What is the difference between projection and selection? Is it:
- Projection --> for selecting the columns of table; and
- Selection ---> to select the rows of table?
So are projection and selection vertical and horizontal slicing respectively?
What are projection and selection?
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4 Answers
Exactly.
Projection means choosing which columns (or expressions) the query shall return.
Selection means which rows are to be returned.
if the query is
select a, b, c from foobar where x=3;
then "a, b, c" is the projection part, "where x=3" the selection part.
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