MySQL collate的选择
前言
版本说明
mysql=8.0.17
相关链接：
- https://dev.mysql.com/doc/refman/8.0/en/charset-unicode-sets.html
_general_ci 与 _unicode_ci 归类
对于任何Unicode字符集，使用xxx_general_ci 归类执行的操作都比 xxx_unicode_ci 归类中的操作要快。例如， utf8_general_ci归类的比较比的比较更快，但正确性稍差 utf8_unicode_ci。原因是 utf8_unicode_ci支持扩展等映射。
collate 比较
SELECT * FROM INFORMATION_SCHEMA.COLLATIONS WHERE CHARACTER_SET_NAME = 'utf8mb4';
| COLLATION_NAME | CHARACTER_SET_NAME | ID | IS_DEFAULT | IS_COMPILED | SORTLEN | PAD_ATTRIBUTE |
|---|---|---|---|---|---|---|
| utf8mb4_general_ci | utf8mb4 | 45 | Yes | 1 | PAD SPACE | |
| utf8mb4_bin | utf8mb4 | 46 | Yes | 1 | PAD SPACE | |
| utf8mb4_unicode_ci | utf8mb4 | 224 | Yes | 8 | PAD SPACE | |
| utf8mb4_icelandic_ci | utf8mb4 | 225 | Yes | 8 | PAD SPACE | |
| utf8mb4_latvian_ci | utf8mb4 | 226 | Yes | 8 | PAD SPACE | |
| utf8mb4_romanian_ci | utf8mb4 | 227 | Yes | 8 | PAD SPACE | |
| utf8mb4_slovenian_ci | utf8mb4 | 228 | Yes | 8 | PAD SPACE | |
| utf8mb4_polish_ci | utf8mb4 | 229 | Yes | 8 | PAD SPACE | |
| utf8mb4_estonian_ci | utf8mb4 | 230 | Yes | 8 | PAD SPACE | |
| utf8mb4_spanish_ci | utf8mb4 | 231 | Yes | 8 | PAD SPACE | |
| utf8mb4_swedish_ci | utf8mb4 | 232 | Yes | 8 | PAD SPACE | |
| utf8mb4_turkish_ci | utf8mb4 | 233 | Yes | 8 | PAD SPACE | |
| utf8mb4_czech_ci | utf8mb4 | 234 | Yes | 8 | PAD SPACE | |
| utf8mb4_danish_ci | utf8mb4 | 235 | Yes | 8 | PAD SPACE | |
| utf8mb4_lithuanian_ci | utf8mb4 | 236 | Yes | 8 | PAD SPACE | |
| utf8mb4_slovak_ci | utf8mb4 | 237 | Yes | 8 | PAD SPACE | |
| utf8mb4_spanish2_ci | utf8mb4 | 238 | Yes | 8 | PAD SPACE | |
| utf8mb4_roman_ci | utf8mb4 | 239 | Yes | 8 | PAD SPACE | |
| utf8mb4_persian_ci | utf8mb4 | 240 | Yes | 8 | PAD SPACE | |
| utf8mb4_esperanto_ci | utf8mb4 | 241 | Yes | 8 | PAD SPACE | |
| utf8mb4_hungarian_ci | utf8mb4 | 242 | Yes | 8 | PAD SPACE | |
| utf8mb4_sinhala_ci | utf8mb4 | 243 | Yes | 8 | PAD SPACE | |
| utf8mb4_german2_ci | utf8mb4 | 244 | Yes | 8 | PAD SPACE | |
| utf8mb4_croatian_ci | utf8mb4 | 245 | Yes | 8 | PAD SPACE | |
| utf8mb4_unicode_520_ci | utf8mb4 | 246 | Yes | 8 | PAD SPACE | |
| utf8mb4_vietnamese_ci | utf8mb4 | 247 | Yes | 8 | PAD SPACE | |
| utf8mb4_0900_ai_ci | utf8mb4 | 255 | Yes | Yes | 0 | NO PAD |
| utf8mb4_de_pb_0900_ai_ci | utf8mb4 | 256 | Yes | 0 | NO PAD | |
| utf8mb4_is_0900_ai_ci | utf8mb4 | 257 | Yes | 0 | NO PAD | |
| utf8mb4_lv_0900_ai_ci | utf8mb4 | 258 | Yes | 0 | NO PAD | |
| utf8mb4_ro_0900_ai_ci | utf8mb4 | 259 | Yes | 0 | NO PAD | |
| utf8mb4_sl_0900_ai_ci | utf8mb4 | 260 | Yes | 0 | NO PAD | |
| utf8mb4_pl_0900_ai_ci | utf8mb4 | 261 | Yes | 0 | NO PAD | |
| utf8mb4_et_0900_ai_ci | utf8mb4 | 262 | Yes | 0 | NO PAD | |
| utf8mb4_es_0900_ai_ci | utf8mb4 | 263 | Yes | 0 | NO PAD | |
| utf8mb4_sv_0900_ai_ci | utf8mb4 | 264 | Yes | 0 | NO PAD | |
| utf8mb4_tr_0900_ai_ci | utf8mb4 | 265 | Yes | 0 | NO PAD | |
| utf8mb4_cs_0900_ai_ci | utf8mb4 | 266 | Yes | 0 | NO PAD | |
