Mediante una simple consulta SQL es posible listar el conjunto de caracteres y collation que utilizan las columnas de texto de todas las tablas dentro de una base de datos MySQL específica.
La tabla "columns" de la base de datos "information_schema" guarda información acerca de todas las columnas de las tablas.
Si se desea obtener un listado de todos los conjuntos de caracteres y collation de las diferentes columnas, pertenecientes a una base de datos específica, ejecutar la siguiente consulta SQL:
SELECT table_name,column_name,character_set_name,collation_name FROM information_schema.columns WHERE character_set_name!="NULL" AND table_schema="mi_base_de_datos";
Por ejemplo, las columnas de tipo texto (char, varchar) de todas las tablas de la base de datos "mi_base_de_datos"), utilizan los siguientes conjuntos de caracteres y collation:
mysql> SELECT table_name,column_name,character_set_name,collation_name FROM information_schema.columns WHERE table_schema="prod_nutrientes_20111018" AND character_set_name!="NULL"; +------------+-----------------+--------------------+-------------------+ | table_name | column_name | character_set_name | collation_name | +------------+-----------------+--------------------+-------------------+ | tabla1 | nombre | utf8 | utf8_spanish_ci | | tabla2 | titulo | utf8 | utf8_general_ci | | tabla2 | descripcion | utf8 | utf8_general_ci | | tabla2 | contenido | utf8 | utf8_general_ci | | tabla3 | nombre | utf8 | utf8_general_ci | | tabla3 | nombre_completo | utf8 | utf8_general_ci | | tabla3 | direccion | utf8 | utf8_general_ci | | tabla3 | descripcion | utf8 | utf8_general_ci | | tabla4 | categoria | latin1 | latin1_danish_ci | | tabla5 | seccion | latin1 | latin1_danish_ci | | tabla5 | campos | latin1 | latin1_danish_ci | | tabla5 | estado | latin1 | latin1_danish_ci | | tabla6 | grupo | latin1 | latin1_swedish_ci | | tabla7 | ruta | latin1 | latin1_general_ci | | tabla7 | nombre | latin1 | latin1_general_ci | | tabla7 | extension | latin1 | latin1_general_ci | | tabla7 | tipo | latin1 | latin1_general_ci | | tabla7 | titulo | utf8 | utf8_general_ci | +------------+-----------------+--------------------+-------------------+ 18 rows in set (0.00 sec)
En el resultado se observa el nombre de la tabla, el nombre de la columna y luego el charset y collation utilizado.
¿Qué es un charset y qué es "collation"?
Un conjunto de caracteres define los símbolos disponibles y su codificación, por ejemplo el conjunto de caracteres ASCII original posee 95 caracteres imprimibles, y la letra 'A' ('a' mayúscula) se codifica como el número decimal 65. Diferentes conjuntos de caracteres poseen diferentes símbolos disponibles y utilizan diferentes codificaciones para representarlos. Los más utilizados son "UTF-8" (Unicode), ASCII y "latin1" (ISO 8859-1).
Por otro lado, los "collation" son conjuntos de reglas que se aplican sobre un conjunto de caracteres, para comparar sus símbolos. Por ejemplo, el "collation" es quien determina si un conjunto de caracteres es o no sensible a mayúsculas (¿es 'A' igual a 'a'?), lo cual afecta las comparaciones y en definitiva el ordenamiento. Lo mismo ocurre para el caso de las tildes y diéresis en el idioma español, el "collation" es quien determina si 'a' es equivalente a 'á' en una comparación. Por ende, además de optar por un conjunto de caracteres, se debe elegir el collation adecuado que mejor se ajuste al nuestro idioma (o más bien al idioma de la aplicación que gestiona a los datos).
