我是Laravel的新手，如何使用Eloquent模型在Laravel中进行此查询：
SELECT
(
SELECT departments.deptname FROM school.counts
LEFT JOIN reference.departments
ON counts.departmentcode = department.departmentcode
WHERE counts.countid = a.countsid
) AS departmentDesc
FROM school.subjecthdr a
LEFT JOIN school.subjectdtls b
ON a.subjectid = b.subjectid;
我不想使用原始查询，有什么办法吗？我仍然感谢原始查询建议（如果有）。
我认为您仍然需要一些原始查询。
$dept_desc = \DB::table('school.counts')
->leftjoin('reference.departments','counts.departmentcode','=','departments.departmentcode')
->whereRaw('counts.countid = a.countsid')
->selectRaw('departments.deptname');
\DB::table('school.subjecthdr AS a')
->leftjoin('subjectdtls AS b','a.subjectid','b.subjectid')
->selectRaw('(' . $dept_desc->toSql() . ') AS departmentDesc')
->get();
PS：我认为您leftjoin subjectdtls b，但看来您不需要它。
如果您要使用Eloquent\Builder，则不仅要使用一个数据库，
您需要执行以下操作：
How to use multiple databases in Laravel