There are 3 tables:
I would like to find out the average age of patients for each specialty .
SELECT specialty, AVG(year(curdate()) - year(patients.DOB))
FROM medics, patients, visits
WHERE medics.IDM = visits.medics GROUP by specialty;
The query above shows me on each line the average of all patients.
Try it:
SELECT
Speciality,
ROUND(AVG(YEAR(NOW())-YEAR(DOB)),0) AS Years
FROM visits
INNER JOIN medics
ON visits.IdMedic = medics.Id
INNER JOIN patients
ON visits.IdPatient = patients.Id
GROUP BY Speciality
My tables:
CREATE TABLE `visits` (
`Id` int(11) NOT NULL,
`IdMedic` int(11) DEFAULT NULL,
`IdPatient` int(11) DEFAULT NULL,
PRIMARY KEY (`Id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
CREATE TABLE `patients` (
`Id` int(11) NOT NULL,
`Name` varchar(45) DEFAULT NULL,
`DOB` date DEFAULT NULL,
PRIMARY KEY (`Id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
CREATE TABLE `medics` (
`Id` int(11) NOT NULL,
`Name` varchar(45) DEFAULT NULL,
`Speciality` varchar(45) DEFAULT NULL,
PRIMARY KEY (`Id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
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