Notice (8): file_put_contents(): Write of 270 bytes failed with errno=28 No space left on device [CORE/src/Log/Engine/FileLog.php, line 140]

        if (!$mask) {
            file_put_contents($pathname, $message . "\n", FILE_APPEND);

file_put_contents - [internal], line ??
Cake\Log\Engine\FileLog::log() - CORE/src/Log/Engine/FileLog.php, line 140
Cake\Log\Log::write() - CORE/src/Log/Log.php, line 392
Cake\Log\Log::warning() - CORE/src/Log/Log.php, line 477
DebugKit\ToolbarService::isSuspiciouslyProduction() - ROOT/vendor/cakephp/debug_kit/src/ToolbarService.php, line 169
DebugKit\ToolbarService::isEnabled() - ROOT/vendor/cakephp/debug_kit/src/ToolbarService.php, line 105
DebugKit\Plugin::bootstrap() - ROOT/vendor/cakephp/debug_kit/src/Plugin.php, line 48
Cake\Http\BaseApplication::pluginBootstrap() - CORE/src/Http/BaseApplication.php, line 182
Cake\Http\Server::bootstrap() - CORE/src/Http/Server.php, line 111
Cake\Http\Server::run() - CORE/src/Http/Server.php, line 79
[main] - ROOT/webroot/index.php, line 40

Notice (8): unserialize() [<a href='https://secure.php.net/function.unserialize'>function.unserialize</a>]: Error at offset 16363 of 16373 bytes [APP/Controller/NewsController.php, line 5571]

Code Context

               {
                      $a=unserialize($line2);
               }

unserialize - [internal], line ??
App\Controller\NewsController::action_cache() - APP/Controller/NewsController.php, line 5571
App\Controller\NewsController::cache_action() - APP/Controller/NewsController.php, line 5281
App\Controller\NewsController::action_() - APP/Controller/NewsController.php, line 6481
App\Controller\NewsController::get_data() - APP/Controller/NewsController.php, line 5701
App\Controller\NewsController::action_cache() - APP/Controller/NewsController.php, line 5625
App\Controller\NewsController::cache_action() - APP/Controller/NewsController.php, line 5281
App\Controller\NewsController::view() - APP/Controller/NewsController.php, line 3436
Cake\Controller\Controller::invokeAction() - CORE/src/Controller/Controller.php, line 539
Cake\Controller\ControllerFactory::handle() - CORE/src/Controller/ControllerFactory.php, line 140
Cake\Controller\ControllerFactory::invoke() - CORE/src/Controller/ControllerFactory.php, line 115
Cake\Http\BaseApplication::handle() - CORE/src/Http/BaseApplication.php, line 317
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 77
Cake\Http\Middleware\CsrfProtectionMiddleware::process() - CORE/src/Http/Middleware/CsrfProtectionMiddleware.php, line 174
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\I18n\Middleware\LocaleSelectorMiddleware::process() - CORE/src/I18n/Middleware/LocaleSelectorMiddleware.php, line 61
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73

Warning (2): Undefined array key "nsort" [APP/Controller/NewsController.php, line 3613]

Code Context

                
                $nav_url.="<a href='".$website_info[0]["nsort"]["nsort_url"]."'>".$website_info[0]["nsort"]["nsort_name"]."</a>";

