聚合
在模型中也可以调用数据库的聚合方法进行查询，例如：
| 方法 | 说明 |
|---|---|
| count | 统计数量，参数是要统计的字段名（可选） |
| max | 获取最大值，参数是要统计的字段名（必须） |
| min | 获取最小值，参数是要统计的字段名（必须） |
| avg | 获取平均值，参数是要统计的字段名（必须） |
| sum | 获取总分，参数是要统计的字段名（必须） |
count
<?php
$user = new User();
$user->count();
// SELECT COUNT(*) as count FROM `easyswoole_user` LIMIT 1
$user->count('id', 'name');
// SELECT COUNT(id) as count FROM `easyswoole_user` GROUP BY name LIMIT 1
$user->queryLimit()->fields(['id', 'name']);
$user->count(null, 'name');
// SELECT COUNT(`id`) as id, COUNT(`name`) as name FROM `easyswoole_user` GROUP BY name LIMIT 1max
$user = new User();
$user->max('id');
// SELECT MAX(`id`) as id FROM `easyswoole_user` LIMIT 1
$user->max('id', 'name');
// SELECT MAX(`id`) as id FROM `easyswoole_user` GROUP BY name LIMIT 1
$user->max(['id', 'name'], 'name');
// SELECT MAX(`id`) as id , MAX(`name`) as name FROM `easyswoole_user` GROUP BY name LIMIT 1min
<?php
$user = new User();
$user->min('id');
// SELECT MIN(`id`) as id FROM `easyswoole_user` LIMIT 1
$user->min('id', 'name');
// SELECT MIN(`id`) as id FROM `easyswoole_user` GROUP BY name LIMIT 1
$user->min(['id', 'name'], 'name');
// SELECT MIN(`id`) as id , MIN(`name`) as name FROM `easyswoole_user` GROUP BY name LIMIT 1avg
<?php
$user = new User();
$user->avg('id');
// SELECT AVG(`id`) as id FROM `easyswoole_user` LIMIT 1
$user->avg('id', 'name');
// SELECT AVG(`id`) as id FROM `easyswoole_user` GROUP BY name LIMIT 1
$user->avg(['id', 'name'], 'name');
// SELECT AVG(`id`) as id , AVG(`name`) as name FROM `easyswoole_user` GROUP BY name LIMIT 1sum
<?php
$user = new User();
$user->sum('id');
// SELECT SUM(`id`) as id FROM `easyswoole_user` LIMIT 1
$user->sum('id', 'name');
// SELECT SUM(`id`) as id FROM `easyswoole_user` GROUP BY name LIMIT 1
$user->sum(['id', 'name'], 'name');
// SELECT SUM(`id`) as id , SUM(`name`) as name FROM `easyswoole_user` GROUP BY name LIMIT 1