# SQLite/Introduction
## Design

Unlike client–server database management systems, the SQLite engine has no standalone processes with which the application program communicates. Instead, the SQLite library is linked in and thus becomes an integral part of the application program. The library can also be called dynamically. The application program uses SQLite's functionality through simple function calls, which reduce latency in database access: function calls within a single process are more efficient than inter-process communication. SQLite stores the entire database (definitions, tables, indices, and the data itself) as a single cross-platform file on a host machine. It implements this simple design by locking the entire database file during writing. SQLite read operations can be multitasked, though writes can only be performed sequentially.
Due to the server-less design, SQLite applications require less configuration than client-server databases. SQLite is called zero-conf because it does not require service management (such as startup scripts) or access control based on GRANT and passwords. Access control is handled by means of file system permissions given to the database file itself. Databases in client-server systems use file system permissions which give access to the database files only to the daemon process.
Another implication of the serverless design is that several processes may not be able to write to the database file. In server-based databases, several writers will all connect to the same daemon, which is able to handle its locks internally. SQLite on the other hand has to rely on file-system locks. It has less knowledge of the other processes that are accessing the database at the same time. Therefore, SQLite is not the preferred choice for write-intensive deployments. However, for simple queries with little concurrency, SQLite performance profits from avoiding the overhead of passing its data to another process.
SQLite uses PostgreSQL as a reference platform. “What would PostgreSQL do” is used to make sense of the SQL standard. One major deviation is that, with the exception of primary keys, SQLite does not enforce type checking; the type of a value is dynamic and not strictly constrained by the schema (although the schema will trigger a conversion when storing, if such a conversion is potentially reversible). SQLite strives to follow Postel's Rule.

## History

D. Richard Hipp designed SQLite in the spring of 2000 while working for General Dynamics on contract with the United States Navy. Hipp was designing software used aboard guided missile destroyers, which originally used HP-UX with an IBM Informix database back-end. SQLite began as a Tcl extension.
The design goals of SQLite were to allow the program to be operated without installing a database management system or requiring a database administrator. Hipp based the syntax and semantics on those of PostgreSQL 6.5. In August 2000, version 1.0 of SQLite was released, with storage based on gdbm (GNU Database Manager). SQLite 2.0 replaced gdbm with a custom B-tree implementation, adding transaction capability. SQLite 3.0, partially funded by America Online, added internationalization, manifest typing, and other major improvements.
In 2011 Hipp announced his plans to add a NoSQL interface (managing documents expressed in JSON) to SQLite databases and to develop UnQLite, an embeddable document-oriented database.. UnQLite was released as an independent database.

## Features

SQLite implements most of the SQL-92 standard for SQL but it lacks some features. For example, it partially provides triggers, and it cannot write to views (however it provides INSTEAD OF triggers that provide this functionality). While it provides complex queries, it still has limited ALTER TABLE function, as it cannot modify or delete columns.
SQLite uses an unusual type system for an SQL-compatible DBMS; instead of assigning a type to a column as in most SQL database systems, types are assigned to individual values; in language terms it is dynamically typed. Moreover, it is weakly typed in some of the same ways that Perl is: one can insert a string into an integer column (although SQLite will try to convert the string to an integer first, if the column's preferred type is integer). This adds flexibility to columns, especially when bound to a dynamically typed scripting language. However, the technique is not portable to other SQL products. A common criticism is that SQLite's type system lacks the data integrity mechanism provided by statically typed columns in other products. The SQLite web site describes a "strict affinity" mode, but this feature has not yet been added. However, it can be implemented with constraints like CHECK(typeof(x)='integer').
SQLite with full Unicode function is optional.
Several computer processes or threads may access the same database concurrently. Several read accesses can be satisfied in parallel. A write access can only be satisfied if no other accesses are currently being serviced. Otherwise, the write access fails with an error code (or can automatically be retried until a configurable timeout expires). This concurrent access situation would change when dealing with temporary tables. This restriction is relaxed in version 3.7 when write-ahead logging (WAL) is turned on enabling concurrent reads and writes.
SQLite version 3.7.4 first saw the addition of the FTS4 (full text search) module, which features enhancements over the older FTS3 module. FTS4 allows users to perform full text searches on documents similar to how search engines search webpages. Version 3.8.2 added support for creating tables without rowid, which may provide space and performance improvements. Common table expressions support was added to SQLite in version 3.8.3.
In 2015, with the json1 extension and new subtype interfaces, SQLite version 3.9 introduced JSON content managing.

