Union ,Union All in Sql (Set Operators )

Union ,Union All in Sql (Set Operators ).
keywords: union and union all,union,union all

Table Scripts:
create table PermanantCustomer
(
CustomerId int,
Name varchar(100),
Country varchar(100)
)

insert into PermanantCustomer values(1,'Arun','India')
insert into PermanantCustomer values(2,'kumar','India')
insert into PermanantCustomer values(3,'Sara','Uk')

create table TemporaryCustomer
(
CustomerId int,
Name varchar(100),
Country varchar(100)
)

insert into TemporaryCustomer values(1,'Sajan','UK')
insert into TemporaryCustomer values(2,'kumar','India')
insert into TemporaryCustomer values(3,'Meera','India')


--Set Operators
---Union and Union All
--combine multiple table data to one result set
select * from PermanantCustomer
select * from TemporaryCustomer

--union all
--union all contains all records include duplicate also
select * from PermanantCustomer
union all
select * from TemporaryCustomer

--no of columns and datatype must be same in case of union and union all

--not allowed first result set 2 column and second result set 3 columns
select CustomerId,Name from PermanantCustomer
union all
select CustomerId,Name,Country from TemporaryCustomer

--not allowed first result customerid datatype int,second result set name column datatype varchar

select Name,CustomerId,Country from PermanantCustomer
union all
select CustomerId,Name,Country from TemporaryCustomer

--Allowed
select CustomerId,Name,Country from PermanantCustomer
union all
select CustomerId,Name,Country from TemporaryCustomer


--order by clause will be used for last select query

select * from PermanantCustomer
union all
select * from TemporaryCustomer
order by CustomerId


--union removes duplicate records and sort data

select * from PermanantCustomer
union
select * from TemporaryCustomer

--we can use seperate order by clause also
--sort by name
select * from PermanantCustomer
union
select * from TemporaryCustomer
order by name


--performance

--union = slow performance compared to union all because need to find duplicate and remove that rows and sort data
--union all=better performace no need to remove duplicates.


Regards,
Sql Query for jobs
#https://www.youtube.com/@SqlQueryforjobs


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