Write 1 SQL query to combine 3 independent tables with functions: group by and case when - sql

Question

I have 3 tables as follows:
Table school_a with 4 columns:
date: (2020-11-31,...)
note: (20, 30, 40,...)
home: (23.45, 45.34, 65.67, ...)
id: (54326, 87332, ...)
Table school_b with 4 columns:
time: (2020-11-31,...)
grade: (34, 54, 34,...)
homework: (12.32, 34.65,...)
user: ('student', 'professor', 'student',...)
Table school_c with 4 columns:
day: (2020-11-31,...)
number: (34, 54, 34,...)
amount: (10.24 AGE, 11.25 AGE, 12.63 AGE, ...)
title: ('54934-ST-string-student-str.st', '54934-ST-string-teacher-str.st',....)
Sorry for the table presentation but it is not easy to put in a table format.
I created a SQL query to calculate what I need for each table but I do not succeed to combine the 3 queries in one. I cannot figure out the logic that I need to use to combine it.
Here is my SQL code for each table:
SELECT
SUM(home/note) AS kpi,
CASE
WHEN id IN (34564, 87423, 89076, 32145, 87653) THEN 'Student'
WHEN id IN (67543, 87413, 78996, 34215 ) THEN 'Teacher'
ELSE 'Other'
END AS role
FROM school_a
WHERE date >= '2020-08-01' AND date <= '2020-08-31'
GROUP BY role
SELECT
SUM(grade)/COUNT(user) AS kpi,
CASE
WHEN user = 'Student' THEN 'Student'
WHEN user = 'Professor' THEN 'Teacher'
ELSE 'Other'
END AS role
FROM school_b
WHERE time >= '2020-08-01' AND time <= '2020-08-31'
GROUP BY role
SELECT
SUM((REPLACE(amount,' AGE',''))/number) AS kpi,
CASE
WHEN title IN ('41320 - ST-STtr-Student-str.st', '89064 - ST-stRst-str-strr user-strr.str/blablabla/strstr') THEN 'Student'
WHEN title IN ('43789 - ST-STred-Teacher-stee.str', '65283-CH-strstrs-teacher-strr.str--STR') THEN 'Teacher'
ELSE 'Other'
END AS role
FROM school_c
WHERE day >= '2020-08-01' AND day <= '2020-08-31'
GROUP BY role
As you understand I need to measure the kpi for each table that have different columns names and different columns meaning for the full month of August 2020.
When I run separately each query I got what I need now I would like to combine all the 3 queries into one. If I create only one query I got a message such as
Error: ambiguous column name: role
Any feedback to improve my current queries is welcome. Thanks for reading.
----- Edited to clarify the result
The expected result is a table with 2 columns (role and kpi) and 3 rows (Student, Teacher, Other).
Using "union" I got almost what I want: 2 columns (role and kpi) and more than 3 rows as the grouping is school and then role. I want only the role and sum the kpi per role.

Answer 1

Have you tried to simply UNION the different outputs?
SELECT SUM(home/note) AS kpi,
CASE
WHEN id IN (34564, 87423, 89076, 32145, 87653) THEN 'Student'
WHEN id IN (67543, 87413, 78996, 34215 ) THEN 'Teacher'
ELSE 'Other'
END AS role
FROM school_a
WHERE date >= '2020-08-01' AND date <= '2020-08-31'
GROUP BY role
UNION
SELECT SUM(grade)/COUNT(user) AS kpi,
CASE
WHEN user = 'Student' THEN 'Student'
WHEN user = 'Professor' THEN 'Teacher'
ELSE 'Other'
END AS role
FROM school_b
WHERE time >= '2020-08-01' AND time <= '2020-08-31'
GROUP BY role
UNION
SELECT SUM((REPLACE(amount,' AGE',''))/number) AS kpi,
CASE
WHEN title IN ('41320 - ST-STtr-Student-str.st', '89064 - ST-stRst-str-strr user-strr.str/blablabla/strstr') THEN 'Student'
WHEN title IN ('43789 - ST-STred-Teacher-stee.str', '65283-CH-strstrs-teacher-strr.str--STR') THEN 'Teacher'
ELSE 'Other'
END AS role
FROM school_c
WHERE day >= '2020-08-01' AND day <= '2020-08-31'
GROUP BY role
I haven't done any checks in any way but as long as the columns match it shouldn't be a problem.