## Development and distribution

SQLite's code is hosted with Fossil, a distributed version control system that is itself built upon an SQLite database.
A standalone command-line program is provided in SQLite's distribution. It can be used to create a database, define tables, insert and change rows, run queries and manage an SQLite database file. It also serves as an example for writing applications that use the SQLite library.
SQLite uses automated regression testing prior to each release. Over 2 million tests are run as part of a release's verification. Starting with the August 10, 2009 release of SQLite 3.6.17, SQLite releases have 100% branch test coverage, one of the components of code coverage. The tests and test harnesses are partially public domain and partially proprietary.

## Notable users

* The browsers Google Chrome, Opera, Safari and the Android Browser all allow for storing information in, and retrieving it from, a SQLite database within the browser, using the Web SQL Database technology, although this is rapidly becoming deprecated (namely superseded by IndexedDB).
* Mozilla Firefox and Mozilla Thunderbird store a variety of configuration data (bookmarks, cookies, contacts etc.) in internally managed SQLite databases. There is a third-party add-on that uses the code supporting this functionality to provide a user interface for managing arbitrary SQLite databases.
* Various web application frameworks
* Adobe Systems uses SQLite as its file format in Adobe Photoshop Lightroom, a standard database in Adobe AIR, and internally within Adobe Reader.
* Evernote uses SQLite to store its local database repository in Windows.
* Skype
* Apple adopted it as an option in macOS's Core Data API from the original implementation in Mac OS X 10.4 onwards, and also for administration of videos and songs, and in iOS for storage of text messages on the iPhone.
* Windows 10

## Programming language support

A large number of programming languages provide bindings for SQLite, including:
* AutoIt
* various dialects of BASIC including FreeBASIC, PureBasic, RFO BASIC!, Visual Basic and Xojo
* C
* C#
* C++
* Clipper//Harbour
* Curl
* D
* Elixir
* Emacs Lisp
* F#
* Go
* Haskell
* Haxe
* Java (on JVM and DVM)
* JavaScript
* Julia
* distributions of Lisp such as Common Lisp, newLisp, OpenLisp
* Transcript (on LiveCode)
* LabVIEW
* Lua
* MATLAB
* Nim
* Objective-C (on macOS and iOS)
* OCaml
* several flavours of Pascal including Free Pascal, Component Pascal and Delphi
* Perl
* PHP
* Pike
* Python
* R
* Racket
* REBOL
* Ruby
* Scheme
* Smalltalk
* Swift (on macOS and iOS)
* Tcl
* Xojo

