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Data Integration (Joins Example walkthrough (orders table (belong to…
Data Integration
Joins Example walkthrough
customers table
orders table
belong to customers in customer table
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use inner join to combine tables
use inner join to combine w employee table
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use inner join to combine with Sales table
add product names, use inner join to combine w products table
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employee table
order details table (Sales)
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products table
Joins
Outer Join
Full outer join
inner join + left outer join + right outer join
Right outer join
same as inner join plus:
adds rows from right table w no corresponding values in left table
Left outer join
same as inner join plus:
adds rows from left table w/o corresponding rows in right table too
will contain NULLS
Inner Join
each row in left table is:
combined horizontally w any row in right table w same identity value
can be used with carefully curated databases
best way to learn is to practice
Unions
useful for:
dataets that contain unique sets of cases sharing the same or very similar columns
ex: colleges w multiple databases about individual student activity
need to combine all info about student to integrate data
hard for companies to find duplicate records to use union
some cases where unions are always right answer, not joins