SQLite Learning、SQL Query Optimization In Multiple Rule

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. SQLite简介
. Sqlite安装
. SQLite Programing
. SQLite statements

1. SQLite简介

SQLite是一款轻型的数据库，是遵守ACID的关系型数据库管理系统，它包含在一个相对小的C库中。它是D.RichardHipp建立的公有领域项目。它的设计目标是嵌入式的，而且目前已经在很多嵌入式产品中使用了它，它占用资源非常的低，在嵌入式设备中，可能只需要几百K的内存就够了。它能够支持Windows/Linux/Unix等等主流的操作系统，同时能够跟很多程序语言相结合，比如 Tcl、C#、PHP、Java等，还有ODBC接口，同样比起Mysql、PostgreSQL这两款开源的世界著名数据库管理系统来讲，它的处理速度比他们都快
SQLite 支持跨平台，操作简单，能够使用很多语言直接创建数据库，而不象Access一样需要Office的支持。如果是个很小型的应用，或者你想做嵌入式开发，没有合适的数据库系统，那么可以考虑使用SQLite

0x1: SQLite原理

不像常见的客户-服务器范例，SQLite引擎不是个程序与之通信的独立进程，而是连接到程序中成为它的一个主要部分。所以主要的通信协议是在编程语言内的直接API调用。这在消耗总量、延迟时间和整体简单性上有积极的作用。整个数据库(定义、表、索引和数据本身)都在宿主主机上存储在一个单一的文件中。它的简单的设计是通过在开始一个事务的时候锁定整个数据文件而完成的

0x2: 功能特性

. ACID事务
. 零配置: 无需安装和管理配置(得益于非C/S架构的设计)
. 储存在单一磁盘文件中的一个完整的数据库(文件型数据库)
. 数据库文件可以在不同字节顺序的机器间自由的共享
. 支持数据库大小至2TB
. 足够小: 大致13万行C代码，4.43M
. 比一些流行的数据库在大部分普通数据库操作要快
. 简单API方式
. 包含TCL绑定, 同时通过Wrapper支持其他语言的绑定
. 良好注释的源代码, 并且有着90%以上的测试覆盖率
. 独立: 没有额外依赖
. 源码完全的开源，可以用于任何用途
. 支持多种开发语言，C、C++、PHP、Perl、Java、C#、Python、Ruby等

0x3: SQL语法支持

SQLite虽然很小巧，但是支持的SQL语句不会逊色于其他开源数据库，它支持的SQL包括

ATTACH DATABASE
BEGIN TRANSACTION
comment
COMMIT TRANSACTION
COPY
CREATE INDEX
CREATE TABLE
CREATE TRIGGER
CREATE VIEW
DELETE
DETACH DATABASE
DROP INDEX
DROP TABLE
DROP TRIGGER
DROP VIEW
END TRANSACTION
EXPLAIN
expression
INSERT
ON CONFLICT clause
PRAGMA
REPLACE
ROLLBACK TRANSACTION
SELECT
UPDATE

0x4: 数据类型

SQLite是无类型的，即typelessness(无类型)，我们可以保存任何类型的数据到所想要保存的任何表的任何列中，无论这列声明的数据类型是什么(除了字段类型为"Integer Primary Key"之外)，对于SQLite来说对字段不指定类型是完全有效的，如:

Create Table ex1(a, b, c);
//虽然SQLite允许忽略数据类型, 但是仍然建议在Create Table语句中指定数据类型. 因为数据类型对于和其他的程序员交流, 或者准备换掉的数据库引擎时能起到一个提示或帮助的作用

SQLite支持常见的数据类型，如:

CREATE TABLE ex2
a VARCHAR(),
b NVARCHAR(),
c TEXT,
d INTEGER,
e FLOAT,
f BOOLEAN,
g CLOB,
h BLOB,
i TIMESTAMP,
j NUMERIC(,)
k VARYING CHARACTER (),
l NATIONAL VARYING CHARACTER()

0x5: SQLite常用函数

The core functions shown below are available by default. Date & Time functions and aggregate functions are documented separately. An application may define additional functions written in C and added to the database engine using the sqlite3_create_function() API.

