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2. Projection (relational algebra) - Wikipedia

   en.wikipedia.org/.../Projection_(relational_algebra)

   In practical terms, if a relation is thought of as a table, then projection can be thought of as picking a subset of its columns. For example, if the attributes are (name, age), then projection of the relation {(Alice, 5), (Bob, 8)} onto attribute list (age) yields {5,8} – we have discarded the names, and only know what ages are present.

3. Selection (relational algebra) - Wikipedia

   en.wikipedia.org/wiki/Selection_(relational_algebra)

   Mutation and Selection. In relational algebra, a selection (sometimes called a restriction in reference to E.F. Codd's 1970 paper [1] and not, contrary to a popular belief, to avoid confusion with SQL's use of SELECT, since Codd's article predates the existence of SQL) is a unary operation that denotes a subset of a relation.

4. Relational algebra - Wikipedia

   en.wikipedia.org/wiki/Relational_algebra

   The relational algebra uses set union, set difference, and Cartesian product from set theory, and adds additional constraints to these operators to create new ones.. For set union and set difference, the two relations involved must be union-compatible—that is, the two relations must have the same set of attributes.

5. Projection (mathematics) - Wikipedia

   en.wikipedia.org/wiki/Projection_(mathematics)

   For example, the mapping that takes a point (x, y, z) in three dimensions to the point (x, y, 0) is a projection. This type of projection naturally generalizes to any number of dimensions n for the domain and k ≤ n for the codomain of the mapping. See Orthogonal projection, Projection (linear algebra). In the case of orthogonal projections ...

6. Projection (set theory) - Wikipedia

   en.wikipedia.org/wiki/Projection_(set_theory)

   Projection (measure theory) Projection (linear algebra) – Idempotent linear transformation from a vector space to itself; Projection (relational algebra) – Operation that restricts a relation to a specified set of attributes; Relation (mathematics) – Relationship between two sets, defined by a set of ordered pairs

7. Postal Service worker accused of swiping cash, coins and ...

   www.aol.com/news/postal-worker-accused-swiping...

   A U.S. Postal Service worker from Compton was arrested on suspicion of swiping more than 20 checks from the mail and depositing $281,000 into various bank accounts under her name, authorities said.