Combine tables

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

staffid	email	name	salary
0173	stan@bos.edu	Stern, Stan	99000
0101	ali@bos.edu	Aloof, Alison	30000

Table 2

id	fname	lname	gpa
1007	Peter	Perfect	590
1008	Donald	Dunce	220

Table 3

id	name	email	salary	gpa	species
F173	Stern,Stan	stan@bos.edu	99000		Staff
F101	Aloof,Alison	ali@bos.edu	30000		Staff
S1007	Perfect,Peter	1007@bos.edu		590	Student
S1008	Dunce,Donald	1008@bos.edu		220	Student

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

SQL HACKS

Hack 10 Converting subqueries into joins

Hack 11 Converting aggregate subqueries into joins

Hack 14 Generate Combinations

Hack 16 Search for a String across columns

Hack 24 Multiply Across a Result Set

Hack 25 Keep a running total

Hack 25.5 Splitting and combining columns

Hack 26 Include the rows your JOIN forgot

Hack 30 Calculate the maximum/minimum of two fields

Hack 33 Get values and subtotals in one shot

Hack 50 Combine tables containing different data

Hack 51/52 Display rows as columns

Hack 55 Import Someone Else's Data

Hack 62 Issue Queries Without Using a Table

Hack 63 Generate rows without tables

Hack 70 Combine your queries

Hack 72 Extract a subset of the results

Hack 78 Break it down by Range

Hack 88 Test two values from a subquery

Hack 98 Find and stop long running queries

Hack 100 Run SQL from a Web Page