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  2. Unique key - Wikipedia

    en.wikipedia.org/wiki/Unique_key

    In SQL, the unique keys have a UNIQUE constraint assigned to them in order to prevent duplicates (a duplicate entry is not valid in a unique column). Alternate keys may be used like the primary key when doing a single-table select or when filtering in a where clause, but are not typically used to join multiple tables.

  3. Object copying - Wikipedia

    en.wikipedia.org/wiki/Object_copying

    One method of copying an object is the shallow copy.In that case a new object B is created, and the fields values of A are copied over to B. [3] [4] [5] This is also known as a field-by-field copy, [6] [7] [8] field-for-field copy, or field copy. [9]

  4. Comparison of relational database management systems - Wikipedia

    en.wikipedia.org/wiki/Comparison_of_relational...

    8,060 bytes / 2 TB 6: 1,024 / 30,000(with sparse columns) 2 GB / Unlimited (using RBS/FILESTREAM object) 2 GB 6: 126 bits 2: 0001 9999 128 Microsoft SQL Server Compact (Embedded Database) 4 GB 4 GB 8,060 bytes 1024 2 GB 4000 154 bits 0001 9999 128 Mimer SQL: Unlimited Unlimited 16000 (+lob data) 252 Unlimited 15000 45 digits 0001-01-01 9999-12 ...

  5. Column (database) - Wikipedia

    en.wikipedia.org/wiki/Column_(database)

    A column may contain text values, numbers, or even pointers to files in the operating system. [2] Columns typically contain simple types, though some relational database systems allow columns to contain more complex data types, such as whole documents, images, or even video clips. [3] [better source needed] A column can also be called an attribute.

  6. Duplicate code - Wikipedia

    en.wikipedia.org/wiki/Duplicate_code

    In computer programming, duplicate code is a sequence of source code that occurs more than once, either within a program or across different programs owned or maintained by the same entity. Duplicate code is generally considered undesirable for a number of reasons. [ 1 ]

  7. Rule of three (computer programming) - Wikipedia

    en.wikipedia.org/wiki/Rule_of_three_(computer...

    It states that two instances of similar code do not require refactoring, but when similar code is used three times, it should be extracted into a new procedure. The rule was popularised by Martin Fowler in Refactoring [1] and attributed to Don Roberts. Duplication is considered a bad practice in programming because it makes the code harder to ...

  8. Swap (computer programming) - Wikipedia

    en.wikipedia.org/wiki/Swap_(computer_programming)

    In computer programming, the act of swapping two variables refers to mutually exchanging the values of the variables. Usually, this is done with the data in memory. For example, in a program, two variables may be defined thus (in pseudocode): data_item x := 1 data_item y := 0 swap (x, y);

  9. Comparative research - Wikipedia

    en.wikipedia.org/wiki/Comparative_research

    Comparative research, simply put, is the act of comparing two or more things with a view to discovering something about one or all of the things being compared. This technique often utilizes multiple disciplines in one study. When it comes to method, the majority agreement is that there is no methodology peculiar to comparative research. [1]