App\Controller\NewsController::view() - APP/Controller/NewsController.php, line 3613
Cake\Controller\Controller::invokeAction() - CORE/src/Controller/Controller.php, line 539
Cake\Controller\ControllerFactory::handle() - CORE/src/Controller/ControllerFactory.php, line 140
Cake\Controller\ControllerFactory::invoke() - CORE/src/Controller/ControllerFactory.php, line 115
Cake\Http\BaseApplication::handle() - CORE/src/Http/BaseApplication.php, line 317
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 77
Cake\Http\Middleware\CsrfProtectionMiddleware::process() - CORE/src/Http/Middleware/CsrfProtectionMiddleware.php, line 174
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\I18n\Middleware\LocaleSelectorMiddleware::process() - CORE/src/I18n/Middleware/LocaleSelectorMiddleware.php, line 61
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Http\Middleware\BodyParserMiddleware::process() - CORE/src/Http/Middleware/BodyParserMiddleware.php, line 157
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Routing\Middleware\RoutingMiddleware::process() - CORE/src/Routing/Middleware/RoutingMiddleware.php, line 161
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Routing\Middleware\AssetMiddleware::process() - CORE/src/Routing/Middleware/AssetMiddleware.php, line 77
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Error\Middleware\ErrorHandlerMiddleware::process() - CORE/src/Error/Middleware/ErrorHandlerMiddleware.php, line 126

Warning (2): Trying to access array offset on value of type null [APP/Controller/NewsController.php, line 3613]

Code Context

                
                $nav_url.="<a href='".$website_info[0]["nsort"]["nsort_url"]."'>".$website_info[0]["nsort"]["nsort_name"]."</a>";

App\Controller\NewsController::view() - APP/Controller/NewsController.php, line 3613
Cake\Controller\Controller::invokeAction() - CORE/src/Controller/Controller.php, line 539
Cake\Controller\ControllerFactory::handle() - CORE/src/Controller/ControllerFactory.php, line 140
Cake\Controller\ControllerFactory::invoke() - CORE/src/Controller/ControllerFactory.php, line 115
Cake\Http\BaseApplication::handle() - CORE/src/Http/BaseApplication.php, line 317
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 77
Cake\Http\Middleware\CsrfProtectionMiddleware::process() - CORE/src/Http/Middleware/CsrfProtectionMiddleware.php, line 174
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\I18n\Middleware\LocaleSelectorMiddleware::process() - CORE/src/I18n/Middleware/LocaleSelectorMiddleware.php, line 61
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Http\Middleware\BodyParserMiddleware::process() - CORE/src/Http/Middleware/BodyParserMiddleware.php, line 157
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Routing\Middleware\RoutingMiddleware::process() - CORE/src/Routing/Middleware/RoutingMiddleware.php, line 161
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Routing\Middleware\AssetMiddleware::process() - CORE/src/Routing/Middleware/AssetMiddleware.php, line 77
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Error\Middleware\ErrorHandlerMiddleware::process() - CORE/src/Error/Middleware/ErrorHandlerMiddleware.php, line 126

Warning (2): Undefined array key "nsort" [APP/Controller/NewsController.php, line 3613]

Code Context

                
                $nav_url.="<a href='".$website_info[0]["nsort"]["nsort_url"]."'>".$website_info[0]["nsort"]["nsort_name"]."</a>";

App\Controller\NewsController::view() - APP/Controller/NewsController.php, line 3613
Cake\Controller\Controller::invokeAction() - CORE/src/Controller/Controller.php, line 539
Cake\Controller\ControllerFactory::handle() - CORE/src/Controller/ControllerFactory.php, line 140
Cake\Controller\ControllerFactory::invoke() - CORE/src/Controller/ControllerFactory.php, line 115
Cake\Http\BaseApplication::handle() - CORE/src/Http/BaseApplication.php, line 317
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 77
Cake\Http\Middleware\CsrfProtectionMiddleware::process() - CORE/src/Http/Middleware/CsrfProtectionMiddleware.php, line 174
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\I18n\Middleware\LocaleSelectorMiddleware::process() - CORE/src/I18n/Middleware/LocaleSelectorMiddleware.php, line 61
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Http\Middleware\BodyParserMiddleware::process() - CORE/src/Http/Middleware/BodyParserMiddleware.php, line 157
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Routing\Middleware\RoutingMiddleware::process() - CORE/src/Routing/Middleware/RoutingMiddleware.php, line 161
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Routing\Middleware\AssetMiddleware::process() - CORE/src/Routing/Middleware/AssetMiddleware.php, line 77
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Error\Middleware\ErrorHandlerMiddleware::process() - CORE/src/Error/Middleware/ErrorHandlerMiddleware.php, line 126

