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Oracle Corporation calls these variables "substitution variables". Programmers can use them anywhere in a SQL or PL/SQL statement or in SQL Plus commands. They can be populated by a literal using DEFINE or from the database using the column command. predefined variables, prefixed with an underscore ('_') [10]
It allows the declaration of constants and variables, procedures, functions, packages, types and variables of those types, and triggers. Arrays are supported involving the use of PL/SQL collections. Implementations from version 8 of Oracle Database onwards have included features associated with object-orientation. One can create PL/SQL units ...
Oracle implemented a special variable type for APEX called Substitution Variables (with a syntax of "&NAME."); however, these are insecure and can lead to SQL injections. When an injection occurs within a PL/SQL block, an attacker can inject an arbitrary number of queries or statements to execute.
Microsoft Access: A table named DUAL may be created and the single-row constraint enforced via ADO (Table-less UNION query in MS Access) Microsoft SQL Server: SQL Server does not require a dummy table. Queries like 'select 1 + 1' can be run without a "from" clause/table name. [5] MySQL allows DUAL to be specified as a table in queries that do ...
Queries can be nested so that the results of one query can be used in another query via a relational operator or aggregation function. A nested query is also known as a subquery. While joins and other table operations provide computationally superior (i.e. faster) alternatives in many cases, the use of subqueries introduces a hierarchy in ...
Major DBMSs, including SQLite, [5] MySQL, [6] Oracle, [7] IBM Db2, [8] Microsoft SQL Server [9] and PostgreSQL [10] support prepared statements. Prepared statements are normally executed through a non-SQL binary protocol for efficiency and protection from SQL injection, but with some DBMSs such as MySQL prepared statements are also available using a SQL syntax for debugging purposes.
Queries can be nested so that the results of one query can be used in another query via a relational operator or aggregation function. A nested query is also known as a subquery. While joins and other table operations provide computationally superior (i.e. faster) alternatives in many cases (all depending on implementation), the use of ...
There are two main types of variable-expanding algorithms for variable interpolation: [3] Replace and expand placeholders: creating a new string from the original one, by find–replace operations. Find variable reference (placeholder), replace it by its variable value. This algorithm offers no cache strategy.