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Union and intersection
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Disclaimer: This presentation is prepared by trainees of baabtra as a part of mentoring program. This is not official document of baabtra –Mentoring PartnerBaabtra-Mentoring Partner is the mentoring division of baabte System Technologies Pvt . Ltd
Union and Intersection
Zabeeb anwar [email protected] www.fb.com/zabeebanwar twitter.com/zabeebanwar
in/linkedin.com/in/zabeeb 9895599689
union
AUB- AUB(OR) means the union of sets A and B
contains all of the elements of both A and B.
Intersection
AÇB(AND) means the intersection of sets A and B. This contains all of the elements which are in both A and B.
Union and Intersection with empty
Union and Intersection in Psql
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.
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');
Union• hotstartup=# select * from clients union select *
from vips; name
---------------- Sharan Vineesh Bala Sheethal
Reshmi Anupa Ashwathy(7 rows)
Union All• hotstartup=# select * from clients union all select * from vips;
name ----------------SharanVineeshBalaSheethal
Reshmi sheethal Anupa
Ashwathy (8 rows)
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)
Intersect All• Let's insert a Sheethal(duplicate name) into VIP’s. name
----------------SharanVineeshBalaSheethal
Sheethal (4 rows)
-select * from client intersect all select * from vips;
Intersect All
name ----------------
sheethal sheethal
(2 rows) - Sheethal appears in both tables twice so we
find two matching pairs for her and hence two rows appears in the results.
Except• I want everyone on the clients list EXCEPT those on
the VIP list.• select * from clients except select * from vips; name
----------------SharanVineeshBala
Except All• Let's insert a Sheethal(duplicate name) into clients. name
----------------SharanVineeshBalaSheethal
Sheethal (4 rows)-select * from clients except all select * from vips;
Except All
name ----------------
SharanVineeshBala
Sheethal (4 rows)
Where Clause
• select * from Clients_Year; name | Birth year ------------------+------ Sharan | 1976 Vineesh | 1977 Bala | 1978 Ashwathy | 1983 Reshmi | 199 3 sheethal | 1996 Anupa | 1997
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
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
Union and intersection in Python
Example
>>>engineers = Set(['John', 'Jane', 'Jack', 'Janice'])
>>>programmers = Set(['Jack', 'Sam', 'Susan', 'Janice'])
>>>managers = Set(['Jane', 'Jack', 'Susan',
'Zack'])
Union
>>>employees = engineers | programmers | managers
>>>print “employees”Set(['Jane', 'Janice', 'John’,
'Jack’,’susan’,’Zack’,’sam’])
Intersection
>>>engineers = Set(['John', 'Jane', 'Jack', 'Janice'])
>>>managers = Set(['Jane', 'Jack', 'Susan', 'Zack'])
>>>engineering_management = engineers & managers
>>>print “engineering_management”Set(['Jane', 'Jack’])
Questions
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