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PostgreSQL, MySQL and Oracle support natural joins; Microsoft T-SQL and IBM DB2 do not. The columns used in the join are implicit so the join code does not show which columns are expected, and a change in column names may change the results. In the SQL:2011 standard, natural joins are part of the optional F401, "Extended joined table", package.
SQL was initially developed at IBM by Donald D. Chamberlin and Raymond F. Boyce after learning about the relational model from Edgar F. Codd [12] in the early 1970s. [13] This version, initially called SEQUEL (Structured English Query Language), was designed to manipulate and retrieve data stored in IBM's original quasirelational database management system, System R, which a group at IBM San ...
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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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.
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.
The hash join is an example of a join algorithm and is used in the implementation of a relational database management system.All variants of hash join algorithms involve building hash tables from the tuples of one or both of the joined relations, and subsequently probing those tables so that only tuples with the same hash code need to be compared for equality in equijoins.
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 ...