
$start = $this->request->get('start');
}else{
$start = 10;
}
$recordsTotal = count(CxEbEvaluation::getAllForDataTable(array('id')));
//Get Evaluations from DB
$evaluation_quizzes = CxEbEvaluation::getAllEvaluationsWithNameForDataTable(intval($start));
//for getting base URL
$url = new Url();
$data = array();
foreach ($evaluation_quizzes as $key => $quiz) {
$data[ $key ][ 'id' ] = $quiz[ 'id' ];
$data[ $key ][ 'first_name' ] = $quiz[ 'first_name' ];
if($quiz[ 'assigned_coach' ]){
$data[ $key ][ 'assigned_coach' ] = $quiz['assigned_coach'];
}else{
$data[ $key ][ 'assigned_coach' ] = "Not assigned";
}
$data[ $key ][ 'gender' ] = $quiz[ 'gender' ];
$data[ $key ][ 'email' ] = $quiz[ 'email' ];
$data[ $key ][ 'phone' ] = $quiz[ 'phone' ];
$data[ $key ][ 'age' ] = $quiz[ 'age' ];
$data[ $key ][ 'version' ] = $quiz[ 'version' ];
$data[ $key ][ 'quiz' ] = $url->get('/admin/get-evaluation-quiz-by-id');
$data[ $key ][ 'manage-notes-messages-and-calls' ] = $url->get('/admin/manage-notes-messages-and-calls');
$data[ $key ][ 'date_created' ] = date("m/d/Y H:i:s", $quiz[ 'date_created' ]);
$data[ $key ][ 'evaluation_status' ] = $quiz[ 'evaluation_status' ];
}
// Return data array
return array(
"recordsTotal" => $recordsTotal,
"recordsFiltered" => $recordsTotal ,
"data" => $data //How To Retrieve This Data
);
// Return data
}
使用Javascript：
cx.common.data.cxAdminDataTables.EbEvaluation = $CxRecordsTable.cxAdminDataTable({
ajaxUrl: '<?php echo $this->CxHelper->Route('eb-admin-get-evaluations')?>' + eqQuizIdQueryString,
serverSide: true,
processing: true,
recordsFiltered :true,
columns: [
cx.common.admin.tableEditColumn('id',{ delete: true }),
{ data: 'first_name' },
{ data: 'assigned_coach' },
{ data: 'gender' },
{ data: 'email' },
{ data: 'phone' },
{ data: 'age' },
cx.common.admin.tableLinkColumn('quiz', quizLinkOptions),
cx.common.admin.tableEditColumn('id', healthCoachLinkOptions),
cx.common.admin.tableLinkColumn('manage-notes-messages-and-calls', manageNotesMessagesAndCalls),
{ data: 'date_created' },
cx.common.admin.tableSwitchableColumn('evaluation_status', {
editable: true,
createdCell: function (td, cellData, rowData, row, col){
$(td).data('evaluation-status-id', rowData.id);
},
onText: 'Complete',
offText: 'In progress'
})
],
toolbarOptions:{
enabled: false
}, success: function (data) {
cx.common.data.cxAdminDataTables.EbEvaluation.cxAdminDataTable("reloadAjax");
}
});
}
else {
$row.removeClass('alert');
}
});
}
});
我希望这个问题很清楚。如果需要其他任何东西，请更新我，我将提供。
（来自评论）
SELECT e.id` AS id, e.first_name AS first_name,
u.initials AS assigned_coach,
e.gender AS gender, e.email AS email, e.phone AS phone,
e.age AS age, e.version AS version,
e.evaluation_status AS evaluation_status,
e.ip_address AS ip_address, e.date_created AS date_created,
e.date_updated AS date_updated
FROM evaluation_client AS e
LEFT JOIN cx_user AS u ON e.cx_hc_user_id = u.id
ORDER BY e.id ASC
LIMIT :APL0 OFFSET, :APL1
由Masivuye Cokile链接的Why does MYSQL higher LIMIT offset slow the query down?问题和答案，以及那里提供的https://explainextended.com/2009/10/23/mysql-order-by-limit-performance-late-row-lookups/链接，包含了关于为什么大偏移查询缓慢的优秀纲要。基本上，对于LIMIT 150000, 10，MySQL仍会扫描整个150000行，即使它稍后丢弃它们。为了加快速度，您可以：
count查询计算的近似页码。id上创建索引，然后强制mysql执行仅索引搜索。对于第二种方法，您必须重写查询
SELECT ...
FROM table t
WHERE ...
ORDER by t.id ASC
LIMIT 150000, 10
至
SELECT ...
FROM (
SELECT id
FROM table
ORDER BY
id ASC
LIMIT 150000, 10
) o
JOIN table t
ON t.id = o.id
WHERE ...
ORDER BY t.id ASC
或者，由于您不局限于单个查询，因此您可以使用查找页面上第一个项目的ID
SELECT id
FROM table
ORDER BY id ASC
LIMIT 150000, 1
然后使用所述id来检索实际数据：
SELECT ...
FROM table
WHERE id >= $id
AND ...
ORDER BY id ASC
LIMIT 0, 10
模式SELECT whatever FROM vast_table ORDER BY something LIMIT 10 large_number是一个臭名昭着的性能反模式。为什么？因为它必须检查很多行才能返回一些。
如果您的id值是主键（或任何索引列），则可以对其进行分页
SELECT whatever FROM vast_table WHERE id BETWEEN large_value AND large_value+9 ORDER BY id;
或者你可以试试
SELECT whatever FROM vast_table WHERE id >= large_value ORDER BY id LIMIT 10;
如果您的id值存在空白，则不会完美地分页。但它的表现相当不错。
该问题与我的表中的日期列数据类型有关。我在日期字段中使用int数据类型，当我将日期列的数据类型更改为datetime时，搜索结果以秒为单位。
我找到解决方案@ http://dbscience.blogspot.com/2008/08/can-timestamp-be-slower-than-datetime.html的来源