. abs(X)
The abs(X) function returns the absolute value of the numeric argument X. Abs(X) returns NULL if X is NULL. Abs(X) returns 0.0 if X is a string or blob that cannot be converted to a numeric value. If X is the integer - then abs(X) throws an integer overflow error since there is no equivalent positive -bit two complement value.

. changes()
The changes() function returns the number of database rows that were changed or inserted or deleted by the most recently completed INSERT, DELETE, or UPDATE statement, exclusive of statements in lower-level triggers. The changes() SQL function is a wrapper around the sqlite3_changes() C/C++ function and hence follows the same rules for counting changes.

. char(X1,X2,...,XN)
The char(X1,X2,...,XN) function returns a string composed of characters having the unicode code point values of integers X1 through XN, respectively.

. coalesce(X,Y,...)
The coalesce() function returns a copy of its first non-NULL argument, or NULL if all arguments are NULL. Coalesce() must have at least  arguments.

. glob(X,Y)
The glob(X,Y) function is equivalent to the expression "Y GLOB X". Note that the X and Y arguments are reversed in the glob() function relative to the infix GLOB operator. If the sqlite3_create_function() interface is used to override the glob(X,Y) function with an alternative implementation then the GLOB operator will invoke the alternative implementation.

. ifnull(X,Y)
The ifnull() function returns a copy of its first non-NULL argument, or NULL if both arguments are NULL. Ifnull() must have exactly  arguments. The ifnull() function is equivalent to coalesce() with two arguments.

. instr(X,Y)
The instr(X,Y) function finds the first occurrence of string Y within string X and returns the number of prior characters plus , or  if Y is nowhere found within X. Or, if X and Y are both BLOBs, then instr(X,Y) returns one more than the number bytes prior to the first occurrence of Y, or  if Y does not occur anywhere within X. If both arguments X and Y to instr(X,Y) are non-NULL and are not BLOBs then both are interpreted as strings. If either X or Y are NULL in instr(X,Y) then the result is NULL.

. hex(X)
The hex() function interprets its argument as a BLOB and returns a string which is the upper-case hexadecimal rendering of the content of that blob.

. last_insert_rowid()    The last_insert_rowid() function returns the ROWID of the last row insert from the database connection which invoked the function. The last_insert_rowid() SQL function is a wrapper around the sqlite3_last_insert_rowid() C/C++ interface function.

. length(X)
For a string value X, the length(X) function returns the number of characters (not bytes) in X prior to the first NUL character. Since SQLite strings do not normally contain NUL characters, the length(X) function will usually return the total number of characters in the string X. For a blob value X, length(X) returns the number of bytes in the blob. If X is NULL then length(X) is NULL. If X is numeric then length(X) returns the length of a string representation of X.

. like(X,Y)
. like(X,Y,Z)
The like() function is used to implement the "Y LIKE X [ESCAPE Z]" expression. If the optional ESCAPE clause is present, then the like() function is invoked with three arguments. Otherwise, it is invoked with two arguments only. Note that the X and Y parameters are reversed in the like() function relative to the infix LIKE operator. The sqlite3_create_function() interface can be used to override the like() function and thereby change the operation of the LIKE operator. When overriding the like() function, it may be important to override both the two and three argument versions of the like() function. Otherwise, different code may be called to implement the LIKE operator depending on whether or not an ESCAPE clause was specified.

. likelihood(X,Y)
The likelihood(X,Y) function returns argument X unchanged. The value Y in likelihood(X,Y) must be a floating point constant between 0.0 and 1.0, inclusive. The likelihood(X) function is a no-op that the code generator optimizes away so that it consumes no CPU cycles during run-time (that is, during calls to sqlite3_step()). The purpose of the likelihood(X,Y) function is to provide a hint to the query planner that the argument X is a boolean that is true with a probability of approximately Y. The unlikely(X) function is short-hand for likelihood(X,0.0625). The likely(X) function is short-hand for likelihood(X,0.9375).

. likely(X)    The likely(X) function returns the argument X unchanged. The likely(X) function is a no-op that the code generator optimizes away so that it consumes no CPU cycles at run-time (that is, during calls to sqlite3_step()). The purpose of the likely(X) function is to provide a hint to the query planner that the argument X is a boolean value that is usually true. The likely(X) function is equivalent to likelihood(X,0.9375). See also: unlikely(X).