Warning (2): Trying to access array offset on value of type null [APP/Controller/NewsController.php, line 3613]

Code Context

                
                $nav_url.="<a href='".$website_info[0]["nsort"]["nsort_url"]."'>".$website_info[0]["nsort"]["nsort_name"]."</a>";

App\Controller\NewsController::view() - APP/Controller/NewsController.php, line 3613
Cake\Controller\Controller::invokeAction() - CORE/src/Controller/Controller.php, line 539
Cake\Controller\ControllerFactory::handle() - CORE/src/Controller/ControllerFactory.php, line 140
Cake\Controller\ControllerFactory::invoke() - CORE/src/Controller/ControllerFactory.php, line 115
Cake\Http\BaseApplication::handle() - CORE/src/Http/BaseApplication.php, line 317
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 77
Cake\Http\Middleware\CsrfProtectionMiddleware::process() - CORE/src/Http/Middleware/CsrfProtectionMiddleware.php, line 174
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\I18n\Middleware\LocaleSelectorMiddleware::process() - CORE/src/I18n/Middleware/LocaleSelectorMiddleware.php, line 61
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Http\Middleware\BodyParserMiddleware::process() - CORE/src/Http/Middleware/BodyParserMiddleware.php, line 157
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Routing\Middleware\RoutingMiddleware::process() - CORE/src/Routing/Middleware/RoutingMiddleware.php, line 161
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Routing\Middleware\AssetMiddleware::process() - CORE/src/Routing/Middleware/AssetMiddleware.php, line 77
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Error\Middleware\ErrorHandlerMiddleware::process() - CORE/src/Error/Middleware/ErrorHandlerMiddleware.php, line 126

Notice (8): unserialize() [<a href='https://secure.php.net/function.unserialize'>function.unserialize</a>]: Error at offset 4067 of 4085 bytes [APP/Controller/NewsController.php, line 5571]

Code Context

               {
                      $a=unserialize($line2);
               }

unserialize - [internal], line ??
App\Controller\NewsController::action_cache() - APP/Controller/NewsController.php, line 5571
App\Controller\NewsController::cache_action() - APP/Controller/NewsController.php, line 5281
App\Controller\NewsController::article_show() - APP/Controller/NewsController.php, line 4290
App\Controller\NewsController::view() - APP/Controller/NewsController.php, line 3822
Cake\Controller\Controller::invokeAction() - CORE/src/Controller/Controller.php, line 539
Cake\Controller\ControllerFactory::handle() - CORE/src/Controller/ControllerFactory.php, line 140
Cake\Controller\ControllerFactory::invoke() - CORE/src/Controller/ControllerFactory.php, line 115
Cake\Http\BaseApplication::handle() - CORE/src/Http/BaseApplication.php, line 317
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 77
Cake\Http\Middleware\CsrfProtectionMiddleware::process() - CORE/src/Http/Middleware/CsrfProtectionMiddleware.php, line 174
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\I18n\Middleware\LocaleSelectorMiddleware::process() - CORE/src/I18n/Middleware/LocaleSelectorMiddleware.php, line 61
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Http\Middleware\BodyParserMiddleware::process() - CORE/src/Http/Middleware/BodyParserMiddleware.php, line 157
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Routing\Middleware\RoutingMiddleware::process() - CORE/src/Routing/Middleware/RoutingMiddleware.php, line 161

Notice (8): unserialize() [<a href='https://secure.php.net/function.unserialize'>function.unserialize</a>]: Error at offset 61409 of 61429 bytes [APP/Controller/NewsController.php, line 5571]