Si se desea conocer cuales son los conjuntos de caracteres disponibles en el motor, simplemente ejecutar:
SHOW CHARACTER SET;
Por ejemplo:
mysql> SHOW CHARACTER SET; +----------+-----------------------------+---------------------+--------+ | Charset | Description | Default collation | Maxlen | +----------+-----------------------------+---------------------+--------+ | big5 | Big5 Traditional Chinese | big5_chinese_ci | 2 | | dec8 | DEC West European | dec8_swedish_ci | 1 | | cp850 | DOS West European | cp850_general_ci | 1 | | hp8 | HP West European | hp8_english_ci | 1 | | koi8r | KOI8-R Relcom Russian | koi8r_general_ci | 1 | | latin1 | cp1252 West European | latin1_swedish_ci | 1 | | latin2 | ISO 8859-2 Central European | latin2_general_ci | 1 | | swe7 | 7bit Swedish | swe7_swedish_ci | 1 | | ascii | US ASCII | ascii_general_ci | 1 | | ujis | EUC-JP Japanese | ujis_japanese_ci | 3 | | sjis | Shift-JIS Japanese | sjis_japanese_ci | 2 | | hebrew | ISO 8859-8 Hebrew | hebrew_general_ci | 1 | | tis620 | TIS620 Thai | tis620_thai_ci | 1 | | euckr | EUC-KR Korean | euckr_korean_ci | 2 | | koi8u | KOI8-U Ukrainian | koi8u_general_ci | 1 | | gb2312 | GB2312 Simplified Chinese | gb2312_chinese_ci | 2 | | greek | ISO 8859-7 Greek | greek_general_ci | 1 | | cp1250 | Windows Central European | cp1250_general_ci | 1 | | gbk | GBK Simplified Chinese | gbk_chinese_ci | 2 | | latin5 | ISO 8859-9 Turkish | latin5_turkish_ci | 1 | | armscii8 | ARMSCII-8 Armenian | armscii8_general_ci | 1 | | utf8 | UTF-8 Unicode | utf8_general_ci | 3 | | ucs2 | UCS-2 Unicode | ucs2_general_ci | 2 | | cp866 | DOS Russian | cp866_general_ci | 1 | | keybcs2 | DOS Kamenicky Czech-Slovak | keybcs2_general_ci | 1 | | macce | Mac Central European | macce_general_ci | 1 | | macroman | Mac West European | macroman_general_ci | 1 | | cp852 | DOS Central European | cp852_general_ci | 1 | | latin7 | ISO 8859-13 Baltic | latin7_general_ci | 1 | | utf8mb4 | UTF-8 Unicode | utf8mb4_general_ci | 4 | | cp1251 | Windows Cyrillic | cp1251_general_ci | 1 | | utf16 | UTF-16 Unicode | utf16_general_ci | 4 | | cp1256 | Windows Arabic | cp1256_general_ci | 1 | | cp1257 | Windows Baltic | cp1257_general_ci | 1 | | utf32 | UTF-32 Unicode | utf32_general_ci | 4 | | binary | Binary pseudo charset | binary | 1 | | geostd8 | GEOSTD8 Georgian | geostd8_general_ci | 1 | | cp932 | SJIS for Windows Japanese | cp932_japanese_ci | 2 | | eucjpms | UJIS for Windows Japanese | eucjpms_japanese_ci | 3 | +----------+-----------------------------+---------------------+--------+ 39 rows in set (0.01 sec)
De igual forma, para conocer los collation disponibles, ejecutar:
SHOW COLLATION;
Por ejemplo:
