how to load specific attributes from two table to another? - sql

Question

I am trying to load attributes from two tables to one table.
I have a Location table:
Id City State Country
===============================
1 New York New York USA
2 Portland Oregon USA
3 Tokyo Honshu Japan
And a User table:
Id First_Name Last_Name Hometown_City Hometown_State Hometown_Country
===========================================================================
1 Brett Burr New York New York USA
2 Bucky Beaver Portland Oregon USA
3 Ranma Saotome Tokyo Honshu Japan
I'm creating a new table for users, which instead of containing the separate Hometown fields, has a Hometown_Id foreign key.
Something like:
Id First_Name Last_Name Hometown_Id
========================================
1 Brett Burr 1
2 Bucky Beaver 2
3 Ranma Saotome 3
However, I'm having a problem with the syntax when inserting the data into the new Users table.
I can insert the non-location based fields easily with a command like:
INSERT INTO newusers (Id, First_Name, Last_Name)
SELECT DISTINCT Id, First_Name, Last_Name
FROM users
However, I'm not sure of the correct syntax to then add the values from the location table

Answer 1

Assuming that you have the appropriate constraints, and that the Location table contains unique entries, the following should work:
INSERT INTO newusers (Id, First_Name, Last_Name, Hometown_Id)
SELECT users.Id, users.First_Name, users.Last_Name, locations.Id
FROM users
INNER JOIN locations
ON locations.City = users.Hometown_City
AND locations.State = users.Hometown_State
AND locations.Country = users.Hometown_Country
If you have more than one location needed (such as a 'current residence' entry), alias and join to the locations table (from users) a second time.