Mysql校验规则

本文介绍了MySQL中的校验规则,包括如何查看数据库、表和列的字符集及校验规则。通过`SHOW DATABASES;`、`SHOW CREATE DATABASE <db_name>;`、`SHOW CREATE TABLE <table_name>;`等命令展示了不同级别的字符集配置。同时,通过`SELECT * FROM COLLATIONS ORDER BY 1, 4;`展示了所有校验规则,强调了默认规则和区分大小写的规则(如*_bin、*_cs、*_ci)。最后,通过示例解释了不同校验规则对排序的影响。" 79380520,7330768,QT编程:QDockWidget停靠窗口详解与应用,"['QT', 'GUI开发', 'QMainWindow', '窗口管理']



--校验规则


mysql> show databases ;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| dao                |
| mysql              |
| performance_schema |
| test               |
+--------------------+
5 rows in set (0.00 sec)


mysql> use information_schema ;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A


Database changed


--校验规则名
--字符集名称
--校验规则ID
--是否为默认校验规则
--是否被编译到MYSQL SERVER中
--


mysql> select * from COLLATIONS order by 1 ,4 ;
+--------------------------+--------------------+-----+------------+-------------+---------+
| COLLATION_NAME           | CHARACTER_SET_NAME | ID  | IS_DEFAULT | IS_COMPILED | SORTLEN |
+--------------------------+--------------------+-----+------------+-------------+---------+
| armscii8_bin             | armscii8           |  64 |            | Yes         |       1 |
| armscii8_general_ci      | armscii8           |  32 | Yes        | Yes         |       1 |
| ascii_bin                | ascii              |  65 |            | Yes         |       1 |
| ascii_general_ci         | ascii              |  11 | Yes        | Yes         |       1 |
| big5_bin                 | big5               |  84 |            | Yes         |       1 |
| big5_chinese_ci          | big5               |   1 | Yes        | Yes         |       1 |
| binary                   | binary             |  63 | Yes        | Yes         |       1 |
| cp1250_bin               | cp1250             |  66 |            | Yes         |       1 |
| cp1250_croatian_ci       | cp1250             |  44 |            | Yes         |       1 |
| cp1250_czech_cs          | cp1250             |  34 |            | Yes         |       2 |
| cp1250_general_ci        | cp1250             |  26 | Yes        | Yes         |       1 |
| cp1250_polish_ci         | cp1250             |  99 |            | Yes         |       1 |
| cp1251_bin               | cp1251             |  50 |            | Yes         |       1 |
| cp1251_bulgarian_ci      | cp1251             |  14 |            | Yes         |       1 |
| cp1251_general_ci        | cp1251             |  51 | Yes        | Yes         |       1 |
| cp1251_general_cs        | cp1251             |  52 |            | Yes         |       1 |
| cp1251_ukrainian_ci      | cp1251             |  23 |            | Yes         |       1 |
| cp1256_bin               | cp1256             |  67 |            | Yes         |       1 |
| cp1256_general_ci        | cp1256             |  57 | Yes        | Yes         |       1 |
| cp1257_bin               | cp1257             |  58 |            | Yes         |       1 |
| cp1257_general_ci        | cp1257             |  59 | Yes        | Yes         |       1 |
| cp1257_lithuanian_ci     | cp1257             |  29 |            | Yes         |       1 |
| cp850_bin                | cp850              |  80 |            | Yes         |       1 |
| cp850_general_ci         | cp850              |   4 | Yes        | Yes         |       1 |
| cp852_bin                | cp852              |  81 |            | Yes         |       1 |
| cp852_general_ci         | cp852              |  40 | Yes        | Yes         |       1 |
| cp866_bin                | cp866              |  68 |            | Yes         |       1 |
| cp866_general_ci         | cp866              |  36 | Yes        | Yes         |       1 |
| cp932_bin                | cp932              |  96 |            | Yes         |       1 |
| cp932_japanese_ci        | cp932              |  95 | Yes        | Yes         |       1 |
| dec8_bin                 | dec8               |  69 |            | Yes         |       1 |
| dec8_swedish_ci          | dec8               |   3 | Yes        | Yes         |       1 |
| eucjpms_bin              | eucjpms            |  98 |            | Yes         |       1 |
| eucjpms_japanese_ci      | eucjpms            |  97 | Yes        | Yes         |       1 |
| euckr_bin                | euckr              |  85 |            | Yes         |       1 |
