Introduction to Joins In Tableau

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Join is a query that combines the data from 2 or more tables, sheets, files in a single datasource based on the join condition

Rules to perform Join:
To perform Join we are having two rules
1) Both the tables should have a common column
2) Based on the common data type in the both tables

Join Types:
Depending on the join condition. Joins are divided into two types 
1) Equi Joins
2) Non-Equi Joins
Equi Joins: In the Join condition if you use the equality operator (“=”) then such a kind of Join is called as “ Equi Join”
Non-Equi Joins: In the Join condition apart from the equality if we use any operator like <,>,<>,<=,>= etc.
Suck kind of join is known as “Non-equi Join”
Equi Join Types:
Equi Join is divided into 3 types
1. Inner Join
2. Outer Join
3. Self Join
Again outer join is divided into 3 different types
1. Left Outer
2. Right Outer
3. Full Outer
Inner Join: 
Inner Join combines the data from two tables and it display only the matching records (or) common records.

Join Condition: Table1.ID=Table2.ID

Table 1:

Name	ID
Ramesh	1
Ravi	2
Praveen	3
Kiran	4

Table 2:

ID	Designtion
1	Professor
2	Professor
3	Professor
4	Principal

Output:

Name	Designation
Ramesh	Professor
Ravi	Professor
Praveen	Professor

Outer Join
Left Outer Join: 
Is is display the complete data from the left table and matching records from the the Right Table.

Table1.ID=Table2.ID(+)

Following Above Table 1 & Table 2

Output:

Name	Designation
Ravi	Professor
Ramesh	Professor
Praveen	Professor
Kiran	Null

Right Outer Join: 
It is display complete data from right table and matching records from left table.

Table1.ID(+)=Table2.ID

Following Above Table 1 & Table 2

Output:

Name	Designation
Ramesh	Professor
Ravi	Professor
Praveen	Profess
Null	Principal

Full Outer Join: 
It displays the complete data from both the tables

Following Above Table 1 & Table 2

Output:

Name	Designation
Ramesh	Professor
Ravi	Professor
Praveen	Professor
Kiran	Null
Null	Principla

Self Join: 
Performing a join to the same table itself is known as “Self Join”