mysql> SHOW COLLATION; +--------------------------+----------+-----+---------+----------+---------+ | Collation | Charset | Id | Default | Compiled | Sortlen | +--------------------------+----------+-----+---------+----------+---------+ | big5_chinese_ci | big5 | 1 | Yes | Yes | 1 | | big5_bin | big5 | 84 | | Yes | 1 | | dec8_swedish_ci | dec8 | 3 | Yes | Yes | 1 | | dec8_bin | dec8 | 69 | | Yes | 1 | | cp850_general_ci | cp850 | 4 | Yes | Yes | 1 | | cp850_bin | cp850 | 80 | | Yes | 1 | | hp8_english_ci | hp8 | 6 | Yes | Yes | 1 | | hp8_bin | hp8 | 72 | | Yes | 1 | | koi8r_general_ci | koi8r | 7 | Yes | Yes | 1 | | koi8r_bin | koi8r | 74 | | Yes | 1 | | latin1_german1_ci | latin1 | 5 | | Yes | 1 | | latin1_swedish_ci | latin1 | 8 | Yes | Yes | 1 | | latin1_danish_ci | latin1 | 15 | | Yes | 1 | | latin1_german2_ci | latin1 | 31 | | Yes | 2 | | latin1_bin | latin1 | 47 | | Yes | 1 | | latin1_general_ci | latin1 | 48 | | Yes | 1 | | latin1_general_cs | latin1 | 49 | | Yes | 1 | | latin1_spanish_ci | latin1 | 94 | | Yes | 1 | | latin2_czech_cs | latin2 | 2 | | Yes | 4 | | latin2_general_ci | latin2 | 9 | Yes | Yes | 1 | | latin2_hungarian_ci | latin2 | 21 | | Yes | 1 | | latin2_croatian_ci | latin2 | 27 | | Yes | 1 | | latin2_bin | latin2 | 77 | | Yes | 1 | | swe7_swedish_ci | swe7 | 10 | Yes | Yes | 1 | | swe7_bin | swe7 | 82 | | Yes | 1 | | ascii_general_ci | ascii | 11 | Yes | Yes | 1 | | ascii_bin | ascii | 65 | | Yes | 1 | | ujis_japanese_ci | ujis | 12 | Yes | Yes | 1 | | ujis_bin | ujis | 91 | | Yes | 1 | | sjis_japanese_ci | sjis | 13 | Yes | Yes | 1 | | sjis_bin | sjis | 88 | | Yes | 1 | | hebrew_general_ci | hebrew | 16 | Yes | Yes | 1 | | hebrew_bin | hebrew | 71 | | Yes | 1 | | tis620_thai_ci | tis620 | 18 | Yes | Yes | 4 | | tis620_bin | tis620 | 89 | | Yes | 1 | | euckr_korean_ci | euckr | 19 | Yes | Yes | 1 | | euckr_bin | euckr | 85 | | Yes | 1 | | koi8u_general_ci | koi8u | 22 | Yes | Yes | 1 | | koi8u_bin | koi8u | 75 | | Yes | 1 | | gb2312_chinese_ci | gb2312 | 24 | Yes | Yes | 1 | | gb2312_bin | gb2312 | 86 | | Yes | 1 | | greek_general_ci | greek | 25 | Yes | Yes | 1 | | greek_bin | greek | 70 | | Yes | 1 | | cp1250_general_ci | cp1250 | 26 | Yes | Yes | 1 | | cp1250_czech_cs | cp1250 | 34 | | Yes | 2 | | cp1250_croatian_ci | cp1250 | 44 | | Yes | 1 | | cp1250_bin | cp1250 | 66 | | Yes | 1 | | cp1250_polish_ci | cp1250 | 99 | | Yes | 1 | | gbk_chinese_ci | gbk | 28 | Yes | Yes | 1 | | gbk_bin | gbk | 87 | | Yes | 1 | | latin5_turkish_ci | latin5 | 30 | Yes | Yes | 1 | | latin5_bin | latin5 | 78 | | Yes | 1 | | armscii8_general_ci | armscii8 | 32 | Yes | Yes | 1 | | armscii8_bin | armscii8 | 64 | | Yes | 1 | | utf8_general_ci | utf8 | 33 | Yes | Yes | 1 | | utf8_bin | utf8 | 83 | | Yes | 1 | | utf8_unicode_ci | utf8 | 192 | | Yes | 8 | | utf8_icelandic_ci | utf8 | 193 | | Yes | 8 | | utf8_latvian_ci | utf8 | 194 | | Yes | 8 | | utf8_romanian_ci | utf8 | 195 | | Yes | 8 | | utf8_slovenian_ci | utf8 | 196 | | Yes | 8 | | utf8_polish_ci | utf8 | 197 | | Yes | 8 | | utf8_estonian_ci | utf8 | 198 | | Yes | 8 | | utf8_spanish_ci | utf8 | 199 | | Yes | 8 | | utf8_swedish_ci | utf8 | 200 | | Yes | 8 | | utf8_turkish_ci | utf8 | 201 | | Yes | 8 | | utf8_czech_ci | utf8 | 202 | | Yes | 8 | | utf8_danish_ci | utf8 | 203 | | Yes | 8 | | utf8_lithuanian_ci | utf8 | 204 | | Yes | 8 | | utf8_slovak_ci | utf8 | 205 | | Yes | 8 | | utf8_spanish2_ci | utf8 | 206 | | Yes | 8 | | utf8_roman_ci | utf8 | 207 | | Yes | 8 | | utf8_persian_ci | utf8 | 208 | | Yes | 8 | | utf8_esperanto_ci | utf8 | 209 | | Yes | 8 | | utf8_hungarian_ci | utf8 | 210 | | Yes | 8 | | utf8_sinhala_ci | utf8 | 211 | | Yes | 8 | | utf8_general_mysql500_ci | utf8 | 223 | | Yes | 1 | | ucs2_general_ci | ucs2 | 35 | Yes | Yes | 1 | | ucs2_bin | ucs2 | 90 | | Yes | 1 | | ucs2_unicode_ci | ucs2 | 128 | | Yes | 8 | | ucs2_icelandic_ci | ucs2 | 129 | | Yes | 8 | | ucs2_latvian_ci | ucs2 | 130 | | Yes | 8 | | ucs2_romanian_ci | ucs2 | 131 | | Yes | 8 | | ucs2_slovenian_ci | ucs2 | 132 | | Yes | 8 | | ucs2_polish_ci | ucs2 | 133 | | Yes | 8 | | ucs2_estonian_ci | ucs2 | 134 | | Yes | 8 | | ucs2_spanish_ci | ucs2 | 135 | | Yes | 8 | | ucs2_swedish_ci | ucs2 | 136 | | Yes | 8 | | ucs2_turkish_ci | ucs2 | 137 | | Yes | 8 | | ucs2_czech_ci | ucs2 | 138 | | Yes | 8 | | ucs2_danish_ci | ucs2 | 139 | | Yes | 8 | | ucs2_lithuanian_ci | ucs2 | 140 | | Yes | 8 | | ucs2_slovak_ci | ucs2 | 141 | | Yes | 8 | | ucs2_spanish2_ci | ucs2 | 142 | | Yes | 8 | | ucs2_roman_ci | ucs2 | 143 | | Yes | 8 | | ucs2_persian_ci | ucs2 | 144 | | Yes | 8 | | ucs2_esperanto_ci | ucs2 | 145 | | Yes | 8 | | ucs2_hungarian_ci | ucs2 | 146 | | Yes | 8 | | ucs2_sinhala_ci | ucs2 | 147 | | Yes | 8 | | ucs2_general_mysql500_ci | ucs2 | 159 | | Yes | 1 | | cp866_general_ci | cp866 | 36 | Yes | Yes | 1 | | cp866_bin | cp866 | 68 | | Yes | 1 | | keybcs2_general_ci | keybcs2 | 37 | Yes | Yes | 1 | | keybcs2_bin | keybcs2 | 73 | | Yes | 1 | | macce_general_ci | macce | 38 | Yes | Yes | 1 | | macce_bin | macce | 43 | | Yes | 1 | | macroman_general_ci | macroman | 39 | Yes | Yes | 1 | | macroman_bin | macroman | 53 | | Yes | 1 | | cp852_general_ci | cp852 | 40 | Yes | Yes | 1 | | cp852_bin | cp852 | 81 | | Yes | 1 | | latin7_estonian_cs | latin7 | 20 | | Yes | 1 | | latin7_general_ci | latin7 | 41 | Yes | Yes | 1 | | latin7_general_cs | latin7 | 42 | | Yes | 1 | | latin7_bin | latin7 | 79 | | Yes | 1 | | utf8mb4_general_ci | utf8mb4 | 45 | Yes | Yes | 1 | | utf8mb4_bin | utf8mb4 | 46 | | Yes | 1 | | utf8mb4_unicode_ci | utf8mb4 | 224 | | Yes | 8 | | utf8mb4_icelandic_ci | utf8mb4 | 225 | | Yes | 8 | | utf8mb4_latvian_ci | utf8mb4 | 226 | | Yes | 