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The syntax of the SQL programming language is defined and maintained by ISO/IEC SC 32 as part of ISO/IEC 9075.This standard is not freely available. Despite the existence of the standard, SQL code is not completely portable among different database systems without adjustments.
Conjunctive queries without distinguished variables are called boolean conjunctive queries.Conjunctive queries where all variables are distinguished (and no variables are bound) are called equi-join queries, [1] because they are the equivalent, in the relational calculus, of the equi-join queries in the relational algebra (when selecting all columns of the result).
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 ...
They are implemented as a group of macro constants in the C standard library in the iso646.h header. The tokens were created by Bjarne Stroustrup for the pre-standard C++ language [1] and were added to the C standard in a 1995 amendment to the C90 standard via library to avoid the breakage of existing code.
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.
In the context of information retrieval, QBE has a somewhat different meaning. The user can submit a document, or several documents, and ask for "similar" documents to be retrieved from a document database [see search by multiple examples [2]]. Similarity search is based comparing document vectors (see Vector Space Model).
It was completed as ISO standard ISO/IEC 9075-3:1995 Information technology—Database languages—SQL—Part 3: Call-Level Interface (SQL/CLI). In the fourth quarter of 1994, control over the standard was transferred to the X/Open Company, which significantly expanded and updated it. The X/Open CLI interface is a superset of the ISO SQL CLI.
creates two different and incompatible types. The SQL distinct types use name equivalence not structural equivalence like typedefs in C. It's still possible to perform compatible operations on (columns or data) of distinct types by using an explicit type CAST. Few SQL systems support these. IBM Db2 is one those supporting them. [6]