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Chapter 9: Data Integration (Join (Two Types of Joins (Outer Join (Left…
Chapter 9: Data Integration
Join
Two Types of Joins
Inner Join
Each row in left table is combined horizontally with any row in a right table that has same identity value
When dealing with carefully curated databases, we will use inner join
Outer Join
Right outer join
Same result as an inner join, but includes and rows from the right table that do not have any corresponding in the left
Full outer join
Join produces the same result as an inner join + left outer join + right outer join
Left outer join
Same as inner join, but adds any rows from the left table that do not have any corresponding rows in the right
Used if we are just trying to collect consumer data
Combines two datasets with a shared identity value
Based on relational algebra, thus best way to know them is to practice
Unions
Allows the ability to combine two datasets
We perform unions when we have datasets that contain unique sets of cases sharing the same or similar columns
Imputation
The replacing of missing data in a column with the assignment of reasonable values
Exercises
Difference between an inner and outer join
Outer joins add rows that may not have corresponding rows with another table. Inner joins only do same exact identity value
Whats the relationship between joins and unions
Joins combine tables whereas unions combine data sets. They are both similar because they combine data, just in different ways.
Steven Chesney
Email:
stch1109@colorado.edu
Class: 3201-002
Prof: Larsen