| utf8mb4_da_0900_ai_ci | utf8mb4 | 267 | Yes | 0 | NO PAD | |
| utf8mb4_lt_0900_ai_ci | utf8mb4 | 268 | Yes | 0 | NO PAD | |
| utf8mb4_sk_0900_ai_ci | utf8mb4 | 269 | Yes | 0 | NO PAD | |
| utf8mb4_es_trad_0900_ai_ci | utf8mb4 | 270 | Yes | 0 | NO PAD | |
| utf8mb4_la_0900_ai_ci | utf8mb4 | 271 | Yes | 0 | NO PAD | |
| utf8mb4_eo_0900_ai_ci | utf8mb4 | 273 | Yes | 0 | NO PAD | |
| utf8mb4_hu_0900_ai_ci | utf8mb4 | 274 | Yes | 0 | NO PAD | |
| utf8mb4_hr_0900_ai_ci | utf8mb4 | 275 | Yes | 0 | NO PAD | |
| utf8mb4_vi_0900_ai_ci | utf8mb4 | 277 | Yes | 0 | NO PAD | |
| utf8mb4_0900_as_cs | utf8mb4 | 278 | Yes | 0 | NO PAD | |
| utf8mb4_de_pb_0900_as_cs | utf8mb4 | 279 | Yes | 0 | NO PAD | |
| utf8mb4_is_0900_as_cs | utf8mb4 | 280 | Yes | 0 | NO PAD | |
| utf8mb4_lv_0900_as_cs | utf8mb4 | 281 | Yes | 0 | NO PAD | |
| utf8mb4_ro_0900_as_cs | utf8mb4 | 282 | Yes | 0 | NO PAD | |
| utf8mb4_sl_0900_as_cs | utf8mb4 | 283 | Yes | 0 | NO PAD | |
| utf8mb4_pl_0900_as_cs | utf8mb4 | 284 | Yes | 0 | NO PAD | |
| utf8mb4_et_0900_as_cs | utf8mb4 | 285 | Yes | 0 | NO PAD | |
| utf8mb4_es_0900_as_cs | utf8mb4 | 286 | Yes | 0 | NO PAD | |
| utf8mb4_sv_0900_as_cs | utf8mb4 | 287 | Yes | 0 | NO PAD | |
| utf8mb4_tr_0900_as_cs | utf8mb4 | 288 | Yes | 0 | NO PAD | |
| utf8mb4_cs_0900_as_cs | utf8mb4 | 289 | Yes | 0 | NO PAD | |
| utf8mb4_da_0900_as_cs | utf8mb4 | 290 | Yes | 0 | NO PAD | |
| utf8mb4_lt_0900_as_cs | utf8mb4 | 291 | Yes | 0 | NO PAD | |
| utf8mb4_sk_0900_as_cs | utf8mb4 | 292 | Yes | 0 | NO PAD | |
| utf8mb4_es_trad_0900_as_cs | utf8mb4 | 293 | Yes | 0 | NO PAD | |
| utf8mb4_la_0900_as_cs | utf8mb4 | 294 | Yes | 0 | NO PAD | |
| utf8mb4_eo_0900_as_cs | utf8mb4 | 296 | Yes | 0 | NO PAD | |
| utf8mb4_hu_0900_as_cs | utf8mb4 | 297 | Yes | 0 | NO PAD | |
| utf8mb4_hr_0900_as_cs | utf8mb4 | 298 | Yes | 0 | NO PAD | |
| utf8mb4_vi_0900_as_cs | utf8mb4 | 300 | Yes | 0 | NO PAD | |
| utf8mb4_ja_0900_as_cs | utf8mb4 | 303 | Yes | 0 | NO PAD | |
| utf8mb4_ja_0900_as_cs_ks | utf8mb4 | 304 | Yes | 24 | NO PAD | |
| utf8mb4_0900_as_ci | utf8mb4 | 305 | Yes | 0 | NO PAD | |
| utf8mb4_ru_0900_ai_ci | utf8mb4 | 306 | Yes | 0 | NO PAD | |
| utf8mb4_ru_0900_as_cs | utf8mb4 | 307 | Yes | 0 | NO PAD | |
| utf8mb4_zh_0900_as_cs | utf8mb4 | 308 | Yes | 0 | NO PAD | |
| utf8mb4_0900_bin | utf8mb4 | 309 | Yes | 1 | NO PAD |
数据库表结构及数据
create database db_test character set utf8mb4;
use db_test;
create table if not exists `t_test`(
`id` int primary key auto_increment,
`no_pad` varchar(20) character set utf8mb4 collate utf8mb4_0900_bin,
`pad` varchar(20) character set utf8mb4 collate utf8mb4_bin
)engine =innodb;
insert into t_test(`no_pad`, `pad`) values ('a', 'b ');
insert into t_test(`no_pad`, `pad`) values ('a ', 'b ');
insert into t_test(`no_pad`, `pad`) values ('a', 'b');
insert into t_test(`no_pad`, `pad`) values ('a ', 'b');
PAD_ATTRIBUTE 比较
- NO PAD ：
'a'和'a '是不相等的 - PAD SPACE ：
'a'和'a '是相等的
