如何使用 Laravel 查询生成器从联合结果中获取最小值或最大值？答案

【问题标题】：How Can I get Min or Max value from Union result with Laravel Query Builder?如何使用 Laravel 查询生成器从联合结果中获取最小值或最大值？
【发布时间】：2018-09-19 06:34:06
【问题描述】：

我想从联合表中获取最小值。

如下所示的 MySQL 查询。

SELECT MIN(PromisedDate) 
FROM (SELECT PromisedDate FROM JobWorkOrder WHERE `PromisedDate` IS NOT NULL
    UNION
    SELECT ScheduledDate AS PromisedDate FROM JobPhase WHERE `ScheduledDate` IS NOT NULL) ScheduledTable;

此查询的结果是 JobWorkOrder 和 JobPhase 表中 PromisedDate 和 ScheduledDate 的最小值。

所以我构建了一个如下所示的 Laravel 查询。

$JobPhase = JobPhase::where('ScheduledDate', '<>', null)
    ->select('ScheduledDate AS PromisedDate');

$minDate = JobWorkOrder::where('PromisedDate', '<>', null)
    ->select('PromisedDate')
    ->union($JobPhase)
    ->min('PromisedDate');

但是我得到了错误的结果。结果是

(SELECT MIN(`PromisedDate`) FROM `JobWorkOrder` WHERE `PromisedDate` IS NOT NULL) 
union 
(SELECT `ScheduledDate` AS `PromisedDate` FROM `JobPhase` WHERE `ScheduledDate` IS NOT NULL)

如何构建 Laravel 查询？

【问题讨论】：

标签： laravel-5

【解决方案1】：

您可以从 get() 函数结果中获取 min。只需在查询中添加一个 get() 函数即可。

$JobPhase = JobPhase::where('ScheduledDate', '<>', null)
    ->select('ScheduledDate AS PromisedDate');

$minDate = JobWorkOrder::where('PromisedDate', '<>', null)
    ->select('PromisedDate')
    ->union($JobPhase)
    ->get()
    ->min('PromisedDate');

然后你会得到一个 MIN 值。

【讨论】：

【解决方案2】：

min 字段是从子查询中选择的：

$JobPhase = JobPhase::where('ScheduledDate', '<>', null)
    ->select('ScheduledDate AS PromisedDate');

$sub = $JobWorkOrder = JobWorkOrder::where('PromisedDate', '<>', null)
    ->select('PromisedDate')
    ->union($JobPhase);

$minDate = DB::table( DB::raw("({$sub->toSql()}) as sub") )
    ->mergeBindings($sub->getQuery())
    ->min('PromisedDate');

另请参阅：How to select from subquery using Laravel Query Builder?

【讨论】：