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diff --git a/www/different.html b/www/different.html new file mode 100644 index 0000000..8f315ce --- /dev/null +++ b/www/different.html @@ -0,0 +1,358 @@ +<!DOCTYPE html> +<html><head> +<meta name="viewport" content="width=device-width, initial-scale=1.0"> +<meta http-equiv="content-type" content="text/html; charset=UTF-8"> +<link href="sqlite.css" rel="stylesheet"> +<title>Distinctive Features Of SQLite</title> +<!-- path= --> +</head> +<body> +<div class=nosearch> +<a href="index.html"> +<img class="logo" src="images/sqlite370_banner.gif" alt="SQLite" border="0"> +</a> +<div><!-- IE hack to prevent disappearing logo --></div> +<div class="tagline desktoponly"> +Small. Fast. 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There is no + server process that needs to be started, stopped, or configured. + There is + no need for an administrator to create a new database instance or assign + access permissions to users. + SQLite uses no configuration files. + Nothing needs to be done to tell the system that SQLite is running. + No actions are required to recover after a system crash or power failure. + There is nothing to troubleshoot. + <p> + SQLite just works. + <p> + Other more familiar database engines run great once you get them going. + But doing the initial installation and configuration can be + intimidatingly complex. +</blockquote> +<a name="serverless"></a> +<p><b>Serverless</b></p> +<blockquote> + <p> + <i>(See also the <a href="serverless.html">serverless</a> documentation page.)</i> + <p> + Most SQL database engines are implemented as a separate server + process. Programs that want to access the database communicate + with the server using some kind of interprocess communication + (typically TCP/IP) to send requests to the server and to receive + back results. SQLite does not work this way. With SQLite, the + process that wants to access the database reads and writes + directly from the database files on disk. There is no intermediary + server process. + <p> + There are advantages and disadvantages to being serverless. The + main advantage is that there is no separate server process + to install, setup, configure, initialize, manage, and troubleshoot. + This is one reason why SQLite is a "zero-configuration" database + engine. Programs that use SQLite require no administrative support + for setting up the database engine before they are run. Any program + that is able to access the disk is able to use an SQLite database. + <p> + On the other hand, a database engine that uses a server can provide + better protection from bugs in the client application - stray pointers + in a client cannot corrupt memory on the server. And because a server + is a single persistent process, it is able control database access with + more precision, allowing for finer grain locking and better concurrency. + <p> + Most SQL database engines are client/server based. Of those that are + serverless, SQLite is the only one that this author knows of that + allows multiple applications to access the same database at the same time. +</blockquote> +<a name="onefile"></a> +<p><b>Single Database File</b></p> +<blockquote> + An SQLite database is a single ordinary disk file that can be located + anywhere in the directory hierarchy. If SQLite can read + the disk file then it can read anything in the database. If the disk + file and its directory are writable, then SQLite can change anything + in the database. Database files can easily be copied onto a USB + memory stick or emailed for sharing. + <p> + Other SQL database engines tend to store data as a large collection of + files. Often these files are in a standard location that only the + database engine itself can access. This makes the data more secure, + but also makes it harder to access. Some SQL database engines provide + the option of writing directly to disk and bypassing the filesystem + altogether. This provides added performance, but at the cost of + considerable setup and maintenance complexity. +</blockquote> +<a name="onefile"></a> +<p><b>Stable Cross-Platform Database File</b></p> +<blockquote> + The SQLite file format is cross-platform. A database file written + on one machine can be copied to and used on a different machine with + a different architecture. Big-endian or little-endian, 32-bit or + 64-bit does not matter. All machines use the same file format. + Furthermore, the developers have pledged to keep the file format + stable and backwards compatible, so newer versions of SQLite can + read and write older database files. + <p> + Most other SQL database engines require you to dump and restore + the database when moving from one platform to another and often + when upgrading to a newer version of the software. +</blockquote> +<a name="small"></a> +<p><b>Compact</b></p> +<blockquote> + When optimized for size, the whole SQLite library with everything enabled + is <a href="footprint.html">less than 500KiB in size</a> + (as measured on an ix86 using the "size" + utility from the GNU compiler suite.) Unneeded features can be disabled + at compile-time to further reduce the size of the library to under + 300KiB if desired. + <p> + Most other SQL database engines are much larger than this. IBM boasts + that its recently released CloudScape database engine is "only" a 2MiB + jar file - an order of magnitude larger than SQLite even after it is + compressed! + Firebird boasts that its client-side library is only 350KiB. That's + as big as SQLite and does not even contain the database engine. + The Berkeley DB library from Oracle is 450KiB and it omits SQL + support, providing the programmer with only simple key/value pairs. +</blockquote> +<a name="typing"></a> +<p><b>Manifest typing</b></p> +<blockquote> + Most SQL database engines use static typing. A datatype is associated + with each column in a table and only values of that particular datatype + are allowed to be stored in that column. SQLite relaxes this restriction + by using manifest typing. + In manifest typing, the datatype is a property of the value itself, not + of the column in which the value is stored. + SQLite thus allows the user to store + any value of any datatype into any column