Delete Rows with Duplicate Column Data in Specific Columns - sql

Question

I have a table we'll call Table1 with a bunch of junk data in it and no unique identifier column.
I want to select some columns from Table1 and transfer the data to Table2. However, after the transfer, I need to delete rows from Table2 with duplicates in 3 of the columns.
Let's say I have a row in Table2 with columns [FirstName], [LastName], [CompanyName], [City], and [State] that were transferred. I want only the rows with unique combinations of [FirstName], [LastName], and [CompanyName] to remain. To add to the confusion, [LastName] and/or [CompanyName] could contain NULL values. How could I accomplish this? Thanks in advance for any help.

Answer 1

Unique entries can be created using the distinct keyword.
select distinct
FirstName,
LastName,
CompanyName
from MyTable
So if you issue the following command, you will only add distinct values to the new table
insert into newTable
(
FirstName,
LastName,
CompanyName
)
select distinct
FirstName,
LastName,
CompanyName
from MyTable
where not exists (
select 1 from newTable
where newTable.FirstName = MyTable.FirstName
and newTable.LastName = MyTable.LastName
and newTable.CompanyName = MyTable.CompanyName
)
Another nice way to add distinct new values to a table can be done by using the 'MERGE' command.
merge newtable as target
using (select distinct
FirstName,
LastName,
CompanyName
from MyTable
) as source
on target.FirstName = target.FirstName
and target.LastName = target.LastName
and target.CompanyName = target.CompanyName
when not matched by target then
insert (FirstName,
LastName,
CompanyName)
values (target.FirstName,
target.LastName,
target.CompanyName);
The MERGE command gives you the option to control when you want to synchronize tables.

Answer 2

see here example , might be this is what you wanted..link
insert into Table2(`firstname` , `lastname` , `companyname`)
select a.firstname,a.lastname,a.companyname
from
(select distinct(concat(firstname,',',lastname,',',companyname))
,firstname,lastname,companyname from Table1) a;

Answer 3

create table t2
as
select distinct FirstName,LastName,CompanyName,City,State from t1;
with the below query u 'll get to know we have duplicate entries or not.
select FirstName,LastName,CompanyName,count(*) from t2
group by FirstName,LastName,CompanyName
having Count(*) >1;
delete from t2 a where rowid not in (select min(rowid) from t2 b where a.column1=b.column1
and .....);