[SQL][sqlzoo] Using Null

Using Null                                                                                                                    

Using Null - SQLZOO

1.NULL, INNER JOIN, LEFT JOIN, RIGHT JOIN

SELECT name
FROM teacher
WHERE dept IS NULL

2.

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)

3.

Use a different JOIN so that all teachers are listed.

SELECT teacher.name, dept.name
FROM teacher 
INNER JOIN dept ON (teacher.dept=dept.id)

4.

Use a different JOIN so that all departments are listed.

SELECT teacher.name, dept.name
FROM teacher
LEFT JOIN dept ON (teacher.dept = dept.id)

5.

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') 
FROM teacher

6.

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')
FROM teacher
LEFT JOIN dept ON teacher.dept = dept.id

7.

Use COUNT to show the number of teachers and the number of mobile phones.

SELECT COUNT(teacher.id) ,COUNT(mobile) 
FROM teacher

8.

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 dept.name, COUNT(teacher.id) 
FROM teacher
RIGHT JOIN dept ON teacher.dept = dept.id
GROUP BY dept.name

9.

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 teacher.name,CASE WHEN dept IS NULL THEN 'Art' ELSE 'Sci' END 
FROM teacher

10.

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 teacher.name,
  CASE
    WHEN dept IS NULL THEN 'None'
    WHEN dept = 3 THEN 'Sci'
    ELSE 'Sci'
  END 
FROM teacher

Using Null Quiz                                                                                                                    

1.

 SELECT teacher.name, dept.name FROM teacher LEFT OUTER JOIN dept ON (teacher.dept = dept.id)

2.

 SELECT dept.name FROM teacher JOIN dept ON (dept.id = teacher.dept) WHERE teacher.name = 'Cutflower'

3.

 SELECT dept.name, COUNT(teacher.name) FROM teacher RIGHT JOIN dept ON dept.id = teacher.dept GROUP BY dept.name

4.

display 0 in result column for all teachers without department

5.

'four' for Throd

6.

Table-A

Shrivell	Computing
Throd	Computing
Splint	Computing
Spiregrain	Other
Cutflower	Other
Deadyawn	Other