PHP将MySQL错误写入文件

How would I write a MySQL error to a file instead of displaying it to the user?

here is what I have so far...

if (!mysql_query($sql_query,$connection))
  {
  die('Error: ' . mysql_error());
  }
echo "Success!";

You can use the error_log function in php for that.

error_log("You messed up!", 3, "/var/tmp/my-errors.log");

Edit: so in your case this would look like the following (although i would use a different if statement)

if (!mysql_query($sql_query,$connection))
{
    error_log(mysql_error() . "
", 3, "/var/tmp/my-errors.log");
}
echo "Success!";

Firstly, you should not use die if you do not want to display your error message to the user.

Secondly, instead of using die, you must log your error message into a file. If you are using some logging library, you may output the error to some log, else you may want to have a look at File handling in PHP.

Link - http://davidwalsh.name/basic-php-file-handling-create-open-read-write-append-close-delete

Use error_log, or fopen/fwrite/fclose/etc.

I often use create my own error handler with something like set_error_handler in PHP and use trigger_error to capture ALL errors and write them to file. This may be a better scenario for you; rather than writing numerous error_log()'s, you can just create an error handler function and then use trigger_error.