mysql concat 不同字元集,為什麼CONCAT（）不默認為MySQL中的默認字元集？

What is the reason, that using CONCAT() in pure UTF-8 environment MySQL still treats concatenated string (when some col in expression is for example int or date) as some other charset (probably Latin-1)?

是什麼原因，在純UTF-8環境中使用CONCAT()MySQL仍然將連接字元串(當表達式中的某些col為例如int或date)視為其他字元集(可能是Latin-1)？

MySQL environment seen from client (\s):

從客戶端看到的MySQL環境(\ s)：

Server characterset: utf8

Db characterset: utf8

Client characterset: utf8

Conn. characterset: utf8

Test dataset:

測試數據集：

CREATE TABLE `utf8_test` (

`id` int(10) unsigned NOT NULL auto_increment,

`title` varchar(50) collate utf8_estonian_ci default NULL,

`year` smallint(4) unsigned NOT NULL default '0',

PRIMARY KEY (`id`)

) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_estonian_ci;

INSERT INTO utf8_test VALUES (1, 'Õäöüšž', 2011);

This query is good:

這個查詢很好：

SELECT id, title FROM utf8_test;

This one turns utf-8 flag off (already in MySQL, AFIU):

這個關閉utf-8標志(已經在MySQL，AFIU)：

SELECT CONCAT(id, title) FROM utf8_test;

From mysql-client everything seems fine, because it is set to show chars as UTF-8, but when running through perl DBI, all results of queries having CONCAT() inside don't have utf-8 flag set. Example code:

從mysql-client看，一切似乎都很好，因為它被設置為將字元顯示為UTF-8，但是當通過perl DBI運行時，所有內部具有CONCAT()的查詢結果都沒有設置utf-8標志。示例代碼：

#!/usr/bin/perl

use strict;

use utf8::all;

use Encode qw(is_utf8);

my $dbh = your_db_connect_routine('test');

my $str = $dbh->selectrow_array('SELECT CONCAT(id, title) FROM utf8_test');

print "CONCAT: False\n" unless ( is_utf8($str) );

my $str = $dbh->selectrow_array('SELECT title FROM utf8_test');

print "NO CONCAT: False\n" unless ( is_utf8($str) );

There is at least two workarounds i know

我知道至少有兩種解決方法

quering with CAST() SELECT CONCAT( CAST(id AS CHAR CHARACTER SET utf8), title) FROM utf8_test

使用CAST()SELECT CONCAT(CAST(id AS CHAR CHARACTER SET utf8)，標題)從utf8_test查詢

using $str = Encode::_utf8_on($str) (is considered as bad practice?)

使用$ str = Encode :: _ utf8_on($ str)(被認為是不好的做法？)

but i am asking: why it is in MySQL so? Should i consider it as bug or feature?

但我在問：為什麼它在MySQL中呢？我應該將其視為錯誤或功能嗎？

2 個解決方案

#1

18

It's a well known bug in MySQL. It's fixed in MySQL 5.5

這是MySQL中一個眾所周知的錯誤。它已在MySQL 5.5中修復

請參閱：http：//bugs.mysql.com/bug.php？id = 12030

The issue stems from concatenating an integer with a varchar.

問題源於將整數與varchar連接起來。

The work around is to cast the id (integer) first to a char, and then concatenate, ie:

解決方法是首先將id(整數)轉換為char，然後連接，即：

SELECT CONCAT(cast(id as char), title) FROM utf8_test

#2

It probably is DBD::mysql issue/peculiarity. Try enabling utf8 in database handle as described in POD for DBD::mysql (mysql_enable_utf8 part).

它可能是DBD :: mysql問題/特殊性。嘗試在數據庫句柄中啟用utf8，如POD for DBD :: mysql(mysql_enable_utf8 part)中所述。

This old (Perl 5.8 times) article can also help.

這篇舊的(Perl 5.8次)文章也可以提供幫助。