| euckr_korean_ci          | euckr              |  19 | Yes        | Yes         |       1 |
| gb2312_bin               | gb2312             |  86 |            | Yes         |       1 |
| gb2312_chinese_ci        | gb2312             |  24 | Yes        | Yes         |       1 |
| gbk_bin                  | gbk                |  87 |            | Yes         |       1 |
| gbk_chinese_ci           | gbk                |  28 | Yes        | Yes         |       1 |
| geostd8_bin              | geostd8            |  93 |            | Yes         |       1 |
| geostd8_general_ci       | geostd8            |  92 | Yes        | Yes         |       1 |
| greek_bin                | greek              |  70 |            | Yes         |       1 |
| greek_general_ci         | greek              |  25 | Yes        | Yes         |       1 |
| hebrew_bin               | hebrew             |  71 |            | Yes         |       1 |
| hebrew_general_ci        | hebrew             |  16 | Yes        | Yes         |       1 |
| hp8_bin                  | hp8                |  72 |            | Yes         |       1 |
| hp8_english_ci           | hp8                |   6 | Yes        | Yes         |       1 |
| keybcs2_bin              | keybcs2            |  73 |            | Yes         |       1 |
| keybcs2_general_ci       | keybcs2            |  37 | Yes        | Yes         |       1 |
| koi8r_bin                | koi8r              |  74 |            | Yes         |       1 |
| koi8r_general_ci         | koi8r              |   7 | Yes        | Yes         |       1 |
| koi8u_bin                | koi8u              |  75 |            | Yes         |       1 |
| koi8u_general_ci         | koi8u              |  22 | Yes        | Yes         |       1 |
| latin1_bin               | latin1             |  47 |            | Yes         |       1 |
| latin1_danish_ci         | latin1             |  15 |            | Yes         |       1 |
| latin1_general_ci        | latin1             |  48 |            | Yes         |       1 |
| latin1_general_cs        | latin1             |  49 |            | Yes         |       1 |
| latin1_german1_ci        | latin1             |   5 |            | Yes         |       1 |
| latin1_german2_ci        | latin1             |  31 |            | Yes         |       2 |
| latin1_spanish_ci        | latin1             |  94 |            | Yes         |       1 |
| latin1_swedish_ci        | latin1             |   8 | Yes        | Yes         |       1 |
| latin2_bin               | latin2             |  77 |            | Yes         |       1 |
| latin2_croatian_ci       | latin2             |  27 |            | Yes         |       1 |
| latin2_czech_cs          | latin2             |   2 |            | Yes         |       4 |
| latin2_general_ci        | latin2             |   9 | Yes        | Yes         |       1 |
| latin2_hungarian_ci      | latin2             |  21 |            | Yes         |       1 |
| latin5_bin               | latin5             |  78 |            | Yes         |       1 |
| latin5_turkish_ci        | latin5             |  30 | Yes        | Yes         |       1 |
| latin7_bin               | latin7             |  79 |            | Yes         |       1 |
| latin7_estonian_cs       | latin7             |  20 |            | Yes         |       1 |
| latin7_general_ci        | latin7             |  41 | Yes        | Yes         |       1 |
| latin7_general_cs        | latin7             |  42 |            | Yes         |       1 |
| macce_bin                | macce              |  43 |            | Yes         |       1 |
| macce_general_ci         | macce              |  38 | Yes        | Yes         |       1 |
| macroman_bin             | macroman           |  53 |            | Yes         |       1 |
| macroman_general_ci      | macroman           |  39 | Yes        | Yes         |       1 |
| sjis_bin                 | sjis               |  88 |            | Yes         |       1 |
| sjis_japanese_ci         | sjis               |  13 | Yes        | Yes         |       1 |
| swe7_bin                 | swe7               |  82 |            | Yes         |       1 |
| swe7_swedish_ci          | swe7               |  10 | Yes        | Yes         |       1 |
