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Query by Example (QBE) is a database query language for relational databases. It was devised by Moshé M. Zloof at IBM Research during the mid-1970s, in parallel to the development of SQL . [ 1 ] It is the first graphical query language, using visual tables where the user would enter commands, example elements and conditions.
Many trim functions have an optional parameter to specify a list of characters to trim, instead of the default whitespace characters. For example, PHP and Python allow this optional parameter, while Pascal and Java do not. With Common Lisp's string-trim function, the parameter (called character-bag) is required. The C++ Boost library defines ...
SQL syntax can be checked at compile time. The returned query results can also be checked strictly. Preprocessor might generate static SQL which performs better than dynamic SQL because query plan is created on program compile time, stored in database and reused at runtime. Static SQL can guarantee access plan stability.
Title Authors ----- ----- SQL Examples and Guide 4 The Joy of SQL 1 An Introduction to SQL 2 Pitfalls of SQL 1 Under the precondition that isbn is the only common column name of the two tables and that a column named title only exists in the Book table, one could re-write the query above in the following form:
String interpolation, like string concatenation, may lead to security problems. If user input data is improperly escaped or filtered, the system will be exposed to SQL injection, script injection, XML external entity (XXE) injection, and cross-site scripting (XSS) attacks. [4] An SQL injection example: query = "SELECT x, y, z FROM Table WHERE ...
In SQL, the data manipulation language comprises the SQL-data change statements, [3] which modify stored data but not the schema or database objects. Manipulation of persistent database objects, e.g., tables or stored procedures, via the SQL schema statements, [3] rather than the data stored within them, is considered to be part of a separate data definition language (DDL).
The query evaluation, and thus query containment, is LOGCFL-complete and thus in polynomial time. [9] Acyclicity of conjunctive queries is a structural property of queries that is defined with respect to the query's hypergraph : [ 6 ] a conjunctive query is acyclic if and only if it has hypertree-width 1.
The purpose of a PL/SQL function is generally used to compute and return a single value. This returned value may be a single scalar value (such as a number, date or character string) or a single collection (such as a nested table or array). User-defined functions supplement the built-in functions provided by Oracle Corporation. [6]