regardless of the declared type + of that column. (There are some exceptions to this rule: An INTEGER + PRIMARY KEY column may only store integers. And SQLite attempts to coerce + values into the declared datatype of the column when it can.) + <p> + As far as we can tell, the SQL language specification allows the use + of manifest typing. Nevertheless, most other SQL database engines are + statically typed and so some people + feel that the use of manifest typing is a bug in SQLite. But the authors + of SQLite feel very strongly that this is a feature. The use of manifest + typing in SQLite is a deliberate design decision which has proven in practice + to make SQLite more reliable and easier to use, especially when used in + combination with dynamically typed programming languages such as Tcl and + Python. +</blockquote> +<a name="flex"></a> +<p><b>Variable-length records</b></p> +<blockquote> + Most other SQL database engines allocated a fixed amount of disk space + for each row in most tables. They play special tricks for handling + BLOBs and CLOBs which can be of wildly varying length. But for most + tables, if you declare a column to be a VARCHAR(100) then the database + engine will allocate + 100 bytes of disk space regardless of how much information you actually + store in that column. + <p> + SQLite, in contrast, use only the amount of disk space actually + needed to store the information in a row. If you store a single + character in a VARCHAR(100) column, then only a single byte of disk + space is consumed. (Actually two bytes - there is some overhead at + the beginning of each column to record its datatype and length.) + <p> + The use of variable-length records by SQLite has a number of advantages. + It results in smaller database files, obviously. It also makes the + database run faster, since there is less information to move to and from + disk. And, the use of variable-length records makes it possible for + SQLite to employ manifest typing instead of static typing. +</blockquote> +<a name="readable"></a> +<p><b>Readable source code</b></p> +<blockquote> + The source code to SQLite is designed to be readable and accessible to + the average programmer. All procedures and data structures and many + automatic variables are carefully commented with useful information about + what they do. Boilerplate commenting is omitted. +</blockquote> +<a name="vdbe"></a> +<p><b>SQL statements compile into virtual machine code</b></p> +<blockquote> + Every SQL database engine compiles each SQL statement into some kind of + internal data structure which is then used to carry out the work of the + statement. But in most SQL engines that internal data structure is a + complex web of interlinked structures and objects. In SQLite, the compiled + form of statements is a short program in a machine-language like + representation. Users of the database can view this + <a href="opcode.html">virtual machine language</a> + by prepending the <a href="lang_explain.html">EXPLAIN</a> keyword + to a query. + <p> + The use of a virtual machine in SQLite has been a great benefit to the + library's development. The virtual machine provides a crisp, well-defined + junction between the front-end of SQLite (the part that parses SQL + statements and generates virtual machine code) and the back-end (the + part that executes the virtual machine code and computes a result.) + The virtual machine allows the developers to see clearly and in an + easily readable form what SQLite is trying to do with each statement + it compiles, which is a tremendous help in debugging. + Depending on how it is compiled, SQLite also has the capability of + tracing the execution of the virtual machine - printing each + virtual machine instruction and its result as it executes. +</blockquote> +<a name="license"></a> +<p><b>Public domain</b></p> +<blockquote> + The source code for SQLite is in the public domain. No claim of copyright + is made on any part of the core source code. (The documentation and test + code is a different matter - some sections of documentation and test logic + are governed by open-source licenses.) All contributors to the + SQLite core software have signed affidavits specifically disavowing any + copyright interest in the code. This means that anybody is able to legally + do anything they want with the SQLite source code. + <p> + There are other SQL database engines with liberal licenses that allow + the code to be broadly and freely used. But those other engines are + still governed by copyright law. SQLite is different in that copyright + law simply does not apply. + <p> + The source code files for other SQL database engines typically begin + with a comment describing your legal rights to view and copy that file. + The SQLite source code contains no license since it is not governed by + copyright. Instead of a license, the SQLite source code offers a blessing: + <blockquote> + <i>May you do good and not evil<br> + May you find forgiveness for yourself and forgive others<br> + May you share freely, never taking more than you give.</i> + </blockquote> +</blockquote> +<a name="extensions"></a> +<p><b>SQL language extensions</b></p> +<blockquote> + SQLite provides a number of enhancements to the SQL language + not normally found in other database engines. + The EXPLAIN keyword and manifest typing have already been mentioned + above. SQLite also provides statements such as + <a href="lang_replace.html">REPLACE</a> and the + <a href="lang_conflict.html">ON CONFLICT</a> clause that allow for + added control over the resolution of constraint conflicts. + SQLite supports <a href="lang_attach.html">ATTACH</a> and + <a href="lang_detach.html">DETACH</a> commands that allow multiple + independent databases to be used together in the same query. + And SQLite defines APIs which allow the user to add new + <a href="c3ref/create_function.html">SQL functions</a> + and <a href="c3ref/create_collation.html">collating sequences</a>. +</blockquote> + +<p align="center"><small><i>This page last modified on <a href="https://sqlite.org/docsrc/honeypot" id="mtimelink" data-href="https://sqlite.org/docsrc/finfo/pages/different.in?m=95a3317bd2a3d0b7a">2022-01-20 21:38:08</a> UTC </small></i></p> + |