| tis620_bin               | tis620             |  89 |            | Yes         |       1 |
| tis620_thai_ci           | tis620             |  18 | Yes        | Yes         |       4 |
| ucs2_bin                 | ucs2               |  90 |            | Yes         |       1 |
| ucs2_croatian_ci         | ucs2               | 149 |            | Yes         |       8 |
| ucs2_czech_ci            | ucs2               | 138 |            | Yes         |       8 |
| ucs2_danish_ci           | ucs2               | 139 |            | Yes         |       8 |
| ucs2_esperanto_ci        | ucs2               | 145 |            | Yes         |       8 |
| ucs2_estonian_ci         | ucs2               | 134 |            | Yes         |       8 |
| ucs2_general_ci          | ucs2               |  35 | Yes        | Yes         |       1 |
| ucs2_general_mysql500_ci | ucs2               | 159 |            | Yes         |       1 |
| ucs2_german2_ci          | ucs2               | 148 |            | Yes         |       8 |
| ucs2_hungarian_ci        | ucs2               | 146 |            | Yes         |       8 |
| ucs2_icelandic_ci        | ucs2               | 129 |            | Yes         |       8 |
| ucs2_latvian_ci          | ucs2               | 130 |            | Yes         |       8 |
| ucs2_lithuanian_ci       | ucs2               | 140 |            | Yes         |       8 |
| ucs2_persian_ci          | ucs2               | 144 |            | Yes         |       8 |
| ucs2_polish_ci           | ucs2               | 133 |            | Yes         |       8 |
| ucs2_romanian_ci         | ucs2               | 131 |            | Yes         |       8 |
| ucs2_roman_ci            | ucs2               | 143 |            | Yes         |       8 |
| ucs2_sinhala_ci          | ucs2               | 147 |            | Yes         |       8 |
| ucs2_slovak_ci           | ucs2               | 141 |            | Yes         |       8 |
| ucs2_slovenian_ci        | ucs2               | 132 |            | Yes         |       8 |
| ucs2_spanish2_ci         | ucs2               | 142 |            | Yes         |       8 |
| ucs2_spanish_ci          | ucs2               | 135 |            | Yes         |       8 |
| ucs2_swedish_ci          | ucs2               | 136 |            | Yes         |       8 |
| ucs2_turkish_ci          | ucs2               | 137 |            | Yes         |       8 |
| ucs2_unicode_520_ci      | ucs2               | 150 |            | Yes         |       8 |
| ucs2_unicode_ci          | ucs2               | 128 |            | Yes         |       8 |
| ucs2_vietnamese_ci       | ucs2               | 151 |            | Yes         |       8 |
| ujis_bin                 | ujis               |  91 |            | Yes         |       1 |
| ujis_japanese_ci         | ujis               |  12 | Yes        | Yes         |       1 |
| utf16le_bin              | utf16le            |  62 |            | Yes         |       1 |
| utf16le_general_ci       | utf16le            |  56 | Yes        | Yes         |       1 |
| utf16_bin                | utf16              |  55 |            | Yes         |       1 |
| utf16_croatian_ci        | utf16              | 122 |            | Yes         |       8 |
| utf16_czech_ci           | utf16              | 111 |            | Yes         |       8 |
| utf16_danish_ci          | utf16              | 112 |            | Yes         |       8 |
| utf16_esperanto_ci       | utf16              | 118 |            | Yes         |       8 |
| utf16_estonian_ci        | utf16              | 107 |            | Yes         |       8 |
| utf16_general_ci         | utf16              |  54 | Yes        | Yes         |       1 |
| utf16_german2_ci         | utf16              | 121 |            | Yes         |       8 |
| utf16_hungarian_ci       | utf16              | 119 |            | Yes         |       8 |
| utf16_icelandic_ci       | utf16              | 102 |            | Yes         |       8 |
| utf16_latvian_ci         | utf16              | 103 |            | Yes         |       8 |
| utf16_lithuanian_ci      | utf16              | 113 |            | Yes         |       8 |
| utf16_persian_ci         | utf16              | 117 |            | Yes         |       8 |
| utf16_polish_ci          | utf16              | 106 |            | Yes         |       8 |
