Duplicates using distinct operator
I have below tables.
create table html_details(A int,b int,c int,d nvarchar(4))
create table pdf_details(A int,b int,c int,d nvarchar(4))
insert into pdf_details values(1,2,3,'pdf')
insert into pdf_details values(1,2,3,'pdf')
insert into pdf_details values(4,5,6,'pdf')
insert into html_details values(1,2,3,'html')
insert into html_details values(1,2,3,'html')
insert into html_details values(4,5,6,'html')
now i am using below query to avoid duplication in each tables.
select distinct a,b,c,d from html_details
union all
select distinct a,b,c,d from pdf_details
but above query gives poor performance because of distinct function in both query.so i am using distinct in outer query.Now performance is improved, but will it give same output?Both query are same in logic?
select distinct a,b,c,d from (
select a,b,c,d from html_details
union all
select a,b,c,d from pdf_details
)a
sql-server-2012 distinct-values
asked Dec 29 '18 at 16:04
RamRam
1578
add a comment |
I have below tables.
create table html_details(A int,b int,c int,d nvarchar(4))
create table pdf_details(A int,b int,c int,d nvarchar(4))
insert into pdf_details values(1,2,3,'pdf')
insert into pdf_details values(1,2,3,'pdf')
insert into pdf_details values(4,5,6,'pdf')
insert into html_details values(1,2,3,'html')
insert into html_details values(1,2,3,'html')
insert into html_details values(4,5,6,'html')
now i am using below query to avoid duplication in each tables.
select distinct a,b,c,d from html_details
union all
select distinct a,b,c,d from pdf_details
but above query gives poor performance because of distinct function in both query.so i am using distinct in outer query.Now performance is improved, but will it give same output?Both query are same in logic?
select distinct a,b,c,d from (
select a,b,c,d from html_details
union all
select a,b,c,d from pdf_details
)a
sql-server-2012 distinct-values
asked Dec 29 '18 at 16:04
RamRam
1578
add a comment |
I have below tables.
create table html_details(A int,b int,c int,d nvarchar(4))
create table pdf_details(A int,b int,c int,d nvarchar(4))
insert into pdf_details values(1,2,3,'pdf')
insert into pdf_details values(1,2,3,'pdf')
insert into pdf_details values(4,5,6,'pdf')
insert into html_details values(1,2,3,'html')
insert into html_details values(1,2,3,'html')
insert into html_details values(4,5,6,'html')
now i am using below query to avoid duplication in each tables.
select distinct a,b,c,d from html_details
union all
select distinct a,b,c,d from pdf_details
but above query gives poor performance because of distinct function in both query.so i am using distinct in outer query.Now performance is improved, but will it give same output?Both query are same in logic?
select distinct a,b,c,d from (
select a,b,c,d from html_details
union all
select a,b,c,d from pdf_details
)a
sql-server-2012 distinct-values
asked Dec 29 '18 at 16:04
RamRam
1578
I have below tables.
create table html_details(A int,b int,c int,d nvarchar(4))
create table pdf_details(A int,b int,c int,d nvarchar(4))
insert into pdf_details values(1,2,3,'pdf')
insert into pdf_details values(1,2,3,'pdf')
insert into pdf_details values(4,5,6,'pdf')
insert into html_details values(1,2,3,'html')
insert into html_details values(1,2,3,'html')
insert into html_details values(4,5,6,'html')
now i am using below query to avoid duplication in each tables.
select distinct a,b,c,d from html_details
union all
select distinct a,b,c,d from pdf_details
but above query gives poor performance because of distinct function in both query.so i am using distinct in outer query.Now performance is improved, but will it give same output?Both query are same in logic?
select distinct a,b,c,d from (
select a,b,c,d from html_details
union all
select a,b,c,d from pdf_details
)a
sql-server-2012 distinct-values
sql-server-2012 distinct-values
asked Dec 29 '18 at 16:04
RamRam
1578
asked Dec 29 '18 at 16:04
RamRam
1578
asked Dec 29 '18 at 16:04
RamRam
1578
asked Dec 29 '18 at 16:04
RamRam
1578
asked Dec 29 '18 at 16:04
RamRam
1578
1578
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
No. It will not return the same output.
