请帮助我了解如何在MySQL utf8mb4字段中处理像emoji表情这样的多字节字符。

请参阅下面的简单测试SQL来说明挑战。

/* Clear Previous Test */
DROP TABLE IF EXISTS `emoji_test`;
DROP TABLE IF EXISTS `emoji_test_with_unique_key`;

/* Build Schema */
CREATE TABLE `emoji_test` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `string` varchar(191) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT '',
  `status` tinyint(1) NOT NULL DEFAULT '1',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
CREATE TABLE `emoji_test_with_unique_key` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `string` varchar(191) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT '',
  `status` tinyint(1) NOT NULL DEFAULT '1',
  PRIMARY KEY (`id`),
  UNIQUE KEY `idx_string_status` (`string`,`status`) USING BTREE
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

/* INSERT data */
# Expected Result is successful insert for each of these.
# However some fail. See comments.
INSERT INTO emoji_test (`string`, `status`) VALUES ('🌶', 1);                   # SUCCESS
INSERT INTO emoji_test (`string`, `status`) VALUES ('🌮', 1);                   # SUCCESS
INSERT INTO emoji_test (`string`, `status`) VALUES ('🌮🌶', 1);                 # SUCCESS
INSERT INTO emoji_test (`string`, `status`) VALUES ('🌶🌮', 1);                 # SUCCESS
INSERT INTO emoji_test_with_unique_key (`string`, `status`) VALUES ('🌶', 1);   # SUCCESS
INSERT INTO emoji_test_with_unique_key (`string`, `status`) VALUES ('🌮', 1);   # FAIL: Duplicate entry '?-1' for key 'idx_string_status'
INSERT INTO emoji_test_with_unique_key (`string`, `status`) VALUES ('🌮🌶', 1); # SUCCESS
INSERT INTO emoji_test_with_unique_key (`string`, `status`) VALUES ('🌶🌮', 1); # FAIL: Duplicate entry '??-1' for key 'idx_string_status'

/* Test data */

    /* Simple Table */
SELECT * FROM emoji_test WHERE `string` IN ('🌶','🌮','🌮🌶','🌶🌮'); # SUCCESS (all 4 are found)
SELECT * FROM emoji_test WHERE `string` IN ('🌶');                     # FAIL: Returns both 🌶 and 🌮
SELECT * FROM emoji_test WHERE `string` IN ('🌮');                     # FAIL: Returns both 🌶 and 🌮
SELECT * FROM emoji_test;                                              # SUCCESS (all 4 are found)

    /* Table with Unique Key */
SELECT * FROM emoji_test_with_unique_key WHERE `string` IN ('🌶','🌮','🌮🌶','🌶🌮'); # FAIL: Only 2 are found (due to insert errors above)
SELECT * FROM emoji_test_with_unique_key WHERE `string` IN ('🌶');                     # SUCCESS
SELECT * FROM emoji_test_with_unique_key WHERE `string` IN ('🌮');                     # FAIL: 🌶 found instead of 🌮
SELECT * FROM emoji_test_with_unique_key;     

我对了解导致上述FAILs的原因以及如何解决此问题很感兴趣。

具体来说：

1. 为什么选择一个多字节字符会返回 任何 多字节字符的结果？
2. 如何配置索引来处理多字节字符而不是?？
3. 您是否可以CREATE TABLE通过使所有测试查询成功返回的方式建议对上面的第二个（具有唯一键的）进行更改？