How can I have UNION respect column aliases? - sql

Question

Sorry for the bad title, I couldn't think of anything better. Feel free to edit.
I have to work with a db table that uses one column to store different types of information (last name if person, company name if company). A nightmare, I know, but it's what it is.
To distinguish the meaning, there is another column with an integer that specifies the type of what's in the name column.
The schema of this table looks as follows (simplified):
ID int
dtype int
name varchar(50)
So, a sample could look like this:
ID dtype name
---------------------------
1 0 Smith
2 0 Trump
3 1 ABC Ltd.
4 1 XYZ Ltd.
I'm trying to normalize this using the following T-SQL code:
WITH companies AS
(
SELECT ID, name AS company
FROM nametable WHERE dtype=1
),
people AS
(
SELECT ID, name AS person
FROM nametable WHERE dtype=0
),
SELECT * FROM companies UNION ALL SELECT * FROM people;
What I hoped to get is a new table with the schema:
ID
dtype
company
person
Or, in table view:
ID dtype person company
------------------------------------------
1 0 Smith
2 0 Trump
3 1 ABC Ltd.
4 1 XYZ Ltd.
Instead, the field is now just called person instead of name but it's still just one field for 2 types of information.
I understand I could just create a new table and insert each partial result into it but it seems there should be a simpler way. Any advice appreciated.

Answer 1

It seems you need case when which helps you
select ID, dtype,case when dtype=0 then name end AS company,
case when dtype=1 then name end AS person
FROM nametable
The CASE statement goes through conditions and return a value when condition is met, from your sample input and output its clear you want to create type wise new column ,so i used case Statement

Answer 2

You don't need to use UNION for this at all. A better approach would be using a bit of aggregation.
SELECT ID,
MAX(CASE WHEN dtype = 0 THEN [name] END) AS company
MAX(CASE WHEN dtype = 1 THEN [name] END) AS person
FROM nametable
GROUP BY ID;
UNION (ALL) doesn't "care" for aliases though. It combines the datasets it receives into 1. All the datasets must have the same definition and the dataset returned will have the same definition. If the datasets have different aliases for columns, the aliases supplied in the first dataset will be used. UNION doesn't detect that the datasets have different names for the columns and therefore return the different names as different columns; that's not what a UNION does.
Edit: well this will give the OP the data they want, however, there's no need for the aggregation. I was honestly expected ID's to be a shared resource; because that's normally the only time you have such horrid tables. The fact that it isn't just makes this table even more confused...