php分享十五：php的数据库操作

一：术语解释：

What is an Extension?

API和扩展不能理解为一个东西，因为扩展不一定暴露一个api给用户

The PDO MySQL driver extension, for example, does not expose an API to the PHP programmer, but provides an interface to the PDO layer above it.

The terms API and extension should not be taken to mean the same thing, as an extension may not necessarily expose an API to the programmer.

参考：http://php.net/manual/zh/mysqlinfo.terminology.php

二：扩展选择：

ext/mysqli	PDO_MySQL	ext/mysql
PHP version introduced	5.0	5.1	2.0
Included with PHP 5.x	Yes	Yes	Yes
Included with PHP 7.x	Yes	Yes	No
Development status	Active	Active	Maintenance only in 5.x; removed in 7.x
Lifecycle	Active	Active	Deprecated in 5.x; removed in 7.x
Recommended for new projects	Yes	Yes	No
OOP Interface	Yes	Yes	No
Procedural Interface	Yes	No	Yes
API supports non-blocking, asynchronous queries with mysqlnd	Yes	No	No
Persistent Connections	Yes	Yes	Yes
API supports Charsets	Yes	Yes	Yes
API supports server-side Prepared Statements	Yes	Yes	No
API supports client-side Prepared Statements	No	Yes	No
API supports Stored Procedures	Yes	Yes	No
API supports Multiple Statements	Yes	Most	No
API supports Transactions	Yes	Yes	No
Transactions can be controlled with SQL	Yes	Yes	Yes
Supports all MySQL 5.1+ functionality	Yes	Most	No

三：选择mysql驱动（Choosing a library）

mysqli,mysql,pdo底层都是用c写的，有两种底层c库可以使用（mysqlnd library 和 libmysqlclient library），通过编译参数可以更改区别：

mysqlnd更胜一筹；

从php5.3开始，mysqlnd成为php的一部分发布，mysqlnd提供的高级功能有：lazy connections and query caching （这两个功能libmysqlclient library是没有的）

编译配置：

// Recommended, compiles with mysqlnd
$ ./configure --with-mysqli=mysqlnd --with-pdo-mysql=mysqlnd --with-mysql=mysqlnd

// Alternatively recommended, compiles with mysqlnd as of PHP 5.4
$ ./configure --with-mysqli --with-pdo-mysql --with-mysql

// Not recommended, compiles with libmysqlclient
$ ./configure --with-mysqli=/path/to/mysql_config --with-pdo-mysql=/path/to/mysql_config --with-mysql=/path/to/mysql_config

注意：可以分别指定mysqli， mysql， pdo 扩展的底层c库

	MySQL native driver (mysqlnd)	MySQL client server library (libmysqlclient)
Part of the PHP distribution	Yes	No
PHP version introduced	5.3.0	N/A
License	PHP License 3.01	Dual-License
Development status	Active	Active
Lifecycle	No end announced	No end announced
PHP 5.4 and above; compile default (for all MySQL extensions)	Yes	No
PHP 5.3; compile default (for all MySQL extensions)	No	Yes
Compression protocol support	Yes (5.3.1+)	Yes
SSL support	Yes (5.3.3+)	Yes
Named pipe support	Yes (5.3.4+)	Yes
Non-blocking, asynchronous queries	Yes	No
Performance statistics	Yes	No
LOAD LOCAL INFILE respects the open_basedir directive	Yes	No
Uses PHP's native memory management system (e.g., follows PHP memory limits)	Yes	No
Return numeric column as double (COM_QUERY)	Yes	No
Return numeric column as string (COM_QUERY)	Yes	Yes
Plugin API	Yes	Limited
Read/Write splitting for MySQL Replication	Yes, with plugin	No
Load Balancing	Yes, with plugin	No
Fail over	Yes, with plugin	No
Lazy connections	Yes, with plugin	No
Query caching	Yes, with plugin	No
Transparent query manipulations (E.g., auto-EXPLAIN or monitoring)	Yes, with plugin	No

	MySQL native driver (mysqlnd)	MySQL client server library (libmysqlclient)
Part of the PHP distribution	Yes	No
PHP version introduced	5.3.0	N/A
License	PHP License 3.01	Dual-License
Development status	Active	Active
Lifecycle	No end announced	No end announced
PHP 5.4 and above; compile default (for all MySQL extensions)	Yes	No
PHP 5.3; compile default (for all MySQL extensions)	No	Yes
Compression protocol support	Yes (5.3.1+)	Yes
SSL support	Yes (5.3.3+)	Yes
Named pipe support	Yes (5.3.4+)	Yes
Non-blocking, asynchronous queries	Yes	No
Performance statistics	Yes	No
LOAD LOCAL INFILE respects the open_basedir directive	Yes	No
Uses PHP's native memory management system (e.g., follows PHP memory limits)	Yes	No
Return numeric column as double (COM_QUERY)	Yes	No
Return numeric column as string (COM_QUERY)	Yes	Yes
Plugin API	Yes	Limited
Read/Write splitting for MySQL Replication	Yes, with plugin	No
Load Balancing	Yes, with plugin	No
Fail over	Yes, with plugin	No
Lazy connections	Yes, with plugin	No
Query caching	Yes, with plugin	No
Transparent query manipulations (E.g., auto-EXPLAIN or monitoring)

四：mysql字符集设置

字符设置必须用特定的函数来设置，而不能用query来处理

<?php

$mysqli = new mysqli("localhost", "my_user", "my_password", "world");

// Will NOT affect $mysqli->real_escape_string();
$mysqli->query("SET NAMES utf8");

// Will NOT affect $mysqli->real_escape_string();
$mysqli->query("SET CHARACTER SET utf8");

// But, this will affect $mysqli->real_escape_string();
$mysqli->set_charset('utf8');

// But, this will NOT affect it (utf-8 vs utf8) -- don't use dashes here
$mysqli->set_charset('utf-8');

?>

注意：

设置utf8编码时，不能用utf-8,而是utf8（因为在mysql中设置编码不能包含-）

Note: Possible UTF-8 confusion

Because character set names in MySQL do not contain dashes, the string "utf8" is valid in MySQL to set the character set to UTF-8. The string "utf-8" is not valid, as using "utf-8" will fail to change the character set.