如何在SQL Alchemy中结合CASE和EXISTS？

Question

例如：

SELECT 
  CASE WHEN EXISTS (
    SELECT 
      * 
    FROM 
      "Teaching"
    WHERE 
      "Teaching".student_idn = "Student".idn
  ) THEN 'Teaching Assistant' ELSE 'Student' END AS "Category" 
FROM 
  "Student"

如何在SQL Alchemy中编写？我能够弄清楚CASE是如何完成的。但是当我们需要EXISTS

时，它变得越来越复杂

Answer 1

以下方法有效：

sub = session.query(Teaching).filter(Teaching.columns.student_idn == Student.columns.idn)

query = session.query(Student.columns.name, case([(sub.exists(), "Teaching Assistant")], else_ = "Student")
)

可能有更好的方法。