連接3個表並顯示記錄，即使第3個表缺少值

Question

我想用此查詢聯接三個表：

select *, max(working_dx.date_added), diagnosis_list.diagnosis as WorkingDiagnosis from working_dx 
    inner join ild on ild.id_incr=working_dx.pt_id
    inner join diagnosis_list on working_dx.dx_id = diagnosis_list.id
    group by pt_id";

我想要ild表中的所有記錄，即使working_dx中沒有匹配的記錄-如果不匹配，WorkingDiagnosis中的值將只是空白。

上面的查詢只給我提供了work_dx.dx_id有值的記錄。 我如何執行JOIN語句將所有記錄返回給我，即使它們為空。

Answer 1

嘗試這個：

SELECT *, max(working_dx.date_added), 
(CASE WHEN diagnosis_list.id IS NULL THEN  "" ELSE diagnosis_list.diagnosis  END) as WorkingDiagnosis 
    FROM working_dx 
    INNER JOIN ild on ild.id_incr=working_dx.pt_id
    LEFT JOIN diagnosis_list on working_dx.dx_id = diagnosis_list.id
    GROUP BY pt_id;