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There is also an IGNORE clause for the INSERT statement, [7] which tells the server to ignore "duplicate key" errors and go on (existing rows will not be inserted or updated, but all new rows will be inserted). SQLite's INSERT OR REPLACE INTO works similarly. It also supports REPLACE INTO as an alias for compatibility with MySQL. [8]
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.
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 ]
"Don't repeat yourself" (DRY), also known as "duplication is evil", is a principle of software development aimed at reducing repetition of information which is likely to change, replacing it with abstractions that are less likely to change, or using data normalization which avoids redundancy in the first place.
For example, removing duplicates using distinct may be slow in the database; thus, it makes sense to do it outside. On the other side, if using distinct significantly (x100) decreases the number of rows to be extracted, then it makes sense to remove duplications as early as possible in the database before unloading data.
The individual entries have a copy-on-write behavior that is non-aliasing, i.e. changing one copy afterwards will not affect other copies. [9] Microsoft's ReFS also supports this operation. [10] Target deduplication is the process of removing duplicates when the data was not generated at that location.
Duplicate images – tool to show duplicate files between Wikipedia and Commons (at the toolserver) Push-for-commons – tool to show a set of images from a wikipedia, helping to find license problems, {{ NowCommons }} candidates, and images that should be copied/moved to the commons (at the toolserver)
Quite a few languages make the encoding part of the string object, and thus store and support a large set of encodings including UTF-16. Most consider UTF-16 and UCS-2 to be different encodings. Examples are the PHP language [37] and MySQL. [38]