Combine tables

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Combine tables containing different data.

In this example you are shown how to take tables with different data and put them into a single table

that is more understandable allowing all the information from two or more tables to be seen.

Table 1 and table 2 show the two tables you want to combine and table 3 is the table they are combined into.

Table 1
staffidemailnamesalary
0173stan@bos.eduStern, Stan99000
0101ali@bos.eduAloof, Alison30000
Table 2
idfnamelnamegpa
1007PeterPerfect590
1008DonaldDunce220
Table 3
idnameemailsalarygpaspecies
F173Stern,Stanstan@bos.edu99000Staff
F101Aloof,Alisonali@bos.edu30000Staff
S1007Perfect,Peter1007@bos.edu590Student
S1008Dunce,Donald1008@bos.edu220Student
schema:scott
DROP TABLE staff;
DROP TABLE student;
 CREATE TABLE staff(
  staffid INTEGER,
  email VARCHAR(20),
  name VARCHAR(20),
  salary INTEGER );
INSERT INTO staff VALUES (0173,'stan@bos.edu','Stern, Stan',99000);
INSERT INTO staff VALUES (0101,'ali@bos.edu','Aloof, Alison',30000);
CREATE TABLE student (
  id INTEGER,
  fname VARCHAR(20),
  lname VARCHAR(20),
  gpa INTEGER );
INSERT INTO student VALUES (1007,'Peter','Perfect',590);
INSERT INTO student VALUES (1008,'Donald','Dunce',220);

You can use UNION when you have two tables you want to combine but that contain different data.

You will have to make the two tables agree before you can do the UNION though, this is done by making the final table contain all information from all tables with NULL entries in the rows that don't have the data required.

In this example a staff table and a student table are combined.

SELECT 'F' || staffid id, name name,
email email, salary salary, NULL gpa, 'Staff' species
  FROM staff
  UNION
  SELECT 'S' || id id, lname || ',' || fname name,
id || '@bos.edu' email, NULL salary, gpa gpa,
'Student' species
    FROM student
SELECT 'F' || staffid id, name name,
email email, salary salary, NULL gpa, 'Staff' species
  FROM staff
  UNION
  SELECT 'S' || id id, lname || ',' || fname name,
id || '@bos.edu' email, NULL salary, gpa gpa,
'Student' species
    FROM student
SELECT CONCAT('F',staffid) id, name name,
email email, salary salary, NULL gpa, 'Staff' species
  FROM staff
  UNION
  SELECT CONCAT('S',id) id, CONCAT(lname,',',fname) name,
CONCAT(id,'@bos.edu') email, NULL salary, gpa gpa,
'Student' species
    FROM student
SELECT 'F' + staffid id, name name,
email email, salary salary, NULL gpa, 'Staff' species
  FROM staff
  UNION
  SELECT 'S' + id id, lname + ',' + fname name,
id + '@bos.edu' email, NULL salary, gpa gpa,
'Student' species
    FROM student
SELECT 'F' + staffid id, name name,
email email, salary salary, NULL gpa, 'Staff' species
  FROM staff
  UNION
  SELECT 'S' + id id, lname + ',' + fname name,
id + '@bos.edu' email, NULL salary, gpa gpa,
'Student' species
   FROM student
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