Code Context

               {
                      $a=unserialize($line2);
               }

unserialize - [internal], line ??
App\Controller\NewsController::action_cache() - APP/Controller/NewsController.php, line 5571
App\Controller\NewsController::cache_action() - APP/Controller/NewsController.php, line 5281
App\Controller\NewsController::article_show() - APP/Controller/NewsController.php, line 4310
App\Controller\NewsController::view() - APP/Controller/NewsController.php, line 3822
Cake\Controller\Controller::invokeAction() - CORE/src/Controller/Controller.php, line 539
Cake\Controller\ControllerFactory::handle() - CORE/src/Controller/ControllerFactory.php, line 140
Cake\Controller\ControllerFactory::invoke() - CORE/src/Controller/ControllerFactory.php, line 115
Cake\Http\BaseApplication::handle() - CORE/src/Http/BaseApplication.php, line 317
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 77
Cake\Http\Middleware\CsrfProtectionMiddleware::process() - CORE/src/Http/Middleware/CsrfProtectionMiddleware.php, line 174
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\I18n\Middleware\LocaleSelectorMiddleware::process() - CORE/src/I18n/Middleware/LocaleSelectorMiddleware.php, line 61
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Http\Middleware\BodyParserMiddleware::process() - CORE/src/Http/Middleware/BodyParserMiddleware.php, line 157
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Routing\Middleware\RoutingMiddleware::process() - CORE/src/Routing/Middleware/RoutingMiddleware.php, line 161

深入浅析SQL中的groupby和having用法

Warning (2): Undefined array key "nsort" [ROOT/plugins/Kuhuang/templates/Websites/view.php, line 430]

Code Context

          <div class="info"> 
            <span><a href="<?php echo $website_info[0]["nsort"]["nsort_url"];?>"><i class="fa fa-columns"></i><?php echo $website_info[0]["nsort"]["nsort_name"];?></a></span> 
            <span><i class="fa fa-clock-o"></i><?php echo $website_info[0]["submission_date"];?></span>

include - ROOT/plugins/Kuhuang/templates/Websites/view.php, line 430
Cake\View\View::_evaluate() - CORE/src/View/View.php, line 1184
Cake\View\View::_render() - CORE/src/View/View.php, line 1138
Cake\View\View::render() - CORE/src/View/View.php, line 769
Cake\Controller\Controller::render() - CORE/src/Controller/Controller.php, line 762
App\Controller\NewsController::view() - APP/Controller/NewsController.php, line 3938
Cake\Controller\Controller::invokeAction() - CORE/src/Controller/Controller.php, line 539
Cake\Controller\ControllerFactory::handle() - CORE/src/Controller/ControllerFactory.php, line 140
Cake\Controller\ControllerFactory::invoke() - CORE/src/Controller/ControllerFactory.php, line 115
Cake\Http\BaseApplication::handle() - CORE/src/Http/BaseApplication.php, line 317
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 77
Cake\Http\Middleware\CsrfProtectionMiddleware::process() - CORE/src/Http/Middleware/CsrfProtectionMiddleware.php, line 174
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\I18n\Middleware\LocaleSelectorMiddleware::process() - CORE/src/I18n/Middleware/LocaleSelectorMiddleware.php, line 61
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Http\Middleware\BodyParserMiddleware::process() - CORE/src/Http/Middleware/BodyParserMiddleware.php, line 157
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73

Notice: file_put_contents() [function.file-put-contents]: Write of 2421 bytes failed with errno=28 No space left on device in /www/wwwroot/www.adminso.com/vendor/cakephp/cakephp/src/Log/Engine/FileLog.php on line 140

