Mysql alter database character set

from utf8 to utf8mb4:

1.show all DATABASE default characterset:

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

2.show all tables status(character set), focus on column 'collation':

use YOUR_DATABASE_NAME;    
SHOW TABLE STATUS ;

3.generate convert sql: convert database & all tables to 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.run the sql generated.

5.refresh your database.

6.check:

SHOW TABLE STATUS ;

13.1.1 ALTER DATABASE Statement

ALTER {DATABASE | SCHEMA} [db_name]
    alter_option ...
ALTER {DATABASE | SCHEMA} db_name
    UPGRADE DATA DIRECTORY NAME

alter_option: {
    [DEFAULT] CHARACTER SET [=] charset_name
  | [DEFAULT] COLLATE [=] collation_name
}

ALTER DATABASE enables you to change the overall characteristics of a database. These characteristics are stored in the db.opt file in the database directory. This statement requires the ALTER privilege on the database. ALTER SCHEMA is a synonym for ALTER DATABASE.

The database name can be omitted from the first syntax, in which case the statement applies to the default database. An error occurs if there is no default database.

• Character Set and Collation Options

• Upgrading from Versions Older than MySQL 5.1

Character Set and Collation Options

The CHARACTER SET clause changes the default database character set. The COLLATE clause changes the default database collation. For information about character set and collation names, see Chapter 10, Character Sets, Collations, Unicode.

To see the available character sets and collations, use the SHOW CHARACTER SET and SHOW COLLATION statements, respectively. See Section 13.7.5.3, “SHOW CHARACTER SET Statement”, and Section 13.7.5.4, “SHOW COLLATION Statement”.

A stored routine that uses the database defaults when the routine is created includes those defaults as part of its definition. (In a stored routine, variables with character data types use the database defaults if the character set or collation are not specified explicitly. See Section 13.1.16, “CREATE PROCEDURE and CREATE FUNCTION Statements”.) If you change the default character set or collation for a database, any stored routines that are to use the new defaults must be dropped and recreated.

Upgrading from Versions Older than MySQL 5.1

The syntax that includes the UPGRADE DATA DIRECTORY NAME clause updates the name of the directory associated with the database to use the encoding implemented in MySQL 5.1 for mapping database names to database directory names (see Section 9.2.4, “Mapping of Identifiers to File Names”). This clause is for use under these conditions:

• It is intended when upgrading MySQL to 5.1 or later from older versions.

• It is intended to update a database directory name to the current encoding format if the name contains special characters that need encoding.

• The statement is used by mysqlcheck (as invoked by mysql_upgrade).

For example, if a database in MySQL 5.0 has the name a-b-c, the name contains instances of the - (dash) character. In MySQL 5.0, the database directory is also named a-b-c, which is not necessarily safe for all file systems. In MySQL 5.1 and later, the same database name is encoded as a@002db@002dc to produce a file system-neutral directory name.

When a MySQL installation is upgraded to MySQL 5.1 or later from an older version,the server displays a name such as a-b-c (which is in the old format) as #mysql50#a-b-c, and you must refer to the name using the #mysql50# prefix. Use UPGRADE DATA DIRECTORY NAME in this case to explicitly tell the server to re-encode the database directory name to the current encoding format:

ALTER DATABASE `#mysql50#a-b-c` UPGRADE DATA DIRECTORY NAME;

After executing this statement, you can refer to the database as a-b-c without the special #mysql50# prefix.

Note

The UPGRADE DATA DIRECTORY NAME clause is deprecated in MySQL 5.7 and removed in MySQL 8.0. If it is necessary to convert MySQL 5.0 database or table names, a workaround is to upgrade a MySQL 5.0 installation to MySQL 5.1 before upgrading to MySQL 8.0.

How do I change the character set of a database?

How do I change utf8mb4 to utf8?

What is MySQL character set?

Is UTF