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An inner join (or join) requires each row in the two joined tables to have matching column values, and is a commonly used join operation in applications but should not be assumed to be the best choice in all situations. Inner join creates a new result table by combining column values of two tables (A and B) based upon the join-predicate.
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.
The recursive join is an operation used in relational databases, also sometimes called a "fixed-point join". It is a compound operation that involves repeating the join operation, typically accumulating more records each time, until a repetition makes no change to the results (as compared to the results of the previous iteration).
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Also one of the SQL standard SQL-89 and SQL-92 authors Joe Celko said "Frankly, NATURAL JOIN was a bad idea. Any change to a table can suddenly add or remove a column in the join on the fly. Any change to a table can suddenly add or remove a column in the join on the fly.
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A foreign key is a set of attributes in a table that refers to the primary key of another table, linking these two tables. In the context of relational databases, a foreign key is subject to an inclusion dependency constraint that the tuples consisting of the foreign key attributes in one relation, R, must also exist in some other (not necessarily distinct) relation, S; furthermore that those ...
Join: The function Join is on two red–black trees t 1 and t 2 and a key k, where t 1 < k < t 2, i.e. all keys in t 1 are less than k, and all keys in t 2 are greater than k. It returns a tree containing all elements in t 1, t 2 also as k. If the two trees have the same black height, Join simply creates a new node with left subtree t 1, root k ...