Warning (2): Trying to access array offset on value of type null [ROOT/plugins/Kuhuang/templates/Websites/view.php, line 430]Code Context          <div class="info"> 
            <span><a href="<?php echo $website_info[0]["nsort"]["nsort_url"];?>"><i class="fa fa-columns"></i><?php echo $website_info[0]["nsort"]["nsort_name"];?></a></span> 
            <span><i class="fa fa-clock-o"></i><?php echo $website_info[0]["submission_date"];?></span> 
include - ROOT/plugins/Kuhuang/templates/Websites/view.php, line 430
Cake\View\View::_evaluate() - CORE/src/View/View.php, line 1184
Cake\View\View::_render() - CORE/src/View/View.php, line 1138
Cake\View\View::render() - CORE/src/View/View.php, line 769
Cake\Controller\Controller::render() - CORE/src/Controller/Controller.php, line 762
App\Controller\NewsController::view() - APP/Controller/NewsController.php, line 3938
Cake\Controller\Controller::invokeAction() - CORE/src/Controller/Controller.php, line 539
Cake\Controller\ControllerFactory::handle() - CORE/src/Controller/ControllerFactory.php, line 140
Cake\Controller\ControllerFactory::invoke() - CORE/src/Controller/ControllerFactory.php, line 115
Cake\Http\BaseApplication::handle() - CORE/src/Http/BaseApplication.php, line 317
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 77
Cake\Http\Middleware\CsrfProtectionMiddleware::process() - CORE/src/Http/Middleware/CsrfProtectionMiddleware.php, line 174
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\I18n\Middleware\LocaleSelectorMiddleware::process() - CORE/src/I18n/Middleware/LocaleSelectorMiddleware.php, line 61
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Http\Middleware\BodyParserMiddleware::process() - CORE/src/Http/Middleware/BodyParserMiddleware.php, line 157
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73

Notice: file_put_contents() [function.file-put-contents]: Write of 2445 bytes failed with errno=28 No space left on device in /www/wwwroot/www.adminso.com/vendor/cakephp/cakephp/src/Log/Engine/FileLog.php on line 140
">

Warning (2): Undefined array key "nsort" [ROOT/plugins/Kuhuang/templates/Websites/view.php, line 430]Code Context          <div class="info"> 
            <span><a href="<?php echo $website_info[0]["nsort"]["nsort_url"];?>"><i class="fa fa-columns"></i><?php echo $website_info[0]["nsort"]["nsort_name"];?></a></span> 
            <span><i class="fa fa-clock-o"></i><?php echo $website_info[0]["submission_date"];?></span> 
include - ROOT/plugins/Kuhuang/templates/Websites/view.php, line 430
Cake\View\View::_evaluate() - CORE/src/View/View.php, line 1184
Cake\View\View::_render() - CORE/src/View/View.php, line 1138
Cake\View\View::render() - CORE/src/View/View.php, line 769
Cake\Controller\Controller::render() - CORE/src/Controller/Controller.php, line 762
App\Controller\NewsController::view() - APP/Controller/NewsController.php, line 3938
Cake\Controller\Controller::invokeAction() - CORE/src/Controller/Controller.php, line 539
Cake\Controller\ControllerFactory::handle() - CORE/src/Controller/ControllerFactory.php, line 140
Cake\Controller\ControllerFactory::invoke() - CORE/src/Controller/ControllerFactory.php, line 115
Cake\Http\BaseApplication::handle() - CORE/src/Http/BaseApplication.php, line 317
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 77
Cake\Http\Middleware\CsrfProtectionMiddleware::process() - CORE/src/Http/Middleware/CsrfProtectionMiddleware.php, line 174
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\I18n\Middleware\LocaleSelectorMiddleware::process() - CORE/src/I18n/Middleware/LocaleSelectorMiddleware.php, line 61
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Http\Middleware\BodyParserMiddleware::process() - CORE/src/Http/Middleware/BodyParserMiddleware.php, line 157
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73

