MySQL Multiple Joins in one query?

I have the following query:

SELECT dashboard_data.headline, dashboard_data.message, dashboard_messages.image_id FROM dashboard_data INNER JOIN dashboard_messages ON dashboard_message_id = dashboard_messages.id 

So I am using an INNER JOIN and grabbing the image_id. So now, I want to take that image_id and turn it into images.filename from the images table.

How can I add that in to my query?

4 Answers

You can simply add another join like this:

SELECT dashboard_data.headline, dashboard_data.message, dashboard_messages.image_id, images.filename FROM dashboard_data INNER JOIN dashboard_messages ON dashboard_message_id = dashboard_messages.id INNER JOIN images ON dashboard_messages.image_id = images.image_id 

However be aware that, because it is an INNER JOIN, if you have a message without an image, the entire row will be skipped. If this is a possibility, you may want to do a LEFT OUTER JOIN which will return all your dashboard messages and an image_filename only if one exists (otherwise you'll get a null)

SELECT dashboard_data.headline, dashboard_data.message, dashboard_messages.image_id, images.filename FROM dashboard_data INNER JOIN dashboard_messages ON dashboard_message_id = dashboard_messages.id LEFT OUTER JOIN images ON dashboard_messages.image_id = images.image_id 

Just add another join:

SELECT dashboard_data.headline, dashboard_data.message, dashboard_messages.image_id, images.filename FROM dashboard_data INNER JOIN dashboard_messages ON dashboard_message_id = dashboard_messages.id INNER JOIN images ON dashboard_messages.image_id = images.image_id 

I shared my experience of using two LEFT JOINS in a single SQL query.

I have 3 tables:

Table 1) Patient consists columns PatientID, PatientName

Table 2) Appointment consists columns AppointmentID, AppointmentDateTime, PatientID, DoctorID

Table 3) Doctor consists columns DoctorID, DoctorName

Query:

SELECT Patient.patientname, AppointmentDateTime, Doctor.doctorname FROM Appointment LEFT JOIN Doctor ON Appointment.doctorid = Doctor.doctorId //have doctorId column common LEFT JOIN Patient ON Appointment.PatientId = Patient.PatientId //have patientid column common WHERE Doctor.Doctorname LIKE 'varun%' // setting doctor name by using LIKE AND Appointment.AppointmentDateTime BETWEEN '1/16/2001' AND '9/9/2014' //comparison b/w dates ORDER BY AppointmentDateTime ASC; // getting data as ascending order 

I wrote the solution to get date format like "mm/dd/yy" (under my name "VARUN TEJ REDDY")

Multi joins in SQL work by progressively creating derived tables one after the other. See this link explaining the process: