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.