Inserting unique value from another table - sql

Question

Tables: I have 3 tables
They are cust, new_cust, old_cust
all of them have 3 columns, they are id, username, name
each of them have possibilities to have same data as the others.
I would like to make "whole" table that consisting all of them but only the uniques.
I've Tried
Creating a dummy table
I've tried to create the dummy table called "Temp" table by
select *
into Temp
from cust
insert all table to dummy
Then I insert all of them into they Temp table
insert into temp
select * from new_cust
insert into temp
select * from old_cust
taking uniques using distinct
After they all merged I'm using distinct to only take the unique id value
select distinct(id), username, fullname
into Whole
from temp
it did decreasing some rows
Result
But after I move it to whole table I would like to put primary key on id but I got the message that there are some duplicate values. Is there any other way?

Answer 1

I am guessing that you want unique ids. And you want these prioritized by the tables in some order. If so, you can do this with union all and row_number():
select id, username, name
from (select c.*,
row_number() over (partition by id order by priority) as seqnum
from ((select id, username, name, 1 as priority
from new_cust
) union all
(select id, username, name, 2 as priority
from cust
) union all
(select id, username, name, 3 as priority
from old_cust
)
) c
) c
where seqnum = 1;

Answer 2

Try this:
insert into temp
select * from new_cust
UNION
select * from old_cust
Union will avoid the duplicate entries and you can then create a primary key on ID column

Answer 3

Try this below query...
WITH cte as (
SELECT id, username, NAME,
ROW_NUMBER() OVER (PARTITION BY t1.id ORDER BY t1.username, t1.name ) AS rn
FROM cust t1
LEFT JOIN new_cust t2 ON t1.Id = t2.Id
LEFT JOIN old_cust t3 ON t2.Id = t3.Id
)
SELECT id, username, NAME
FROM cte
WHERE rn = 1
Note:-
Put all the query inside a CTE(Common table expression)
with a new column(rn) that you will use to filter the results.
This new Column will produce ROW_NUMBER()....PARTITION BY username,name.....

Answer 4

But after I move it to whole table I would like to put primary key on
id but I got the message that there are some duplicate values.?
That's because You are trying to insert ID value from each of the tables to Whole table.
Just insert username and name and skip ID. ID is IDENTITY and it MUST be unique.
Run this on Your current Whole table to see if You have duplicated Id's:
select COUNT(ID), username
from whole
GROUP BY username
HAVING COUNT(ID) > 1
To get unique customers recreate table Whole and make ID col IDENTITY:
IF OBJECT_ID ('dbo.Whole') IS NOT NULL DROP TABLE dbo.Whole;
CREATE TABLE Whole (ID INT NOT NULL IDENTITY(1,1), Name varchar(max), Username varchar(max))
Insert values into Whole table:
INSERT INTO Whole
SELECT Name, Username FROM cust
UNION
SELECT Name, Username FROM new_cust
UNION
SELECT Name, Username FROM old_cust
Make ID col PK.

Answer 5

What does Unique mean for your row ?
If it is only the username, and you don't care about keeping the old ID values,
this will favor the new_cust data over the old_cust data.
SELECT
ID = ROW_NUMBER() OVER (ORDER BY all_temp.username)
, all_temp.*
INTO dbo.Temp
FROM
(
SELECT nc.username, nc.[name] FROM new_cust AS nc
UNION
SELECT oc.username, oc.[name]
FROM old_cust AS oc
WHERE oc.username NOT IN (SELECT nc1.username FROM new_cust AS nc1) --remove the where part if needed
) AS all_temp
ALTER TABLE dbo.Temp ALTER COLUMN ID INTEGER NOT NULL
ALTER TABLE dbo.Temp ADD PRIMARY KEY (ID)
If by Unique you mean both the username and name then just remove the where part in the union