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Abdullah Jassim
4,551 PointsOnce the two functions: Fifth and Seventh are created, instead of using inner join, why cant we use Union ALL?
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1 Answer
Ryan Dainton
17,164 Points SELECT STUDENTS.ID, STUDENTS.FIRST_NAME, STUDENTS.LAST_NAME
FROM CLASSES
JOIN SUBJECTS ON CLASSES.SUBJECT_ID = SUBJECTS.ID
JOIN SCHEDULE ON CLASSES.ID = SCHEDULE.CLASS_ID
JOIN STUDENTS ON SCHEDULE.STUDENT_ID = STUDENTS.ID
WHERE SUBJECTS.NAME = 'Science' AND PERIOD_ID = '5'
INTERSECT
SELECT STUDENTS.ID, STUDENTS.FIRST_NAME, STUDENTS.LAST_NAME
FROM CLASSES
JOIN SUBJECTS ON CLASSES.SUBJECT_ID = SUBJECTS.ID
JOIN SCHEDULE ON CLASSES.ID = SCHEDULE.CLASS_ID
JOIN STUDENTS ON SCHEDULE.STUDENT_ID = STUDENTS.ID
WHERE SUBJECTS.NAME = 'Art' AND PERIOD_ID = '7';
As the other Ryan said, UNION ALL will combine the two sets. However, I found INTERSECT to work, as it only gives the students common to both data sets (i.e. just Bobby Tables)
Ryan Colmon
Courses Plus Student 13,791 PointsRyan Colmon
Courses Plus Student 13,791 PointsUnion ALL combines both queries into one big list, so you would have a list of all students who either have 5th period science OR 7th period art. With the inner join it looks only for the records that are in both queries and disregards the rest.