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Chapter 9 (Joining spreadsheets (More relevant columns are added as…
Chapter 9
Joining spreadsheets
More relevant columns are added as datasets are merged
Three kinds
Outer join
Left outer
Full outer
Right outer
Inner join
The inner join produces a header row and
two data rows (here shown in CSV format,
spaces after commas for readability):
CustId, Name, CustId, Product
1, Kai, 1, pants
1, Kai, 1, bouncing castle
The left outer join produces a header row
and three data rows:
CustId, Name, CustId, Product
1, Kai, 1, pants
1, Kai, 1, bouncing castle
2, Dan, NULL, NULL
The NULLs here indicate that Dan bought
nothing yet.
The right outer join produces a header row
and three data rows:
CustId, Name, CustId, Product
1,Kai,1, pants
1,Kai,1, bouncing castle
NULL, NULL, 3, sunglasses
The NULLs here indicate that we do not
know who bought the glasses
The full outer join produces a header row
and four data rows:
CustId, Name, CustId, Product
1,Kai,1, pants
1,Kai,1, bouncing castle
2, Dan, NULL, NULL
NULL, NULL, 3, sunglasses
Now we get all information from both
tables combined.
Unionizing data tables
This is when more rows are added in
EX: Compiling a list of churches and then seeing if there is a "customer" overlap
Appendix F
Boolean expression
A!=B
A >= B
A IN B
A OR B
A OR (B AND C)
A will trigger or if simultaneously B and C are true
A or B. Cough
A in the set B
A is greater than or equal to B
A is not equal to B
App. G, but still helpful
This promotes referential integrity as the customers must be on the list
