我使用http://dev.mysql.com/downloads/mysql上的安装程序安装了MySQL服务器。然后，按照几个指南的说明，我想通过以下命令安装mysql gem。
sudo gem install mysql
这不起作用，并输出以下内容。
Building native extensions. This could take a while...
ERROR: Error installing mysql:
ERROR: Failed to build gem native extension.
/Users/luzi/.rvm/rubies/ruby-1.9.3-p429/bin/ruby extconf.rb --with-mysql-dir=/usr/local/mysql/
checking for mysql_ssl_set()... *** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers. Check the mkmf.log file for more
details. You may need configuration options.
Provided configuration options:
--with-opt-dir
--with-opt-include
--without-opt-include=${opt-dir}/include
--with-opt-lib
--without-opt-lib=${opt-dir}/lib
--with-make-prog
--without-make-prog
--srcdir=.
--curdir
--ruby=/Users/luzi/.rvm/rubies/ruby-1.9.3-p429/bin/ruby
--with-mysql-config
--without-mysql-config
/Users/luzi/.rvm/rubies/ruby-1.9.3-p429/lib/ruby/1.9.1/mkmf.rb:381:in `try_do': The compiler failed to generate an executable file. (RuntimeError)
You have to install development tools first.
from /Users/luzi/.rvm/rubies/ruby-1.9.3-p429/lib/ruby/1.9.1/mkmf.rb:461:in `try_link0'
from /Users/luzi/.rvm/rubies/ruby-1.9.3-p429/lib/ruby/1.9.1/mkmf.rb:476:in `try_link'
from /Users/luzi/.rvm/rubies/ruby-1.9.3-p429/lib/ruby/1.9.1/mkmf.rb:619:in `try_func'
from /Users/luzi/.rvm/rubies/ruby-1.9.3-p429/lib/ruby/1.9.1/mkmf.rb:894:in `block in have_func'
from /Users/luzi/.rvm/rubies/ruby-1.9.3-p429/lib/ruby/1.9.1/mkmf.rb:790:in `block in checking_for'
from /Users/luzi/.rvm/rubies/ruby-1.9.3-p429/lib/ruby/1.9.1/mkmf.rb:284:in `block (2 levels) in postpone'
from /Users/luzi/.rvm/rubies/ruby-1.9.3-p429/lib/ruby/1.9.1/mkmf.rb:254:in `open'
from /Users/luzi/.rvm/rubies/ruby-1.9.3-p429/lib/ruby/1.9.1/mkmf.rb:284:in `block in postpone'
from /Users/luzi/.rvm/rubies/ruby-1.9.3-p429/lib/ruby/1.9.1/mkmf.rb:254:in `open'
from /Users/luzi/.rvm/rubies/ruby-1.9.3-p429/lib/ruby/1.9.1/mkmf.rb:280:in `postpone'
from /Users/luzi/.rvm/rubies/ruby-1.9.3-p429/lib/ruby/1.9.1/mkmf.rb:789:in `checking_for'
from /Users/luzi/.rvm/rubies/ruby-1.9.3-p429/lib/ruby/1.9.1/mkmf.rb:893:in `have_func'
from extconf.rb:45:in `<main>'
Gem files will remain installed in /Users/luzi/.rvm/gems/ruby-1.9.3-p429/gems/mysql-2.9.1 for inspection.
Results logged to /Users/luzi/.rvm/gems/ruby-1.9.3-p429/gems/mysql-2.9.1/ext/mysql_api/gem_make.out
我多次重新安装了ruby 1.9.3，同时也安装了XCode命令行工具。我也使用homebrew安装了mysql服务器（没有带任何东西）。
我还尝试了一些命令的选项，比如
--with-mysql-dir=/usr/local/mysql和--with-mysql-config=/usr/local/mysql/bin/mysql_config。传递标志（sudo env ARCHFLAGS="-arch x86_64" gem install mysql）也没有帮助。更新：
我还尝试了mysql2 gem，结果出现了同样的错误，可能是因为mysql2 gem依赖于mysql gem。
更新2：
mkmf.log的内容："/opt/local/bin/gcc-apple-4.2 -o conftest -I/Users/luzi/.rvm/rubies/ruby-1.9.3-p429/include/ruby-1.9.1/x86_64-darwin12.4.0 -I/Users/luzi/.rvm/rubies/ruby-1.9.3-p429/include/ruby-1.9.1/ruby/backward -I/Users/luzi/.rvm/rubies/ruby-1.9.3-p429/include/ruby-1.9.1 -I. -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE -I/opt/local/include -I/usr/local/mysql/include -Wno-null-conversion -Os -g -fno-strict-aliasing -arch x86_64 -O3 -ggdb -Wall -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Wpointer-arith -Wwrite-strings -Wdeclaration-after-statement -Wshorten-64-to-32 -Wimplicit-function-declaration -fno-common -pipe conftest.c -L. -L/Users/luzi/.rvm/rubies/ruby-1.9.3-p429/lib -L/opt/local/lib -L. -L/usr/local/lib -L/opt/local/lib -L/usr/local/mysql/lib -lmysqlclient -lruby.1.9.1 -lpthread -ldl -lobjc "
cc1: error: unrecognized command line option "-Wno-null-conversion"
checked program was:
/* begin */
1: #include "ruby.h"
2:
3: int main(int argc, char **argv)
4: {
5: return 0;
6: }
/* end */
rvm @global do gem install mysql也可以工作。 - lulezi