| utf16_romanian_ci        | utf16              | 104 |            | Yes         |       8 |
| utf16_roman_ci           | utf16              | 116 |            | Yes         |       8 |
| utf16_sinhala_ci         | utf16              | 120 |            | Yes         |       8 |
| utf16_slovak_ci          | utf16              | 114 |            | Yes         |       8 |
| utf16_slovenian_ci       | utf16              | 105 |            | Yes         |       8 |
| utf16_spanish2_ci        | utf16              | 115 |            | Yes         |       8 |
| utf16_spanish_ci         | utf16              | 108 |            | Yes         |       8 |
| utf16_swedish_ci         | utf16              | 109 |            | Yes         |       8 |
| utf16_turkish_ci         | utf16              | 110 |            | Yes         |       8 |
| utf16_unicode_520_ci     | utf16              | 123 |            | Yes         |       8 |
| utf16_unicode_ci         | utf16              | 101 |            | Yes         |       8 |
| utf16_vietnamese_ci      | utf16              | 124 |            | Yes         |       8 |
| utf32_bin                | utf32              |  61 |            | Yes         |       1 |
| utf32_croatian_ci        | utf32              | 181 |            | Yes         |       8 |
| utf32_czech_ci           | utf32              | 170 |            | Yes         |       8 |
| utf32_danish_ci          | utf32              | 171 |            | Yes         |       8 |
| utf32_esperanto_ci       | utf32              | 177 |            | Yes         |       8 |
| utf32_estonian_ci        | utf32              | 166 |            | Yes         |       8 |
| utf32_general_ci         | utf32              |  60 | Yes        | Yes         |       1 |
| utf32_german2_ci         | utf32              | 180 |            | Yes         |       8 |
| utf32_hungarian_ci       | utf32              | 178 |            | Yes         |       8 |
| utf32_icelandic_ci       | utf32              | 161 |            | Yes         |       8 |
| utf32_latvian_ci         | utf32              | 162 |            | Yes         |       8 |
| utf32_lithuanian_ci      | utf32              | 172 |            | Yes         |       8 |
| utf32_persian_ci         | utf32              | 176 |            | Yes         |       8 |
| utf32_polish_ci          | utf32              | 165 |            | Yes         |       8 |
| utf32_romanian_ci        | utf32              | 163 |            | Yes         |       8 |
| utf32_roman_ci           | utf32              | 175 |            | Yes         |       8 |
| utf32_sinhala_ci         | utf32              | 179 |            | Yes         |       8 |
| utf32_slovak_ci          | utf32              | 173 |            | Yes         |       8 |
| utf32_slovenian_ci       | utf32              | 164 |            | Yes         |       8 |
| utf32_spanish2_ci        | utf32              | 174 |            | Yes         |       8 |
| utf32_spanish_ci         | utf32              | 167 |            | Yes         |       8 |
| utf32_swedish_ci         | utf32              | 168 |            | Yes         |       8 |
| utf32_turkish_ci         | utf32              | 169 |            | Yes         |       8 |
| utf32_unicode_520_ci     | utf32              | 182 |            | Yes         |       8 |
| utf32_unicode_ci         | utf32              | 160 |            | Yes         |       8 |
| utf32_vietnamese_ci      | utf32              | 183 |            | Yes         |       8 |
| utf8mb4_bin              | utf8mb4            |  46 |            | Yes         |       1 |
| utf8mb4_croatian_ci      | utf8mb4            | 245 |            | Yes         |       8 |
| utf8mb4_czech_ci         | utf8mb4            | 234 |            | Yes         |       8 |
| utf8mb4_danish_ci        | utf8mb4            | 235 |            | Yes         |       8 |
| utf8mb4_esperanto_ci     | utf8mb4            | 241 |            | Yes         |       8 |
| utf8mb4_estonian_ci      | utf8mb4            | 230 |            | Yes         |       8 |
| utf8mb4_general_ci       | utf8mb4            |  45 | Yes        | Yes         |       1 |
| utf8mb4_german2_ci       | utf8mb4            | 244 |            | Yes         |       8 |
