Join(two tables)

Basic sentence

SELECT columns
FROM table1
() JOIN table2
ON table1.column_name=table2.column_name; 

INNER JOIN

INNER JOIN equals to JOIN,

Explicit form

INNER JOIN

Implicit form

JOIN

Tables :

Person :

personID	lastName	firstName
1	Wang	Allen
2	Alice	Bob

Address:

addressID	personID	city	state
1	2	New York City	New York
2	3	Leetcode	California

SELECT Person.firstName, Address.city
FROM Person
INNER JOIN Address
ON Person.personID = Address.personID;

result:

firstName	city
Bob	New York City

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LEFT JOIN

Tables :

SELECT Person.firstName, Address.city
FROM Person LEFT JOIN Address # Write in one line is more intuitive
ON Person.personID = Address.personID;

result:

firstName	city
Bob	New York City
Allen	NULL

---

RIGHT JOIN

Tables :

SELECT Person.firstName, Address.city
FROM Person RIGHT JOIN Address # Write in one line is more intuitive
ON Person.personID = Address.personID;

result:

firstName	city
Bob	New York City
NULL	Leetcode

---

FULL JOIN

Tables :

SELECT Person.firstName, Address.city
FROM Person 
FULL JOIN Address
ON Person.personID = Address.personID;

result:

firstName	city
Bob	New York City
Allen	NULL
NULL	Leetcode

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Summary