mysql(5.7.17)字符集设置(character_set/collation)

Posted 2021-01-22 数据库技术和故事

0 查看字符集(character_set/collation)
use information_schema;
desc tables;    --一定记住tables表，information_schema中的metadata都可以查到

-- 查看db的默认，DEFAULT_CHARACTER_SET_NAME/DEFAULT_COLLATION_NAME
select * from schemata where schema_name = ‘db_name‘;

-- 查看table的，只有table_collation字段
select * from tables where table_schema = ‘db_name‘ and table_name = ‘table_name‘;

-- 查看column的，CHARACTER_SET_NAME/COLLATION_NAME都要
select * from columns where table_schema = ‘db_name‘ and table_name = ‘table_name‘;
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--查看mysql支持的character_set，Default collation是默认的"大小写敏感"
select * from information_schema.character_sets;   
--就是执行了上面的sql
show charset;
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/*
查看各character set的collation，以gbk为例
gbk_chinese_ci是"大小写不敏感"，ci是case sensitive的缩写
gbk_bin是"大小写敏感"，以二进制(binary)存储
*/
select * from information_schema.collations;
show collation;
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show variables like ‘character_set%‘;   --查看当前环境的character_set
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show variables like ‘collation%‘;   --查看当前的collation
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1 my.ini配置character_set
-- 注意位置，放在[client]和[mysql]都可以，效果相同，以后面的为准。放在[mysqld]下服务不能启动。
default-character-set = utf8

-- 上句设置之后，对应的全局变量改变
character_set_client = utf8
character_set_connection = utf8
character_set_results = utf8

-- 注意位置，放在[mysqld]下
character-set-server = gbk
collation-server = gbk_bin

-- 上句设置之后，对应的全局变量改变
character_set_database = gbk
character_set_server = gbk    --默认的create database db时的character_set，其他的含义待测试，可根据字面单词猜想
collation_database = gbk_bin
collation_server = gbk_bin
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2 数据库的character_set指定/修改
-- 默认db的character_set和@@character_set_server一致，table和db一致，column和table一致
create database db;

-- defalut可有可无，注意gbk的default collation(上面有)是gbk_chinese_ci(大小写不敏感)
-- 即使collation_database/server都是gbk_bin，创建的db默认仍是gbk_chinese_ci，这里专门指定
create datadbase db character set gbk collate gbk_bin;
create datadbase db default character set gbk collate gbk_bin;  --正确
alter datadbase db character set gbk collate gbk_bin;       --正确

alter datadbase db convert to character set gbk collate gbk_bin;    --错误，不支持convert to
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3 table的character_set指定/修改
create table t1(c1 varchar2) character set gbk collate gbk_chinese_ci;
-- 测试
insert into t1 values(‘a‘);
select * from t1 where c1 = ‘A‘;    --返回‘a‘，此时‘a‘=‘A‘

--注意以下两种方法的差别，第1句是只是修改默认
alter table t1 character set gbk collate gbk_bin;   --提示Records: 0

--测试
alter table t1 add c2 varchar(50);
insert into t1 values(‘b‘,‘b‘);
select * from t1 where c1 = ‘A‘;    --返回‘a‘，c1仍然是gbk_chinese_ci
select * from t1 where c2 = ‘B‘;    --返回empty，c2是gbk_bin

--已有字段c1,c2及再添加的默认都是gbk_bin
alter table t1 convert to character set gbk collate gbk_bin;    --提示Records: 1
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4 column的character_set指定/修改
-- 套路相同
alter table add c1 varchar(50) character set gbk collate gbk_bin;
alter table t1 change c1 c1 varchar(50) character set gbk collate gbk_bin;
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作者：苦笔
来源：CSDN
原文：https://blog.csdn.net/u014711094/article/details/78821809
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