| utf8mb4_hungarian_ci     | utf8mb4            | 242 |            | Yes         |       8 |
| utf8mb4_icelandic_ci     | utf8mb4            | 225 |            | Yes         |       8 |
| utf8mb4_latvian_ci       | utf8mb4            | 226 |            | Yes         |       8 |
| utf8mb4_lithuanian_ci    | utf8mb4            | 236 |            | Yes         |       8 |
| utf8mb4_persian_ci       | utf8mb4            | 240 |            | Yes         |       8 |
| utf8mb4_polish_ci        | utf8mb4            | 229 |            | Yes         |       8 |
| utf8mb4_romanian_ci      | utf8mb4            | 227 |            | Yes         |       8 |
| utf8mb4_roman_ci         | utf8mb4            | 239 |            | Yes         |       8 |
| utf8mb4_sinhala_ci       | utf8mb4            | 243 |            | Yes         |       8 |
| utf8mb4_slovak_ci        | utf8mb4            | 237 |            | Yes         |       8 |
| utf8mb4_slovenian_ci     | utf8mb4            | 228 |            | Yes         |       8 |
| utf8mb4_spanish2_ci      | utf8mb4            | 238 |            | Yes         |       8 |
| utf8mb4_spanish_ci       | utf8mb4            | 231 |            | Yes         |       8 |
| utf8mb4_swedish_ci       | utf8mb4            | 232 |            | Yes         |       8 |
| utf8mb4_turkish_ci       | utf8mb4            | 233 |            | Yes         |       8 |
| utf8mb4_unicode_520_ci   | utf8mb4            | 246 |            | Yes         |       8 |
| utf8mb4_unicode_ci       | utf8mb4            | 224 |            | Yes         |       8 |
| utf8mb4_vietnamese_ci    | utf8mb4            | 247 |            | Yes         |       8 |
| utf8_bin                 | utf8               |  83 |            | Yes         |       1 |
| utf8_croatian_ci         | utf8               | 213 |            | Yes         |       8 |
| utf8_czech_ci            | utf8               | 202 |            | Yes         |       8 |
| utf8_danish_ci           | utf8               | 203 |            | Yes         |       8 |
| utf8_esperanto_ci        | utf8               | 209 |            | Yes         |       8 |
| utf8_estonian_ci         | utf8               | 198 |            | Yes         |       8 |
| utf8_general_ci          | utf8               |  33 | Yes        | Yes         |       1 |
| utf8_general_mysql500_ci | utf8               | 223 |            | Yes         |       1 |
| utf8_german2_ci          | utf8               | 212 |            | Yes         |       8 |
| utf8_hungarian_ci        | utf8               | 210 |            | Yes         |       8 |
| utf8_icelandic_ci        | utf8               | 193 |            | Yes         |       8 |
| utf8_latvian_ci          | utf8               | 194 |            | Yes         |       8 |
| utf8_lithuanian_ci       | utf8               | 204 |            | Yes         |       8 |
| utf8_persian_ci          | utf8               | 208 |            | Yes         |       8 |
| utf8_polish_ci           | utf8               | 197 |            | Yes         |       8 |
| utf8_romanian_ci         | utf8               | 195 |            | Yes         |       8 |
| utf8_roman_ci            | utf8               | 207 |            | Yes         |       8 |
| utf8_sinhala_ci          | utf8               | 211 |            | Yes         |       8 |
| utf8_slovak_ci           | utf8               | 205 |            | Yes         |       8 |
| utf8_slovenian_ci        | utf8               | 196 |            | Yes         |       8 |
| utf8_spanish2_ci         | utf8               | 206 |            | Yes         |       8 |
| utf8_spanish_ci          | utf8               | 199 |            | Yes         |       8 |
| utf8_swedish_ci          | utf8               | 200 |            | Yes         |       8 |
| utf8_turkish_ci          | utf8               | 201 |            | Yes         |       8 |
| utf8_unicode_520_ci      | utf8               | 214 |            | Yes         |       8 |
| utf8_unicode_ci          | utf8               | 192 |            | Yes         |       8 |
| utf8_vietnamese_ci       | utf8               | 215 |            | Yes         |       8 |
+--------------------------+--------------------+-----+------------+-------------+---------+
219 rows in set (0.00 sec)