Warning (2): Trying to access array offset on value of type null [ROOT/plugins/Kuhuang/templates/Websites/view.php, line 430]Code Context          <div class="info"> 
            <span><a href="<?php echo $website_info[0]["nsort"]["nsort_url"];?>"><i class="fa fa-columns"></i><?php echo $website_info[0]["nsort"]["nsort_name"];?></a></span> 
            <span><i class="fa fa-clock-o"></i><?php echo $website_info[0]["submission_date"];?></span> 
include - ROOT/plugins/Kuhuang/templates/Websites/view.php, line 430
Cake\View\View::_evaluate() - CORE/src/View/View.php, line 1184
Cake\View\View::_render() - CORE/src/View/View.php, line 1138
Cake\View\View::render() - CORE/src/View/View.php, line 769
Cake\Controller\Controller::render() - CORE/src/Controller/Controller.php, line 762
App\Controller\NewsController::view() - APP/Controller/NewsController.php, line 3938
Cake\Controller\Controller::invokeAction() - CORE/src/Controller/Controller.php, line 539
Cake\Controller\ControllerFactory::handle() - CORE/src/Controller/ControllerFactory.php, line 140
Cake\Controller\ControllerFactory::invoke() - CORE/src/Controller/ControllerFactory.php, line 115
Cake\Http\BaseApplication::handle() - CORE/src/Http/BaseApplication.php, line 317
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 77
Cake\Http\Middleware\CsrfProtectionMiddleware::process() - CORE/src/Http/Middleware/CsrfProtectionMiddleware.php, line 174
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\I18n\Middleware\LocaleSelectorMiddleware::process() - CORE/src/I18n/Middleware/LocaleSelectorMiddleware.php, line 61
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Http\Middleware\BodyParserMiddleware::process() - CORE/src/Http/Middleware/BodyParserMiddleware.php, line 157
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73

一、sql中的groupby用法解析：　　GroupBy语句从英文的字面意义上理解就是“根据(by)一定的规则进行分组(Group)”。　　作用：通过一定的规则将一个数据集划分成若干个小的区域，然后针对若干个小区域进行数据处理

一、sql中的group by 用法解析：

　　Group By语句从英文的字面意义上理解就是“根据(by)一定的规则进行分组(Group)”。

　　作用：通过一定的规则将一个数据集划分成若干个小的区域，然后针对若干个小区域进行数据处理。

　　注意：group by 是先排序后分组！

　　举例说明：如果要用到group by 一般用到的就是“每”这个字，例如现在有一个这样的需求：查询每个部门有多少人。就要用到分组的技术　

select DepartmentID as '部门名称',COUNT(*) as '个数'　　from BasicDepartment　　group by DepartmentID

　　这个就是使用了group by +字段进行了分组，其中我们就可以理解为我们按照部门的名称ID
　　DepartmentID将数据集进行了分组；然后再进行各个组的统计数据分别有多少；

二、group by 和having 解释

　　前提：必须了解sql语言中一种特殊的函数——聚合函数。

　　例如：SUM, COUNT, MAX, AVG等。这些函数和其它函数的根本区别就是它们一般作用在多条记录上。

　　WHERE关键字在使用集合函数时不能使用，所以在集合函数中加上了HAVING来起到测试查询结果是否符合条件的作用。

　　having称为分组过滤条件，也就是分组需要的条件，所以必须与group by联用。

　　需要注意说明：当同时含有where子句、group by 子句、having子句及聚集函数时，执行顺序如下：

　　1、执行where子句查找符合条件的数据；

　　2、使用group by 子句对数据进行分组；

　　3、对group by 子句形成的组运行聚集函数计算每一组的值；

　　4、最后用having 子句去掉不符合条件的组。

　　having 子句中的每一个元素也必须出现在select列表中。有些数据库例外，如oracle.

　　having子句和where子句都可以用来设定限制条件以使查询结果满足一定的条件限制。

　　having子句限制的是组，而不是行。聚合函数计算的结果可以当条件来使用，where子句中不能使用聚集函数，而having子句中可以。

总结

以上所述是小编给大家介绍的SQL中的group by 和 having 用法，希望对大家有所帮助，如果大家有任何疑问请给我留言，小编会及时回复大家的。在此也非常感谢大家对脚本之家网站的支持！

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