8 | | utf8mb4_romanian_ci | utf8mb4 | 227 | | Yes | 8 | | utf8mb4_slovenian_ci | utf8mb4 | 228 | | Yes | 8 | | utf8mb4_polish_ci | utf8mb4 | 229 | | Yes | 8 | | utf8mb4_estonian_ci | utf8mb4 | 230 | | Yes | 8 | | utf8mb4_spanish_ci | utf8mb4 | 231 | | Yes | 8 | | utf8mb4_swedish_ci | utf8mb4 | 232 | | Yes | 8 | | utf8mb4_turkish_ci | utf8mb4 | 233 | | Yes | 8 | | utf8mb4_czech_ci | utf8mb4 | 234 | | Yes | 8 | | utf8mb4_danish_ci | utf8mb4 | 235 | | Yes | 8 | | utf8mb4_lithuanian_ci | utf8mb4 | 236 | | Yes | 8 | | utf8mb4_slovak_ci | utf8mb4 | 237 | | Yes | 8 | | utf8mb4_spanish2_ci | utf8mb4 | 238 | | Yes | 8 | | utf8mb4_roman_ci | utf8mb4 | 239 | | Yes | 8 | | utf8mb4_persian_ci | utf8mb4 | 240 | | Yes | 8 | | utf8mb4_esperanto_ci | utf8mb4 | 241 | | Yes | 8 | | utf8mb4_hungarian_ci | utf8mb4 | 242 | | Yes | 8 | | utf8mb4_sinhala_ci | utf8mb4 | 243 | | Yes | 8 | | cp1251_bulgarian_ci | cp1251 | 14 | | Yes | 1 | | cp1251_ukrainian_ci | cp1251 | 23 | | Yes | 1 | | cp1251_bin | cp1251 | 50 | | Yes | 1 | | cp1251_general_ci | cp1251 | 51 | Yes | Yes | 1 | | cp1251_general_cs | cp1251 | 52 | | Yes | 1 | | utf16_general_ci | utf16 | 54 | Yes | Yes | 1 | | utf16_bin | utf16 | 55 | | Yes | 1 | | utf16_unicode_ci | utf16 | 101 | | Yes | 8 | | utf16_icelandic_ci | utf16 | 102 | | Yes | 8 | | utf16_latvian_ci | utf16 | 103 | | Yes | 8 | | utf16_romanian_ci | utf16 | 104 | | Yes | 8 | | utf16_slovenian_ci | utf16 | 105 | | Yes | 8 | | utf16_polish_ci | utf16 | 106 | | Yes | 8 | | utf16_estonian_ci | utf16 | 107 | | Yes | 8 | | utf16_spanish_ci | utf16 | 108 | | Yes | 8 | | utf16_swedish_ci | utf16 | 109 | | Yes | 8 | | utf16_turkish_ci | utf16 | 110 | | Yes | 8 | | utf16_czech_ci | utf16 | 111 | | Yes | 8 | | utf16_danish_ci | utf16 | 112 | | Yes | 8 | | utf16_lithuanian_ci | utf16 | 113 | | Yes | 8 | | utf16_slovak_ci | utf16 | 114 | | Yes | 8 | | utf16_spanish2_ci | utf16 | 115 | | Yes | 8 | | utf16_roman_ci | utf16 | 116 | | Yes | 8 | | utf16_persian_ci | utf16 | 117 | | Yes | 8 | | utf16_esperanto_ci | utf16 | 118 | | Yes | 8 | | utf16_hungarian_ci | utf16 | 119 | | Yes | 8 | | utf16_sinhala_ci | utf16 | 120 | | Yes | 8 | | cp1256_general_ci | cp1256 | 57 | Yes | Yes | 1 | | cp1256_bin | cp1256 | 67 | | Yes | 1 | | cp1257_lithuanian_ci | cp1257 | 29 | | Yes | 1 | | cp1257_bin | cp1257 | 58 | | Yes | 1 | | cp1257_general_ci | cp1257 | 59 | Yes | Yes | 1 | | utf32_general_ci | utf32 | 60 | Yes | Yes | 1 | | utf32_bin | utf32 | 61 | | Yes | 1 | | utf32_unicode_ci | utf32 | 160 | | Yes | 8 | | utf32_icelandic_ci | utf32 | 161 | | Yes | 8 | | utf32_latvian_ci | utf32 | 162 | | Yes | 8 | | utf32_romanian_ci | utf32 | 163 | | Yes | 8 | | utf32_slovenian_ci | utf32 | 164 | | Yes | 8 | | utf32_polish_ci | utf32 | 165 | | Yes | 8 | | utf32_estonian_ci | utf32 | 166 | | Yes | 8 | | utf32_spanish_ci | utf32 | 167 | | Yes | 8 | | utf32_swedish_ci | utf32 | 168 | | Yes | 8 | | utf32_turkish_ci | utf32 | 169 | | Yes | 8 | | utf32_czech_ci | utf32 | 170 | | Yes | 8 | | utf32_danish_ci | utf32 | 171 | | Yes | 8 | | utf32_lithuanian_ci | utf32 | 172 | | Yes | 8 | | utf32_slovak_ci | utf32 | 173 | | Yes | 8 | | utf32_spanish2_ci | utf32 | 174 | | Yes | 8 | | utf32_roman_ci | utf32 | 175 | | Yes | 8 | | utf32_persian_ci | utf32 | 176 | | Yes | 8 | | utf32_esperanto_ci | utf32 | 177 | | Yes | 8 | | utf32_hungarian_ci | utf32 | 178 | | Yes | 8 | | utf32_sinhala_ci | utf32 | 179 | | Yes | 8 | | binary | binary | 63 | Yes | Yes | 1 | | geostd8_general_ci | geostd8 | 92 | Yes | Yes | 1 | | geostd8_bin | geostd8 | 93 | | Yes | 1 | | cp932_japanese_ci | cp932 | 95 | Yes | Yes | 1 | | cp932_bin | cp932 | 96 | | Yes | 1 | | eucjpms_japanese_ci | eucjpms | 97 | Yes | Yes | 1 | | eucjpms_bin | eucjpms | 98 | | Yes | 1 | +--------------------------+----------+-----+---------+----------+---------+ 197 rows in set (0.00 sec)
Actualmente el conjunto de caracteres UTF-8 es el más utilizado, y es casi un estándar en Internet. Si se va a utilizar el mismo en una aplicación cuyo idioma es el español, es recomendable utilizarlo en combinación con el collation utf8_spanish_ci (español moderno) ó utf8_spanish2_ci (español tradicional). Pero se debe tener en cuenta que diferentes "collation" poseen diferentes reglas. Por ejemplo, a diferencia del español moderno, el español tradicional considera a "ch" y "ll" como letras adicionales (¿recuerdan el viejo abecedario en el colegio primario? a, b, c, ch, d, e...), lo cual puede afectar notablemente el ordenamiento.
Párrafo extraído del manual de MySQL:
The xxx_spanish_ci and xxx_spanish2_ci collations correspond to modern Spanish and traditional Spanish, respectively. In both collations, “ñ” (n-tilde) is a separate letter between “n” and “o”. In addition, for traditional Spanish, “ch” is a separate letter between “c” and “d”, and “ll” is a separate letter between “l” and “m”
Por último, se debe tener en cuenta que mezclar charsets dentro de una misma aplicación es un error garrafal. Lamentablemente muy común entre los desarrolladores, tal vez por por desconocimiento o descuido. ¿Qué sucede si en una aplicación Web necesitamos mostrar datos de columnas que utilizan diferentes charsets en una misma página? Sea cual sea el conjunto de caracteres que especifiquemos en el código HTML, o en el header de la respuesta del servidor Web, algunos de los datos serán visualizados de forma incorrecta (muy probablemente cuando se utilizan tildes y caracteres especiales). Esto se debe a que diferentes charsets codifican a los caracteres de diferente forma.
Fuente: linuxito
