最安全的方法是先将列修改为二进制类型，然后使用所需的字符集将其修改回二进制类型。

每种列类型都有其各自的二进制类型，如下所示:

>二进制 文本=> BLOB 丁文字=> TINYBLOB 文本=> memblob LONGTEXT => LONGBLOB VARCHAR => VARBINARY

Eg.:

ALTER TABLE [TABLE_SCHEMA].[TABLE_NAME] MODIFY [COLUMN_NAME] VARBINARY;

ALTER TABLE [TABLE_SCHEMA].[TABLE_NAME] MODIFY [COLUMN_NAME] VARCHAR(140) CHARACTER SET utf8mb4;

我尝试了几个拉丁表，它保留了所有的变音符。

你可以为所有列提取这个查询:

SELECT
CONCAT('ALTER TABLE ', TABLE_SCHEMA,'.', TABLE_NAME,' MODIFY ', COLUMN_NAME,' VARBINARY;'),
CONCAT('ALTER TABLE ', TABLE_SCHEMA,'.', TABLE_NAME,' MODIFY ', COLUMN_NAME,' ', COLUMN_TYPE,' CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci;')
FROM information_schema.columns
WHERE TABLE_SCHEMA IN ('[TABLE_SCHEMA]')
AND COLUMN_TYPE LIKE 'varchar%'
AND (COLLATION_NAME IS NOT NULL AND COLLATION_NAME NOT LIKE 'utf%');

在所有列上执行此操作后，再对所有表执行此操作:

ALTER TABLE [TABLE_SCHEMA].[TABLE_NAME] CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci;

要为你所有的表生成这个查询，使用下面的查询:

SELECT
CONCAT('ALTER TABLE ', TABLE_SCHEMA, '.', TABLE_NAME, ' CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci;')
FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_COLLATION NOT LIKE 'utf8%'
and TABLE_SCHEMA in ('[TABLE_SCHEMA]');

现在你修改了所有的列和表，在数据库上做同样的事情:

ALTER DATABASE [DATA_BASE_NAME] CHARSET = utf8mb4 COLLATE = utf8mb4_general_ci;

在命令行shell上

如果你是一个命令行shell，你可以非常快地做到这一点。只需填写“dbname”:D

DB="dbname"
(
    echo 'ALTER DATABASE `'"$DB"'` CHARACTER SET utf8 COLLATE utf8_general_ci;'
    mysql "$DB" -e "SHOW TABLES" --batch --skip-column-names \
    | xargs -I{} echo 'ALTER TABLE `'{}'` CONVERT TO CHARACTER SET utf8 COLLATE utf8_general_ci;'
) \
| mysql "$DB"

简单复制/粘贴的一行程序

DB="dbname"; ( echo 'ALTER DATABASE `'"$DB"'` CHARACTER SET utf8 COLLATE utf8_general_ci;'; mysql "$DB" -e "SHOW TABLES" --batch --skip-column-names | xargs -I{} echo 'ALTER TABLE `'{}'` CONVERT TO CHARACTER SET utf8 COLLATE utf8_general_ci;' ) | mysql "$DB"

对于有大量表的数据库，你可以使用一个简单的php脚本来更新数据库和所有表的字符集，使用以下方法:

$conn = mysqli_connect($host, $username, $password, $database);

if ($conn->connect_error) {
  die("Connection failed: " . $conn->connect_error);
}

$alter_database_charset_sql = "ALTER DATABASE ".$database." CHARACTER SET utf8 COLLATE utf8_unicode_ci";
mysqli_query($conn, $alter_database_charset_sql);

$show_tables_result = mysqli_query($conn, "SHOW TABLES");
$tables  = mysqli_fetch_all($show_tables_result);

foreach ($tables as $index => $table) {
  $alter_table_sql = "ALTER TABLE ".$table[0]." CONVERT TO CHARACTER SET utf8  COLLATE utf8_unicode_ci";
  $alter_table_result = mysqli_query($conn, $alter_table_sql);
  echo "<pre>";
  var_dump($alter_table_result);
  echo "</pre>";
}

utf8到utf8mb4:

1.显示所有数据库默认字符集:

SELECT SCHEMA_NAME 'YOUR_DATABASE_NAME', 
default_character_set_name 'charset', 
DEFAULT_COLLATION_NAME 'collation' 
FROM information_schema.SCHEMATA;

2.显示所有表的状态(字符集)，关注列的“collation”:

use YOUR_DATABASE_NAME;    
SHOW TABLE STATUS ;

