mysql字符集問題utf8mb4

本文轉載自查看原文 2018-12-04 17:48 898 DB

MySQL默認的字符編碼為utf8，修改為utf8mb4后可支持emoji表情。

utf8mb4解決了MySQL數據庫存儲emoji表情的問題。utf8mb4是utf8的超集，理論上由utf8升級到utf8mb4字符編碼沒有任何兼容問題。

升級utf8到utf8mb4前先備份

1、備份所有需要升級的數據庫，如果是虛機最好做快照。

2、查看mysql版本是否高於5.5.3。

3、查看當前系統默認的字符集設置

mysql> SHOW VARIABLES WHERE Variable_name LIKE 'character\_set\_%' OR Variable_name LIKE 'collation%';
+--------------------------+-----------------+
| Variable_name            | Value           |
+--------------------------+-----------------+
| character_set_client     | utf8            |
| character_set_connection | utf8            |
| character_set_database   | utf8            |
| character_set_filesystem | binary          |
| character_set_results    | utf8            |
| character_set_server     | utf8            |
| character_set_system     | utf8            |
| collation_connection     | utf8_general_ci |
| collation_database       | utf8_general_ci |
| collation_server         | utf8_general_ci |
+--------------------------+-----------------+
10 rows in set (0.01 sec)

mysql>

4、查看database的字符編碼

#polarsnow 為庫名；

mysql> show create database polarsnow;
+-----------+--------------------------------------------------------------------+
| Database  | Create Database                                                    |
+-----------+--------------------------------------------------------------------+
| polarsnow | CREATE DATABASE `polarsnow` /*!40100 DEFAULT CHARACTER SET utf8 */ |
+-----------+--------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql>

5、查看table的字符編碼

mysql> show create table ps;
+-------+---------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                |
+-------+---------------------------------------------------------------------------------------------+
| ps    | CREATE TABLE `ps` (
  `name` varchar(100) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+---------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

6、查看column的字符編碼

mysql> show full columns from ps;
+-------+--------------+-----------------+------+-----+---------+-------+---------------------------------+---------+
| Field | Type         | Collation       | Null | Key | Default | Extra | Privileges                      | Comment |
+-------+--------------+-----------------+------+-----+---------+-------+---------------------------------+---------+
| name  | varchar(100) | utf8_general_ci | YES  |     | NULL    |       | select,insert,update,references |         |
+-------+--------------+-----------------+------+-----+---------+-------+---------------------------------+---------+
1 row in set (0.00 sec)

修改：

修改database默認的字符集：

ALTER DATABASE database_name CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci;

mysql> ALTER DATABASE polarsnow CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci;
Query OK, 1 row affected (0.03 sec)

mysql> show create database polarsnow;
+-----------+--------------------------------------------------------------------------------------------------+
| Database  | Create Database                                                                                  |
+-----------+--------------------------------------------------------------------------------------------------+
| polarsnow | CREATE DATABASE `polarsnow` /*!40100 DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci */ |
+-----------+--------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> show tables;
+---------------------+
| Tables_in_polarsnow |
+---------------------+
| ps                  |
+---------------------+
1 row in set (0.00 sec)

mysql> show create table ps;
+-------+---------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                |
+-------+---------------------------------------------------------------------------------------------+
| ps    | CREATE TABLE `ps` (
  `name` varchar(100) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+---------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> show full columns from ps;
+-------+--------------+-----------------+------+-----+---------+-------+---------------------------------+---------+
| Field | Type         | Collation       | Null | Key | Default | Extra | Privileges                      | Comment |
+-------+--------------+-----------------+------+-----+---------+-------+---------------------------------+---------+
| name  | varchar(100) | utf8_general_ci | YES  |     | NULL    |       | select,insert,update,references |         |
+-------+--------------+-----------------+------+-----+---------+-------+---------------------------------+---------+
1 row in set (0.00 sec)

mysql> create table test_tb2 (tb2 varchar(100) );
Query OK, 0 rows affected (0.21 sec)

mysql> show tables;
+---------------------+
| Tables_in_polarsnow |
+---------------------+
| ps                  |
| test_tb2            |
+---------------------+
2 rows in set (0.00 sec)

mysql> show create table test_tb2;
+----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table    | Create Table                                                                                                                                              |
+----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------+
| test_tb2 | CREATE TABLE `test_tb2` (
  `tb2` varchar(100) COLLATE utf8mb4_unicode_ci DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci |
+----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql>