mysql> create database dao2  character set  utf8  COLLATE utf8_sinhala_ci;
Query OK, 1 row affected (0.05 sec)


--实例级别
mysql> show create database dao2 ;
+----------+---------------------------------------------------------------------------------------+
| Database | Create Database                                                                       |
+----------+---------------------------------------------------------------------------------------+
| dao2     | CREATE DATABASE `dao2` /*!40100 DEFAULT CHARACTER SET utf8 COLLATE utf8_sinhala_ci */ |
+----------+---------------------------------------------------------------------------------------+
1 row in set (0.00 sec)


mysql> create table dao2_1 (c varchar(10)) charset utf8mb4  COLLATE  utf8mb4_danish_ci
    -> ;
Query OK, 0 rows affected (0.06 sec)
--表级别
mysql> show create table dao2_1 ;
+--------+----------------------------------------------------------------------------------------------------------------------------------------------------+
| Table  | Create Table                                                                                                                                       |
+--------+----------------------------------------------------------------------------------------------------------------------------------------------------+
| dao2_1 | CREATE TABLE `dao2_1` (
  `c` varchar(10) COLLATE utf8mb4_danish_ci DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_danish_ci |
+--------+----------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
--列级别
mysql> show create table dao22 ;
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                             |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| dao22 | CREATE TABLE `dao22` (
  `a` varchar(10) CHARACTER SET utf16 COLLATE utf16_sinhala_ci DEFAULT NULL,
  `b` varchar(100) COLLATE utf8_sinhala_ci DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_sinhala_ci |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)


每一种字符集对应N中校验规则 COLLATIONS 表中IS_DEFAULT 指明了默认规则
mysql> select * from COLLATIONS order by 1 ,4 ;
+--------------------------+--------------------+-----+------------+-------------+---------+
| COLLATION_NAME           | CHARACTER_SET_NAME | ID  | IS_DEFAULT | IS_COMPILED | SORTLEN |
+--------------------------+--------------------+-----+------------+-------------+---------+
| armscii8_bin             | armscii8           |  64 |            | Yes         |       1 |
| armscii8_general_ci      | armscii8           |  32 | Yes        | Yes         |       1 |
| ascii_bin                | ascii              |  65 |            | Yes         |       1 |
| ascii_general_ci         | ascii              |  11 | Yes        | Yes         |       1 |


armscii8 对应两种规则 其中默认使用armscii8_general_ci


校验规则名称与大小写区分


*_bin: binary case sensitive collation,也就是说是区分大小写的 
*_cs: case sensitive collation,区分大小写 
*_ci: case insensitive collation,不区分大小写


详见下例


mysql> show create table dao22 ;
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                             |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| dao22 | CREATE TABLE `dao22` (
  `a` varchar(10) CHARACTER SET utf16 COLLATE utf16_sinhala_ci DEFAULT NULL,   --注意校验规则为utf16_sinhala_ci 不区分大小写
  `b` varchar(100) COLLATE utf8_sinhala_ci DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_sinhala_ci |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)


mysql> insert into dao22 values ('a','a') ,('B','B'),('c','c');
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0


mysql> commit ;
Query OK, 0 rows affected (0.00 sec)


mysql> select * from dao22 order by 1 ;
+------+------+
| a    | b    |
+------+------+
| a    | a    |
| B    | B    |
| c    | c    |
+------+------+
3 rows in set (0.00 sec)




mysql> select * from dao22 order by a  COLLATE utf16_bin ;
+------+------+
| a    | b    |
+------+------+
| B    | B    |
| a    | a    |
| c    | c    |
+------+------+
3 rows in set (0.00 sec)

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