Home Database Mysql Tutorial 摘抄:mysql set names和set

摘抄:mysql set names和set

Jun 07, 2016 pm 03:40 PM
mysql set introduce first

首先介绍下 三个MySQL的”环境变量”设置命令及其作用: character_set_client: MySQL服务器, 客户端的编码集 character_set_connection: 传输给MySQL服务器的时候的编码集 character_set_results: 期望MySQL返回的结果的编码集 比如, 通过使用”SET NAME

      首先介绍下三个MySQL的”环境变量”设置命令及其作用:

  • character_set_client:          MySQL服务器, 客户端的编码集
  • character_set_connection:传输给MySQL服务器的时候的编码集
  • character_set_results:       期望MySQL返回的结果的编码集

  比如, 通过使用”SET NAMES utf8″, 就告诉服务器, 我用的是utf-8编码, 我希望你也给我返回utf-8编码的查询结果. 

      一般情况下, 使用”SET NAMES”就足够了, 也是可以保证正确的. 那么为什么手册又要说推荐使用mysqli_set_charset呢? 

  首先, 我们看看mysqli_set_charset到底做了什么(注意星号注释处, mysql_set_charset类似):

 
  //php-5.2.11-SRC/ext/mysqli/mysqli_nonapi.c line 342 
  PHP_FUNCTION(mysqli_set_charset) 
  { 
  MY_MYSQL *mysql; 
  zval *mysql_link; 
  char *cs_name = NULL; 
  unsigned int len; 
  if (zend_parse_method_parameters(ZEND_NUM_ARGS() TSRMLS_CC, getThis() 
  , "Os", &mysql_link, mysqli_link_class_entry, &cs_name, &len) == FAILURE) { 
  return; 
  } 
  MYSQLI_FETCH_RESOURCE(mysql, MY_MYSQL*, &mysql_link, "mysqli_link" 
  , MYSQLI_STATUS_VALID); 
  if (mysql_set_character_set(mysql->mysql, cs_name)) { 
  //** 调用libmysql的对应函数 
  RETURN_FALSE; 
  } 
  RETURN_TRUE; 
   } 
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    那mysql_set_character_set又做了什么呢?

 
  //mysql-5.1.30-SRC/libmysql/client.c, line 3166: 
  int STDCALL mysql_set_character_set(MYSQL *mysql, const char *cs_name) 
  { 
  struct charset_info_st *cs; 
  const char *save_csdir= charsets_dir; 
  if (mysql->options.charset_dir) 
  charsets_dir= mysql->options.charset_dir; 
  if (strlen(cs_name) charset= cs; 
  } 
  } 
  //以下省略 
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 我们可以看到, mysqli_set_charset除了做了”SET NAMES”以外, 还多做了一步: 

 
  sprintf(buff, "SET NAMES %s", cs_name); 
  if (!mysql_real_query(mysql, buff, strlen(buff))) 
  { 
  mysql->charset= cs; 
  } 
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       而对于mysql这个核心结构的成员charset又有什么作用呢? 
  这就要说说mysql_real_escape_string()了, 这个函数和mysql_escape_string的区别就是, 它会考虑”当前”字符集. 那么这个当前字符集从哪里来呢? 
  对了, 你猜的没错, 就是mysql->charset. 
  mysql_real_string在判断宽字符集的字符的时候, 就根据这个成员变量来分别采用不同的策略, 比如如果是utf-8, 那么就会采用libmysql/ctype-utf8.c. 
  看个实例, 默认mysql连接字符集是latin-1, (经典的5c问题): 

 
  <?php   $db = mysql_connect(&#39;localhost:3737&#39;, &#39;root&#39; ,&#39;123456&#39;); 
  mysql_select_db("test"); 
  $a = "\x91\x5c";//"慭"的gbk编码, 低字节为5c, 也就是ascii中的"\" 
  var_dump(addslashes($a)); 
  var_dump(mysql_real_escape_string($a, $db)); 
  mysql_query("set names gbk"); 
  var_dump(mysql_real_escape_string($a, $db)); 
  mysql_set_charset("gbk"); 
  var_dump(mysql_real_escape_string($a, $db)); 
  ?> 
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      因为, “慭”的gbk编码低字节为5c, 也就是ascii中的”\”, 而因为除了mysql(i)_set_charset影响mysql->charset以外, 其他时刻mysql->charset都为默认值,

      所以, 结果就是: 

 
  $ php -f 5c.php 
  string(3) "慭\" 
  string(3) "慭\" 
  string(3) "慭\" 
  string(2) "慭" 
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 个中细节有待进一步验证。原文适当修改。文章摘至:深入理解mysql SET NAMES和mysql(i)_set_charset
 

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