Teacher - Dept Tables
teacher
101
1
Shrivell
07986 555 1234
102
1
Throd
07122 555 1920
103
1
Splint
104
Spiregrain
105
2
Cutflower
07996 555 6574
106
Deadyawn
...
dept
1
Computing
2
Design
3
Engineering
...
Teachers and Departments
The school includes many departments. Most teachers work exclusively for a single department. Some teachers have no department.
NULL, INNER JOIN, LEFT JOIN, RIGHT JOIN
List the teachers who have NULL for their department.
SELECT name FROM teacher WHERE dept IS NULL
Note the INNER JOIN misses the teachers with no department and the departments with no teacher.
SELECT teacher.name, dept.name
FROM teacher
INNER JOIN dept ON (teacher.dept=dept.id)
Use a different JOIN so that all teachers are listed.
SELECT teacher.name, dept.name
FROM teacher
LEFT JOIN dept ON (teacher.dept=dept.id)
Use a different JOIN so that all departments are listed.
SELECT teacher.name, dept.name
FROM teacher
RIGHT JOIN dept ON (teacher.dept=dept.id)
Use COALESCE to print the mobile number. Use the number '07986 444 2266' if there is no number given. Show teacher name and mobile number or '07986 444 2266'
SELECT name, COALESCE(mobile,'07986 444 2266') AS mobile
FROM teacher
Use the COALESCE function and a LEFT JOIN to print the teacher name and department name. Use the string 'None' where there is no department.
SELECT teacher.name, COALESCE(dept.name, 'None') AS dept
FROM teacher
LEFT JOIN dept ON (teacher.dept=dept.id)
Use COUNT to show the number of teachers and the number of mobile phones.
SELECT COUNT(name) AS num_teacher, COUNT(mobile) AS num_mobile
FROM teacher
Use COUNT and GROUP BY dept.name to show each department and the number of staff. Use a RIGHT JOIN to ensure that the Engineering department is listed.
SELECT d.name, COUNT(t.name) AS num_teacher
FROM teacher t
RIGHT JOIN dept d
ON t.dept = d.id
GROUP BY d.name
Use CASE to show the name of each teacher followed by 'Sci' if the teacher is in dept 1 or 2 and 'Art' otherwise.
SELECT
name,
CASE
WHEN (dept = 1 OR dept = 2) THEN 'Sci'
ELSE 'Art'
END AS new_name
FROM teacher
Use CASE to show the name of each teacher followed by 'Sci' if the teacher is in dept 1 or 2, show 'Art' if the teacher's dept is 3 and 'None' otherwise.
SELECT
name,
CASE
WHEN (dept = 1 OR dept = 2) THEN 'Sci'
WHEN dept = 3 THEN 'Art'
ELSE 'None'
END
FROM teacher
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