2. Disclaimer: This presentation is prepared by trainees of
baabtra as a part of mentoring program. This is not official
document of baabtra –Mentoring Partner
Baabtra-Mentoring Partner is the mentoring division of baabte System Technologies Pvt .
Ltd
3. Union and Intersection
Zabeeb anwar
zabeebanwar@gmail.com
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8. Union
- A hot startup is holding a special event and
wants to send out invites for my marriage()
to some of my best clients and also to some
VIPs.
- Some of the VIPs are actually very supportive
of the site and are clients too.
- What query will provide the complete set of
people to invite avoiding duplicate records?
- Here is our data.
9. Union
• create database hotstartup;
• create table clients(name varchar);
insert into clients values(‘Sharan');
insert into clients values(‘Vineesh');
insert into clients values(‘Bala');
insert into clients values(‘Sheethal');
• create table vips(name varchar);
insert into vips values(‘Reshmi');
insert into vips values(‘Sheethal');
insert into vips values(‘Anupa');
insert into vips values(‘Ashwathy');
10. Union
• hotstartup=# select * from clients union select *
from vips;
name
----------------
Sharan
Vineesh
Bala
Sheethal
Reshmi
Anupa
Ashwathy
(7 rows)
11. Union All
• hotstartup=# select * from clients union all select * from vips;
name
----------------
Sharan
Vineesh
Bala
Sheethal
Reshmi
sheethal
Anupa
Ashwathy
(8 rows)
12. Intersect
• if I want to get the list of people who are both
clients and VIP we can use INTERSECT.
• hotstartup=# select * from
clients intersect select * from vips;
name
----------------
Sheethal
(1 row)
13. Intersect All
• Let's insert a Sheethal(duplicate name) into VIP’s.
name
----------------
Sharan
Vineesh
Bala
Sheethal
Sheethal
(4 rows)
-select * from client intersect all select * from vips;
15. Except
• I want everyone on the clients list EXCEPT those on
the VIP list.
• select * from clients except select * from vips;
name
----------------
Sharan
Vineesh
Bala
16. Except All
• Let's insert a Sheethal(duplicate name) into clients.
name
----------------
Sharan
Vineesh
Bala
Sheethal
Sheethal
(4 rows)
-select * from clients except all select * from vips;
18. Where Clause
• select * from Clients_Year;
name | Birth year
------------------+------
Sharan | 1976
Vineesh | 1977
Bala | 1978
Ashwathy | 1983
Reshmi | 199 3
sheethal | 1996
Anupa | 1997
19. Where Clause
• select * from clients_year where year
between 1970 and 1979 union select * from
ceos where year=1977;
name | Birth year
------------------+------
Sharan | 1976
Vineesh | 1977
Bala | 1978
20. Do not
• select * from clients where year between
1970 and 1979 union select name from clients
where year=1977;
ERROR: each UNION query must have the
same number of columns
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