## References
### Citations

* ↑ "SQLite Is A Zero-Configuration Database". SQLite.org. Retrieved August 3, 2015.
* ↑ "Appropriate Uses For SQLite". SQLite.org. Retrieved 2015-09-03.
* ↑ "PGCon 2014: Clustering and VODKA". Lwn.net. Retrieved 2017-01-06.
* ↑ "PGCon2014: SQLite: Protégé of PostgreSQL". Pgcon.org. Retrieved 2017-01-06.
* 1 2 "SQLite: StrictMode". Sqlite.org. Retrieved September 3, 2015.
* 1 2 Owens, Michael (2006). The Definitive Guide to SQLite. Apress. doi:10.1007/978-1-4302-0172-4_1. ISBN 978-1-59059-673-9.
* 1 2 "Well-Known Users Of SQLite". SQLite. Retrieved August 5, 2015.
* ↑ "Interview: Richard Hipp on UnQL, a New Query Language for Document Databases". InfoQ. August 4, 2011. Retrieved October 5, 2011.
* ↑ UnQLite FAQ
* ↑ "SQL Features That SQLite Does Not Implement". SQLite.org. January 1, 2009. Retrieved October 14, 2009.
* ↑ "Case-insensitive matching of Unicode characters does not work". SQLite Frequently Asked Questions. Retrieved 2015-09-03.
* ↑ "Write Ahead Logging in SQLite 3.7". SQLite.org. Retrieved September 3, 2011. WAL provides more concurrency as readers do not block writers and a writer does not block readers. Reading and writing can proceed concurrently
* ↑ "SQLite Release 3.7.4 On 2010-12-08". SQLite.org. December 8, 2010. Retrieved September 3, 2015.
* ↑ "SQLite FTS3 and FTS4 Extensions". SQLite.org. Retrieved September 3, 2015.
* ↑ "SQLite Release 3.8.2 On 2013-12-06". SQLite.org. December 6, 2013. Retrieved September 3, 2015.
* ↑ "The WITHOUT ROWID Optimization". SQLite.org. Retrieved September 3, 2015.
* ↑ "SQLite Release 3.8.3 On 2014-02-03". SQLite.org. February 3, 2014. Retrieved September 3, 2015.
* ↑ https://sqlite.org/json1.html
* ↑ "Fossil: Fossil Performance". Fossil-scm.org. August 23, 2009. Retrieved September 12, 2009.
* ↑ "How SQLite Is Tested". SQLite.org. Retrieved September 12, 2009.
* ↑ "SQLite Manager :: Add-ons for Firefox". Addons.mozilla.org. 2015-02-28. Retrieved 2017-01-06.
* ↑ "Skype client using SQLite?". Mail-archive.com. August 28, 2007. Retrieved June 14, 2010.
* ↑ "Show Download History List of All Files Ever Downloaded Within Mac OS X". Osxdaily.com. 2012-07-12. Retrieved 2017-01-06.
* ↑ "SQLite databases". Msdn.microsoft.com. 2016-09-19. Retrieved 2017-01-06.
* ↑ "User Defined Functions". Autoitscript.com. Retrieved 2017-01-06.
* ↑ "SQLite3 API for GNU Emacs 25+". github.com. Retrieved 2017-10-02.
* ↑ Ross McKinlay; Colin Bull. "SQLProvider". Fsprojects.github.io. Retrieved 2017-01-06.
* ↑ "Google Code Archive - Long-term storage for Google Code Project Hosting". Code.google.com. Retrieved 2017-01-06.
* ↑ Adam Kennedy. "DBD::SQLite - Self-contained RDBMS in a DBI Driver". Metacpan.org. Retrieved 2017-01-06.
* ↑ "PySqlite – The Trac Project". Trac.edgewall.org. 2015-12-31. Retrieved 2017-01-06.
* ↑ "Continue: Web Applications in Racket - 15 Using an SQL database". docs.racket-lang.org. Retrieved 2017-02-24.
* ↑ "Archived copy". Archived from the original on 2010-04-17. Retrieved 2010-04-03. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)CS1 maint: archived copy as title (link)

### Sources

* Allen, Grant; Owens, Mike (November 5, 2010). The Definitive Guide to SQLite (2nd ed.). Apress. p. 368. ISBN 1-4302-3225-0.
* Kreibich, Jay A. (August 17, 2010). Using SQLite (1st ed.). O'Reilly Media. p. 528. ISBN 0-596-52118-9.
* van der Lans, Rick F. (September 7, 2009). The SQL Guide to SQLite (1st ed.). lulu.com. p. 542. ISBN 0-557-07676-5.
* Newman, Chris (November 9, 2004). SQLite (Developer's Library) (1st ed.). Sams. p. 336. ISBN 0-672-32685-X.