mysql's collation roughly means character sorting.
First, characters are inherently size-insensitive, so a rule of character order is required for character >, =, <operations.collation does this either by setting the character order of a table or by setting the character order of a field separately.A character type that has multiple character orders, such as:

Below is the character order for UTF8.

utf8_general_ci utf8    33  Yes Yes 1
utf8_bin    utf8    83      Yes 1
utf8_unicode_ci utf8    192     Yes 8
utf8_icelandic_ci   utf8    193     Yes 8
utf8_latvian_ci utf8    194     Yes 8
utf8_romanian_ci    utf8    195     Yes 8
utf8_slovenian_ci   utf8    196     Yes 8
utf8_polish_ci  utf8    197     Yes 8
utf8_estonian_ci    utf8    198     Yes 8
utf8_spanish_ci utf8    199     Yes 8
utf8_swedish_ci utf8    200     Yes 8
utf8_turkish_ci utf8    201     Yes 8
utf8_czech_ci   utf8    202     Yes 8
utf8_danish_ci  utf8    203     Yes 8
utf8_lithuanian_ci  utf8    204     Yes 8
utf8_slovak_ci  utf8    205     Yes 8
utf8_spanish2_ci    utf8    206     Yes 8
utf8_roman_ci   utf8    207     Yes 8
utf8_persian_ci utf8    208     Yes 8
utf8_esperanto_ci   utf8    209     Yes 8
utf8_hungarian_ci   utf8    210     Yes 8
utf8_sinhala_ci utf8    211     Yes 8
utf8_german2_ci utf8    212     Yes 8
utf8_croatian_ci    utf8    213     Yes 8
utf8_unicode_520_ci utf8    214     Yes 8
utf8_vietnamese_ci  utf8    215     Yes 8
utf8_general_mysql500_ci    utf8    223     Yes 1

mysql character order follows naming conventions
With_ci (indicating case insensitive)
With_cs (case sensitive)
With_bin (for comparison with coded values)

For example:

CREATE TABLE `issue_message` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `content` varchar(255) NOT NULL,
  PRIMARY KEY (`id`),
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

The two SQLs below this table will produce the same result

select * from issue_message where content = 'Yes'
select * from issue_message where content = 'yes'

If you change to the following definition:

CREATE TABLE `issue_message` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `content` varchar(255) NOT NULL COLLATE utf8_bin,
  PRIMARY KEY (`id`),
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

Then the two sql results will be different.

Therefore, if character case is sensitive, it is best to set the default utf8_general_ci in the database to utf8_bin.