3.生成转换sql: 转换数据库和所有表utf8mb4,utf8mb4_unicode_ci

USE information_schema;
SELECT CONCAT("ALTER DATABASE `",table_schema,"` CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci;") AS _sql
FROM `TABLES` WHERE table_schema LIKE "YOUR_DATABASE_NAME" AND TABLE_TYPE='BASE TABLE' GROUP BY table_schema UNION
SELECT CONCAT("ALTER TABLE `",table_schema,"`.`",table_name,"` CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;") AS _sql  
FROM `TABLES` WHERE table_schema LIKE "YOUR_DATABASE_NAME" AND TABLE_TYPE='BASE TABLE' GROUP BY table_schema, TABLE_NAME 
/*include all columns, commonly don't need this.*/
/*
UNION
SELECT CONCAT("ALTER TABLE `",`COLUMNS`.table_schema,"`.`",`COLUMNS`.table_name, "` CHANGE `",column_name,"` `",column_name,"` ",data_type,"(",character_maximum_length,") CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci",IF(is_nullable="YES"," NULL"," NOT NULL"),";") AS _sql 
FROM `COLUMNS` INNER JOIN `TABLES` ON `TABLES`.table_name = `COLUMNS`.table_name WHERE `COLUMNS`.table_schema like "YOUR_DATABASE_NAME" and data_type in ('varchar','char') AND TABLE_TYPE='BASE TABLE' UNION
SELECT CONCAT("ALTER TABLE `",`COLUMNS`.table_schema,"`.`",`COLUMNS`.table_name, "` CHANGE `",column_name,"` `",column_name,"` ",data_type," CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci",IF(is_nullable="YES"," NULL"," NOT NULL"),";") AS _sql 
FROM `COLUMNS` INNER JOIN `TABLES` ON `TABLES`.table_name = `COLUMNS`.table_name WHERE `COLUMNS`.table_schema like "YOUR_DATABASE_NAME" and data_type in ('text','tinytext','mediumtext','longtext') AND TABLE_TYPE='BASE TABLE';
*/

4.运行生成的SQL语句。

5.刷新数据库。

6.检查:

SHOW TABLE STATUS ;

命令行解决方案和排除视图

我只是在为像我和布莱恩这样在我们的数据库中有视图的人完成@Jasny的回答。

如果你有这样的错误:

ERROR 1347 (HY000) at line 17: 'dbname.table_name' is not of type 'BASE TABLE'

这是因为你可能有自己的观点，你需要排除它们。 但是当试图排除它们时，MySQL返回2列而不是1列。

SHOW FULL TABLES WHERE Table_Type = 'BASE TABLE';
-- table_name1  BASE TABLE
-- table_name2  BASE TABLE

因此，我们必须用awk修改Jasny的命令，只提取包含表名的第一列。

DB="dbname"
(
    echo 'ALTER DATABASE `'"$DB"'` CHARACTER SET utf8 COLLATE utf8_general_ci;'
    mysql "$DB" -e "SHOW FULL TABLES WHERE Table_Type = 'BASE TABLE'" --batch --skip-column-names \
    | awk '{print $1 }' \
    | xargs -I{} echo 'ALTER TABLE `'{}'` CONVERT TO CHARACTER SET utf8 COLLATE utf8_general_ci;'
) \
| mysql "$DB"

简单复制/粘贴的一行程序

DB="dbname"; ( echo 'ALTER DATABASE `'"$DB"'` CHARACTER SET utf8 COLLATE utf8_general_ci;'; mysql "$DB" -e "SHOW FULL TABLES WHERE Table_Type = 'BASE TABLE'" --batch --skip-column-names | awk '{print $1 }' | xargs -I{} echo 'ALTER TABLE `'{}'` CONVERT TO CHARACTER SET utf8 COLLATE utf8_general_ci;' ) | mysql "$DB"

你可以创建sql来更新所有的表:

SELECT CONCAT("ALTER TABLE ",TABLE_SCHEMA,".",TABLE_NAME," CHARACTER SET utf8 COLLATE utf8_general_ci;   ",
    "ALTER TABLE ",TABLE_SCHEMA,".",TABLE_NAME," CONVERT TO CHARACTER SET utf8 COLLATE utf8_general_ci;  ") 
    AS alter_sql
FROM information_schema.TABLES
WHERE TABLE_SCHEMA = "your_database_name";

捕获输出并运行它。

阿诺德•丹尼尔斯(Arnold Daniels)的回答更为优雅。