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Set operations in SQL is a type of operations which allow the results of multiple queries to be combined into a single result set. [1] Set operators in SQL include UNION, INTERSECT, and EXCEPT, which mathematically correspond to the concepts of union, intersection and set difference.
In very early versions of the SQL standard the return code was called SQLCODE and used a different coding schema. The following table lists the standard-conforming values - based on SQL:2011. [1] The table's last column shows the part of the standard that defines the row. If it is empty, the definition originates from part 2 Foundation.
The nested set model is a technique for representing nested set collections (also known as trees or hierarchies) in relational databases.. It is based on Nested Intervals, that "are immune to hierarchy reorganization problem, and allow answering ancestor path hierarchical queries algorithmically — without accessing the stored hierarchy relation".
In standard SQL:1999 hierarchical queries are implemented by way of recursive common table expressions (CTEs). Unlike Oracle's earlier connect-by clause, recursive CTEs were designed with fixpoint semantics from the beginning. [1] Recursive CTEs from the standard were relatively close to the existing implementation in IBM DB2 version 2. [1]
Some authors [1] do not assume that B is nonempty. The second condition states that the intersection of every couple of sets in the nested set collection is not the empty set only if one set is a subset of the other. [2] In particular, when scanning all pairs of subsets at the second condition, it is true for any combination with B.
SQL-92 was the third revision of the SQL database query language. Unlike SQL-89, it was a major revision of the standard. Aside from a few minor incompatibilities, the SQL-89 standard is forward-compatible with SQL-92. The standard specification itself grew about five times compared to SQL-89.
Many authors also use concatenation of a string set and a single string, and vice versa, which are defined similarly by S 1 w = { vw : v ∈ S 1} and vS 2 = { vw : w ∈ S 2}. In these definitions, the string vw is the ordinary concatenation of strings v and w as defined in the introductory section.
[2] AQL is a query language for the ArangoDB native multi-model database system..QL is a proprietary object-oriented query language for querying relational databases; successor of Datalog; CodeQL is the analysis engine used by developers to automate security checks, and by security researchers to perform variant analysis on GitHub.