. load_extension(X)
. load_extension(X,Y)
The load_extension(X,Y) function loads SQLite extensions out of the shared library file named X using the entry point Y. The result of load_extension() is always a NULL. If Y is omitted then the default entry point name is used. The load_extension() function raises an exception if the extension fails to load or initialize correctly.
The load_extension() function will fail if the extension attempts to modify or delete an SQL function or collating sequence. The extension can add new functions or collating sequences, but cannot modify or delete existing functions or collating sequences because those functions and/or collating sequences might be used elsewhere in the currently running SQL statement. To load an extension that changes or deletes functions or collating sequences, use the sqlite3_load_extension() C-language API.
//For security reasons, extension loaded is turned off by default and must be enabled by a prior call to sqlite3_enable_load_extension().

. lower(X)
The lower(X) function returns a copy of string X with all ASCII characters converted to lower case. The default built-in lower() function works for ASCII characters only. To do case conversions on non-ASCII characters, load the ICU extension.

. ltrim(X)
. ltrim(X,Y)
The ltrim(X,Y) function returns a string formed by removing any and all characters that appear in Y from the left side of X. If the Y argument is omitted, ltrim(X) removes spaces from the left side of X.

. max(X,Y,...)
The multi-argument max() function returns the argument with the maximum value, or return NULL if any argument is NULL. The multi-argument max() function searches its arguments from left to right for an argument that defines a collating function and uses that collating function for all string comparisons. If none of the arguments to max() define a collating function, then the BINARY collating function is used. Note that max() is a simple function when it has  or more arguments but operates as an aggregate function if given only a single argument.

. min(X,Y,...)
The multi-argument min() function returns the argument with the minimum value. The multi-argument min() function searches its arguments from left to right for an argument that defines a collating function and uses that collating function for all string comparisons. If none of the arguments to min() define a collating function, then the BINARY collating function is used. Note that min() is a simple function when it has  or more arguments but operates as an aggregate function if given only a single argument.

. nullif(X,Y)
The nullif(X,Y) function returns its first argument if the arguments are different and NULL if the arguments are the same. The nullif(X,Y) function searches its arguments from left to right for an argument that defines a collating function and uses that collating function for all string comparisons. If neither argument to nullif() defines a collating function then the BINARY is used.

. printf(FORMAT,...)
The printf(FORMAT,...) SQL function works like the sqlite3_mprintf() C-language function and the printf() function from the standard C library. The first argument is a format string that specifies how to construct the output string using values taken from subsequent arguments. If the FORMAT argument is missing or NULL then the result is NULL. The %n format is silently ignored and does not consume an argument. The %p format is an alias for %X. The %z format is interchangeable with %s. If there are too few arguments in the argument list, missing arguments are assumed to have a NULL value, which is translated into  or 0.0 for numeric formats or an empty string for %s.

. quote(X)
The quote(X) function returns the text of an SQL literal which is the value of its argument suitable for inclusion into an SQL statement. Strings are surrounded by single-quotes with escapes on interior quotes as needed. BLOBs are encoded as hexadecimal literals. Strings with embedded NUL characters cannot be represented as string literals in SQL and hence the returned string literal is truncated prior to the first NUL.

. random()
The random() function returns a pseudo-random integer between - and +.

. randomblob(N)
The randomblob(N) function return an N-byte blob containing pseudo-random bytes. If N is less than  then a -byte random blob is returned.
/*
Hint: applications can generate globally unique identifiers using this function together with hex() and/or lower() like this:
hex(randomblob(16))
lower(hex(randomblob(16)))
*/

. replace(X,Y,Z)
The replace(X,Y,Z) function returns a string formed by substituting string Z for every occurrence of string Y in string X. The BINARY collating sequence is used for comparisons. If Y is an empty string then return X unchanged. If Z is not initially a string, it is cast to a UTF- string prior to processing.

. round(X)
. round(X,Y)
The round(X,Y) function returns a floating-point value X rounded to Y digits to the right of the decimal point. If the Y argument is omitted, it is assumed to be .

