Using this example, you can change character set and collation for a MySQL database table(s).
Most likely you will be need to do this if you haven’t specified character set and collation at the time of database/table creation and default character set/collation applied are not desirable.
Setting MySQL default character set and collation in my.cnf
Below are settings for MySQL version 5.5.9 and onwards.
Put them in /etc/mysql/my.cnf is correct sections. Please be careful as some settings might be already present.
[mysqld] character-set-server=utf8 collation-server = utf8_unicode_ci init-connect='SET NAMES utf8' init_connect='SET collation_connection = utf8_unicode_ci' skip-character-set-client-handshake
Next, restart mysql and log into mysql shell:
mysql> show variables like "%character%";show variables like "%collation%";
Sample output as:
+--------------------------+----------------------------+ | 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 | | character_sets_dir | /usr/share/mysql/charsets/ | +--------------------------+----------------------------+ 8 rows in set (0.00 sec) +----------------------+-----------------+ | Variable_name | Value | +----------------------+-----------------+ | collation_connection | utf8_general_ci | | collation_database | utf8_general_ci | | collation_server | utf8_general_ci | +----------------------+-----------------+ 3 rows in set (0.00 sec)
Checking current character set and collation for database/table/columns
For Database:
SELECT default_character_set_name, default_collation_name FROM information_schema.SCHEMATA WHERE schema_name = "databasename";
It will show output as:
+----------------------------+------------------------+ | default_character_set_name | default_collation_name | +----------------------------+------------------------+ | latin1 | latin1_swedish_ci | +----------------------------+------------------------+
For Tables:
SELECT T.table_name, T.table_collation, CCSA.character_set_name FROM information_schema.`TABLES` T, information_schema.`COLLATION_CHARACTER_SET_APPLICABILITY` CCSA WHERE CCSA.collation_name = T.table_collation AND T.table_schema = "databasename";
Sample output as below:
+-----------------------------------------------------+-------------------+--------------------+ | table_name | table_collation | character_set_name | +-----------------------------------------------------+-------------------+--------------------+ | wp_20_rtAccountToken | latin1_swedish_ci | latin1 | | wp_20_rtAccountVerify | latin1_swedish_ci | latin1 | | wp_20_rt_crm_mail_messageids | latin1_swedish_ci | latin1 | | wp_20_w3tc_cdn_queue | latin1_swedish_ci | latin1 | | gp_meta | utf8_general_ci | utf8 | +-----------------------------------------------------+-------------------+--------------------+
For Columns:
SELECT table_name, column_name, character_set_name, collation_name FROM information_schema.`COLUMNS` C WHERE character_set_name != 'NULL' AND table_schema = "db_name"
Sample Output:
+------------------------+--------------+--------------------+-------------------+ | table_name | column_name | character_set_name | collation_name | +------------------------+--------------+--------------------+-------------------+ | wp_20_rtAccountToken | accesstoken | latin1 | latin1_swedish_ci | | wp_20_rtAccountToken | refreshtoken | latin1 | latin1_swedish_ci | | wp_20_rtAccountVerify | email | latin1 | latin1_swedish_ci | | wp_20_rtAccountVerify | type | latin1 | latin1_swedish_ci | | wp_20_rtAccountVerify | code | latin1 | latin1_swedish_ci | +------------------------+--------------+--------------------+-------------------+
Converting character set and collations
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Changing Database Character Sets and Collations
This is simplest:
ALTER DATABASE db_name CHARACTER SET utf8 COLLATE utf8_general_ci;
Replace your database name with db_name. Also after running query verify if database-level defaults are changed indeed.
Changing Tables Character Sets and Collations
Below is a syntax to covert character set ofwp_posts and wp_postmetatables.
alter table wp_posts convert to character set utf8 collate utf8_unicode_ci; alter table wp_postmeta convert to character set utf8 collate utf8_unicode_ci;
If you want to covert all your MySQL tables, then run a command like below on database db_wordpress
mysql -e "SELECT concat('alter table ', TABLE_NAME , ' convert to character set utf8 collate utf8_unicode_ci;')
FROM information_schema.TABLES
WHERE table_schema = 'db_wordpress'
AND TABLE_COLLATION = 'latin1_swedish_ci'" |
tail -n+2 > collation.sql
After you run above query, check collation.sql content to verify if all rows are correct. If collation.sql is empty, you probably do not have a table using MyISAM engine.
If all looks good, run following to convert all mysql tables to InnoDB.
mysql db_wordpress < collation.sql
Changing Column Character Sets and Collations
Below is syntax to convert columns to utf8
alter table table_name change col_name col_name col_data_type character set utf8;
Please note that we have to use same col_name twice!
col_data_type can be found form a sql query like…
mysql> SELECT table_name, column_name, data_type, character_set_name, collation_name FROM information_schema.`COLUMNS` WHERE table_schema = "db_name" AND table_name = "table_name" AND column_name = "col_name";
Sample output:
+--------------+--------------+-----------+ | table_name | column_name | data_type | +--------------+--------------+-----------+ | wp_posts | post_content | longtext | +--------------+--------------+-----------+
Example for wordpress’s wp_posts table
alter table wp_posts change post_content post_content LONGTEXT CHARACTER SET utf8;
Please be very careful for column conversion. Specially if you have non-english characters stored in database. In that case, you can refer to this WordPress Codex section.