修改table的字符集

1、只修改表默認的字符集：

ALTER TABLE table_name DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;

2、修改表默認的字符集和所有字符列的字符集：

ALTER TABLE table_name CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;

mysql> show create table ps;
+-------+---------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                |
+-------+---------------------------------------------------------------------------------------------+
| ps    | CREATE TABLE `ps` (
  `name` varchar(100) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+---------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> show full columns from ps;
+-------+--------------+-----------------+------+-----+---------+-------+---------------------------------+---------+
| Field | Type         | Collation       | Null | Key | Default | Extra | Privileges                      | Comment |
+-------+--------------+-----------------+------+-----+---------+-------+---------------------------------+---------+
| name  | varchar(100) | utf8_general_ci | YES  |     | NULL    |       | select,insert,update,references |         |
+-------+--------------+-----------------+------+-----+---------+-------+---------------------------------+---------+
1 row in set (0.00 sec)

mysql> ALTER TABLE ps CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
Query OK, 0 rows affected (0.38 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show create table ps;
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                         |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------+
| ps    | CREATE TABLE `ps` (
  `name` varchar(100) COLLATE utf8mb4_unicode_ci DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> show full columns from ps;
+-------+--------------+--------------------+------+-----+---------+-------+---------------------------------+---------+
| Field | Type         | Collation          | Null | Key | Default | Extra | Privileges                      | Comment |
+-------+--------------+--------------------+------+-----+---------+-------+---------------------------------+---------+
| name  | varchar(100) | utf8mb4_unicode_ci | YES  |     | NULL    |       | select,insert,update,references |         |
+-------+--------------+--------------------+------+-----+---------+-------+---------------------------------+---------+
1 row in set (0.00 sec)

mysql>

3、修改column默認的字符集

ALTER TABLE table_name CHANGE column_name column_name VARCHAR(191) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;

檢查字段的最大長度和索引列

字段長度

由於從utf8升級到了utf8mb4，一個字符所占用的空間也由3個字節增長到4個字節，但是我們當初創建表時，設置的字段類型以及最大的長度沒有改變。例如，你在utf8下設置某一字段的類型為TINYTEXT, 這中字段類型最大可以容納255字節，三個字節一個字符的情況下可以容納85個字符，四個字節一個字符的情況下只能容納63個字符，如果原表中的這個字段的值有一個或多個超過了63個字符，那么轉換成utf8mb4字符編碼時將轉換失敗，你必須先將TINYTEXT更改為TEXT等更高容量的類型之后才能繼續轉換字符編碼

索引

在InnoDB引擎中，最大的索引長度為767字節，三個字節一個字符的情況下，索引列的字符長度最大可以達到255，四個字節一個字符的情況下，索引的字符長度最大只能到191。如果你已經存在的表中的索引列的類型為VARCHAR(255)那么轉換utf8mb4時同樣會轉換失敗。你需要先將VARCHAR(255)更改為VARCHAR(191)才能繼續轉換字符編碼

修改配置文件

修改 vim /etc/my.cnf
# 對本地的mysql客戶端的配置
[client]
default-character-set = utf8mb4

# 對其他遠程連接的mysql客戶端的配置
[mysql]
default-character-set = utf8mb4

# 本地mysql服務的配置
[mysqld]
character-set-client-handshake = FALSE
character-set-server = utf8mb4
collation-server = utf8mb4_unicode_ci
> service mysqld restart

View Code

檢查修改：

mysql> SHOW VARIABLES WHERE Variable_name LIKE 'character\_set\_%' OR Variable_name LIKE 'collation%';
+--------------------------+--------------------+
| Variable_name            | Value              |
+--------------------------+--------------------+
| character_set_client     | utf8mb4            |
| character_set_connection | utf8mb4            |
| character_set_database   | utf8mb4            |
| character_set_filesystem | binary             |
| character_set_results    | utf8mb4            |
| character_set_server     | utf8mb4            |
| character_set_system     | utf8               |
| collation_connection     | utf8mb4_unicode_ci |
| collation_database       | utf8mb4_unicode_ci |
| collation_server         | utf8mb4_unicode_ci |
+--------------------------+--------------------+
10 rows in set (0.00 sec)

View Code

修復&優化所有數據表

> mysqlcheck -u root -p --auto-repair --optimize --all-databases

參考文檔：

https://docs.lvrui.io/2016/08/21/%E4%BF%AE%E6%94%B9MySQL%E7%9A%84%E5%AD%97%E7%AC%A6%E9%9B%86%E4%B8%BAutf8mb4/

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