. rtrim(X)
. rtrim(X,Y)
The rtrim(X,Y) function returns a string formed by removing any and all characters that appear in Y from the right side of X. If the Y argument is omitted, rtrim(X) removes spaces from the right side of X.

. soundex(X)
The soundex(X) function returns a string that is the soundex encoding of the string X. The string "?000" is returned if the argument is NULL or contains no ASCII alphabetic characters. This function is omitted from SQLite by default. It is only available if the SQLITE_SOUNDEX compile-time option is used when SQLite is built.

. sqlite_compileoption_get(N)
The sqlite_compileoption_get() SQL function is a wrapper around the sqlite3_compileoption_get() C/C++ function. This routine returns the N-th compile-time option used to build SQLite or NULL if N is out of range. See also the compile_options pragma.

. sqlite_compileoption_used(X)
The sqlite_compileoption_used() SQL function is a wrapper around the sqlite3_compileoption_used() C/C++ function. When the argument X to sqlite_compileoption_used(X) is a string which is the name of a compile-time option, this routine returns true () or false () depending on whether or not that option was used during the build.

. sqlite_source_id()
The sqlite_source_id() function returns a string that identifies the specific version of the source code that was used to build the SQLite library. The string returned by sqlite_source_id() begins with the date and time that the source code was checked in and is follows by an SHA1 hash that uniquely identifies the source tree. This function is an SQL wrapper around the sqlite3_sourceid() C interface.

. sqlite_version()
The sqlite_version() function returns the version string for the SQLite library that is running. This function is an SQL wrapper around the sqlite3_libversion() C-interface.

. substr(X,Y,Z)
. substr(X,Y)
The substr(X,Y,Z) function returns a substring of input string X that begins with the Y-th character and which is Z characters long. If Z is omitted then substr(X,Y) returns all characters through the end of the string X beginning with the Y-th. The left-most character of X is number . If Y is negative then the first character of the substring is found by counting from the right rather than the left. If Z is negative then the abs(Z) characters preceding the Y-th character are returned. If X is a string then characters indices refer to actual UTF- characters. If X is a BLOB then the indices refer to bytes.

. total_changes()
The total_changes() function returns the number of row changes caused by INSERT, UPDATE or DELETE statements since the current database connection was opened. This function is a wrapper around the sqlite3_total_changes() C/C++ interface.

. trim(X)
. trim(X,Y)
The trim(X,Y) function returns a string formed by removing any and all characters that appear in Y from both ends of X. If the Y argument is omitted, trim(X) removes spaces from both ends of X.

. typeof(X)
The typeof(X) function returns a string that indicates the datatype of the expression X: "null", "integer", "real", "text", or "blob".

. unlikely(X)
The unlikely(X) function returns the argument X unchanged. The unlikely(X) function is a no-op that the code generator optimizes away so that it consumes no CPU cycles at run-time (that is, during calls to sqlite3_step()). The purpose of the unlikely(X) function is to provide a hint to the query planner that the argument X is a boolean value that is usually not true. The unlikely(X) function is equivalent to likelihood(X, 0.0625).

. unicode(X)
The unicode(X) function returns the numeric unicode code point corresponding to the first character of the string X. If the argument to unicode(X) is not a string then the result is undefined.

. upper(X)
The upper(X) function returns a copy of input string X in which all lower-case ASCII characters are converted to their upper-case equivalent.

. zeroblob(N)
The zeroblob(N) function returns a BLOB consisting of N bytes of 0x00. SQLite manages these zeroblobs very efficiently. Zeroblobs can be used to reserve space for a BLOB that is later written using incremental BLOB I/O. This SQL function is implemented using the sqlite3_result_zeroblob() routine from the C/C++ interface.