Distinct in individual queries will get you unique records from both the queries and then it will be union-ed. So if there are similar rows in both the queries results, both of them will be present in final result.
Lets say your data is:
Table 1:
1,2,3,pdf
1,2,3,pdf
1,2,3,hello
Table 2:
1,2,3,html
1,2,3,html
1,2,3,hello
First approach's result will be (There's no distinct in final response) -
1,2,3,pdf
1,2,3,hello
1,2,3,html
1,2,3,hello
Second approach's result will be (There's a distinct in final response) -
1,2,3,pdf
1,2,3,html
1,2,3,hello
I hope this explains.
answered Dec 29 '18 at 16:17
Raman ShrivastavaRaman Shrivastava
2,6751023
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
No. It will not return the same output.
Distinct in individual queries will get you unique records from both the queries and then it will be union-ed. So if there are similar rows in both the queries results, both of them will be present in final result.
Lets say your data is:
Table 1:
1,2,3,pdf
1,2,3,pdf
1,2,3,hello
Table 2:
1,2,3,html
1,2,3,html
1,2,3,hello
First approach's result will be (There's no distinct in final response) -
1,2,3,pdf
1,2,3,hello
1,2,3,html
1,2,3,hello
Second approach's result will be (There's a distinct in final response) -
1,2,3,pdf
1,2,3,html
1,2,3,hello
I hope this explains.
answered Dec 29 '18 at 16:17
Raman ShrivastavaRaman Shrivastava
2,6751023
add a comment |
No. It will not return the same output.
Distinct in individual queries will get you unique records from both the queries and then it will be union-ed. So if there are similar rows in both the queries results, both of them will be present in final result.
Lets say your data is:
Table 1:
1,2,3,pdf
1,2,3,pdf
1,2,3,hello
Table 2:
1,2,3,html
1,2,3,html
1,2,3,hello
First approach's result will be (There's no distinct in final response) -
1,2,3,pdf
1,2,3,hello
1,2,3,html
1,2,3,hello
Second approach's result will be (There's a distinct in final response) -
1,2,3,pdf
1,2,3,html
1,2,3,hello
I hope this explains.
answered Dec 29 '18 at 16:17
Raman ShrivastavaRaman Shrivastava
2,6751023
add a comment |
No. It will not return the same output.
Distinct in individual queries will get you unique records from both the queries and then it will be union-ed. So if there are similar rows in both the queries results, both of them will be present in final result.
Lets say your data is:
Table 1:
1,2,3,pdf
1,2,3,pdf
1,2,3,hello
Table 2:
1,2,3,html
1,2,3,html
1,2,3,hello
First approach's result will be (There's no distinct in final response) -
1,2,3,pdf
1,2,3,hello
1,2,3,html
1,2,3,hello
Second approach's result will be (There's a distinct in final response) -
1,2,3,pdf
1,2,3,html
1,2,3,hello
I hope this explains.
answered Dec 29 '18 at 16:17
Raman ShrivastavaRaman Shrivastava
2,6751023
No. It will not return the same output.
Distinct in individual queries will get you unique records from both the queries and then it will be union-ed. So if there are similar rows in both the queries results, both of them will be present in final result.
Lets say your data is:
Table 1:
1,2,3,pdf
1,2,3,pdf
1,2,3,hello
Table 2:
1,2,3,html
1,2,3,html
1,2,3,hello
First approach's result will be (There's no distinct in final response) -
1,2,3,pdf
1,2,3,hello
1,2,3,html
1,2,3,hello
Second approach's result will be (There's a distinct in final response) -
1,2,3,pdf
1,2,3,html
1,2,3,hello
I hope this explains.
answered Dec 29 '18 at 16:17
Raman ShrivastavaRaman Shrivastava
2,6751023
answered Dec 29 '18 at 16:17
Raman ShrivastavaRaman Shrivastava
2,6751023
answered Dec 29 '18 at 16:17
Raman ShrivastavaRaman Shrivastava
2,6751023
answered Dec 29 '18 at 16:17
Raman ShrivastavaRaman Shrivastava
2,6751023
2,6751023
add a comment |
add a comment |
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