请参阅mysql手册，Unicode字符集部分:

For any Unicode character set, operations performed using the _general_ci collation are faster than those for the _unicode_ci collation. For example, comparisons for the utf8_general_ci collation are faster, but slightly less correct, than comparisons for utf8_unicode_ci. The reason for this is that utf8_unicode_ci supports mappings such as expansions; that is, when one character compares as equal to combinations of other characters. For example, in German and some other languages “ß” is equal to “ss”. utf8_unicode_ci also supports contractions and ignorable characters. utf8_general_ci is a legacy collation that does not support expansions, contractions, or ignorable characters. It can make only one-to-one comparisons between characters.

因此，总的来说，utf_general_ci使用的比较集比utf_unicode_ci更小，更不正确(根据标准)，后者应该实现整个标准。general_ci集将更快，因为要做的计算更少。

上面的注释表明没有理由使用utf8_general*。然而，对于日本人来说，这可能不是真的。

在MariaDB中，utf8mb4_ja_0900_as_cs不可用，因此必须使用unicode或通用选项之一。然而，unicode对待浊音和浊音等是一样的。例如，びよういん(美容师)被视为等同于びょういん(医院)。这显然是不正确的行为。

> select strcmp('が', 'か' collate utf8mb4_unicode_ci); #0
> strcmp('びよういん', 'びょういん' collate utf8mb4_unicode_520_ci); #0 

而将军给出

> select strcmp('が', 'か' collate utf8mb4_general_ci); #1

换句话说，unicode对浊音假名和浊音假名一视同仁。在我看来，这并不可取。

编辑:使用uca1400_ai_cs可能更好，它在MariaDB的新版本中可用，并使上述排序正确。

我想知道使用utf8_general_ci和utf8_unicode_ci之间的性能差异是什么，但我没有在互联网上找到任何基准测试，所以我决定自己创建基准测试。

我创建了一个非常简单的50万行表:

CREATE TABLE test(
  ID INT(11) DEFAULT NULL,
  Description VARCHAR(20) DEFAULT NULL
)
ENGINE = INNODB
CHARACTER SET utf8
COLLATE utf8_general_ci;

然后我通过运行这个存储过程，用随机数据填充它:

CREATE PROCEDURE randomizer()
BEGIN
  DECLARE i INT DEFAULT 0;
  DECLARE random CHAR(20) ;
  theloop: loop
    SET random = CONV(FLOOR(RAND() * 99999999999999), 20, 36);
    INSERT INTO test VALUES (i+1, random);
    SET i=i+1;
    IF i = 500000 THEN
      LEAVE theloop;
    END IF;
  END LOOP theloop;
END

然后我创建了以下存储过程来测试简单的SELECT, SELECT with LIKE和排序(SELECT with ORDER BY):

CREATE PROCEDURE benchmark_simple_select()
BEGIN
  DECLARE i INT DEFAULT 0;
  theloop: loop
    SELECT *
    FROM test
    WHERE Description = 'test' COLLATE utf8_general_ci;
    SET i = i + 1;
    IF i = 30 THEN
      LEAVE theloop;
    END IF;
  END LOOP theloop;
END;

CREATE PROCEDURE benchmark_select_like()
BEGIN
  DECLARE i INT DEFAULT 0;
  theloop: loop
    SELECT *
    FROM test
    WHERE Description LIKE '%test' COLLATE utf8_general_ci;
    SET i = i + 1;
    IF i = 30 THEN
      LEAVE theloop;
    END IF;
  END LOOP theloop;
END;

CREATE PROCEDURE benchmark_order_by()
BEGIN
  DECLARE i INT DEFAULT 0;
  theloop: loop
    SELECT *
    FROM test
    WHERE ID > FLOOR(1 + RAND() * (400000 - 1))
    ORDER BY Description COLLATE utf8_general_ci LIMIT 1000;
    SET i = i + 1;
    IF i = 10 THEN
      LEAVE theloop;
    END IF;
  END LOOP theloop;
END;

在上面的存储过程中使用了utf8_general_ci排序，但当然，在测试期间，我同时使用了utf8_general_ci和utf8_unicode_ci。

对于每种排序，我调用每个存储过程5次(utf8_general_ci调用5次，utf8_unicode_ci调用5次)，然后计算平均值。

我的结果是:

benchmark_simple_select ()

utf8_general_ci: 9,957 ms utf8_unicode_ci: 10,271 ms

在这个基准测试中，使用utf8_unicode_ci比使用utf8_general_ci慢3.2%。

benchmark_select_like ()

使用utf8_general_ci: 11,441 ms 使用utf8_unicode_ci: 12,811 ms

在这个基准测试中，使用utf8_unicode_ci比使用utf8_general_ci慢12%。

benchmark_order_by ()

使用utf8_general_ci: 11,944 ms 使用utf8_unicode_ci: 12,887 ms

在这个基准测试中，使用utf8_unicode_ci比使用utf8_general_ci慢7.9%。

简单来说:

如果您需要更好的排序顺序-使用utf8_unicode_ci(这是首选方法)，

但是如果您对性能非常感兴趣，可以使用utf8_general_ci，但要知道它有点过时了。

性能方面的差异非常微小。

请参阅mysql手册，Unicode字符集部分:

For any Unicode character set, operations performed using the _general_ci collation are faster than those for the _unicode_ci collation. For example, comparisons for the utf8_general_ci collation are faster, but slightly less correct, than comparisons for utf8_unicode_ci. The reason for this is that utf8_unicode_ci supports mappings such as expansions; that is, when one character compares as equal to combinations of other characters. For example, in German and some other languages “ß” is equal to “ss”. utf8_unicode_ci also supports contractions and ignorable characters. utf8_general_ci is a legacy collation that does not support expansions, contractions, or ignorable characters. It can make only one-to-one comparisons between characters.

因此，总的来说，utf_general_ci使用的比较集比utf_unicode_ci更小，更不正确(根据标准)，后者应该实现整个标准。general_ci集将更快，因为要做的计算更少。

根据这篇文章，在MySQL 5.7上使用utf8mb4_general_ci而不是utf8mb4_unicode_ci有相当大的性能优势: https://www.percona.com/blog/2019/02/27/charset-and-collation-settings-impact-on-mysql-performance/