Relevant Link:

http://www.sqlite.org/lang_corefunc.html
https://www.sqlite.org/c3ref/funclist.html
http://baike.baidu.com/view/19310.htm
http://zh.wikipedia.org/wiki/SQLite
http://www.sqlite.org/

2. Sqlite安装

SQLite 是一个开源的嵌入式关系数据库，实现自包容、零配置、支持事务的SQL数据库引擎。 其特点是高度便携、使用方便、结构紧凑、高效、可靠。 与其他数据库管理系统不同，SQLite 的安装和运行非常简单，在大多数情况下 - 只要确保SQLite的二进制文件存在即可开始创建、连接和使用数据库

. SQLite on Windows
http://www.sqlite.org/download.html
下载 Windows 下的预编译二进制文件包：
sqlite-shell-win32-x86-<build#>.zip
sqlite-dll-win32-x86-<build#>.zip
注意: <build#> 是 sqlite 的编译版本号
将 zip 文件解压到你的磁盘，并将解压后的目录添加到系统的 PATH 变量中，以方便在命令行中执行 sqlite 命令。
可选: 如果你计划发布基于 sqlite 数据库的应用程序，你还需要下载源码以便编译和利用其 API
sqlite-amalgamation-<build#>.zip

. SQLite on Linux
/* For Debian or Ubuntu /*
$ sudo apt-get install sqlite3 sqlite3-dev

/* For RedHat, CentOS, or Fedora/*
$ yum install SQLite3 sqlite3-dev

0x1: 创建首个 SQLite 数据库

. 在命令行窗口中输入如下命令来创建一个名为  test.db 的数据库。
sqlite3 test.db

. 创建表
create table mytable(id integer primary key, value text);
//该表包含一个名为 id 的主键字段和一个名为 value 的文本字段

. 接下来往表里中写入一些数据
insert into mytable(id, value) values(, 'Micheal');
insert into mytable(id, value) values(, 'Jenny');
insert into mytable(value) values('Francis');
insert into mytable(value) values('Kerk');

. 查询数据
select * from test;

. 设置格式化查询结果
.mode column;    //.mode column 将设置为列显示模式
.header on;    //.header 将显示列名
select * from test;

. 创建视图
create view nameview as select * from mytable;

. 创建索引
create index test_idx on mytable(value);

Relevant Link:

http://www.oschina.net/question/12_53183

2. SQLite Programing

0x1: 用PHP操作sqlite数据库

//下面的 PHP 代码段将用于在先前创建的数据库中创建一个表
<?php
    class MyDB extends SQLite3
    {
        function __construct()
        {
            $this->open('test.db');
        }
    }

    $db = new MyDB();
    if(!$db)
    {
        echo $db->lastErrorMsg();
    }
    else
    {
        echo "Opened database successfully\n";
    }

    $sql =<<<EOF
        CREATE TABLE COMPANY
        (ID INT PRIMARY KEY     NOT NULL,
        NAME           TEXT    NOT NULL,
        AGE            INT     NOT NULL,
        ADDRESS        CHAR(),
        SALARY         REAL);
    EOF;

    $ret = $db->exec($sql);
    if(!$ret)
    {
        echo $db->lastErrorMsg();
    }
    else
    {
        echo "Table created successfully\n";
    }
    $db->close();
?>

0x2: 使用linux下的C操作SQLite

#include <stdio.h>
#include <sqlite3.h>

int main( void )
{
    sqlite3 *db = NULL;
    char *zErrMsg = ;
    int rc;

    //打开指定的数据库文件,如果不存在将创建一个同名的数据库文件
    rc = sqlite3_open("littlehann.db", &db);
    if( rc )
    {
        fprintf(stderr, "Can't open database: %s\n", sqlite3_errmsg(db));
        sqlite3_close(db);
        exit();
    }
    else printf("You have opened a sqlite3 database named littlehann.db successfully!\nCongratulations! Have fun ! ^-^ \n");
    sqlite3_close(db); //关闭数据库
    return ;
}
//gcc -o test test.c -lsqlite3

Relevant Link:

http://www.w3cschool.cc/sqlite/sqlite-php.html
http://www.w3cschool.cc/sqlite/sqlite-tutorial.html

4. SQLite statements

从安全攻防的角度来说，SQL预编译statements可以有效防御SQL Injection注入攻击，从性能的角度来看，将SQL语句预编译为一个二进制的形式直接加载进内存中可以大幅度提高SQL查询的性能

Relevant Link:

http://php.net/manual/en/sqlite3.prepare.php

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