1. 创建数据库
sql
CREATE DATABASE [IF NOT EXISTS] db_name
[create_specification [, create_specification] ...];-
大写的表示关键字 ：关键字规范使用大写，例如
CREATE DATABASE。 -
[ ]是可选项：表示括号内的内容是可选的。 -
CHARACTER SET：指定数据库采用的字符集，例如utf8。 -
COLLATE：指定数据库字符集的校验规则，例如utf8_general_ci。
在 MySQL 中，SQL 语句的关键字（如 CREATE DATABASE、SELECT、INSERT 等）不区分大小写。这意味着以下两条语句在 MySQL 中是完全等效的：
sql
CREATE DATABASE mydb;
create database mydb;数据库名、表名、列名等标识符：MySQL 对这些标识符的大小写敏感性取决于操作系统和 MySQL 的配置。
在 Windows 系统上 ：数据库名和表名是大小写不敏感的：mydb 和 MYDB 被视为同一个数据库。
在 Linux 系统上 ：数据库名和表名是大小写敏感的：mydb 和 MYDB 被视为不同的数据库。
列名 ：在所有系统上，列名默认是大小写不敏感的：name 和 NAME 在查询中被视为相同的列。
字符串比较：字符串的大小写敏感性取决于所使用的字符集和校验规则，下面会具体说明！
SQL 标准 ：SQL 标准建议关键字使用大写，标识符使用小写。虽然 MySQL 不强制要求，但遵循这一标准可以使代码更具可读性和一致性。
sql
CREATE DATABASE mydb;
CREATE TABLE mytable (
id INT,
name VARCHAR(50)
);总的来说：
-
关键字大小写 ：MySQL 不区分大小写，但建议使用大写以提高可读性。
-
标识符大小写 ：取决于操作系统和配置，建议统一使用小写以避免混淆。
-
字符串大小写 ：取决于字符集和校验规则，需要根据具体需求选择合适的校验规则。
2. 创建数据库案例
创建名为db1的数据库
sql
CREATE DATABASE db1;当我们创建数据库没有指定字符集和校验规则时，系统使用默认字符集：utf8，校验规则是：utf8_general_ci。在 " 3. 字符集和校验规则 " 我们可以通过相关命令查看！
创建一个使用utf8字符集的db2数据库
sql
CREATE DATABASE db2 CHARACTER SET utf8;创建一个使用utf8字符集，并带校对规则的db3数据库
sql
CREATE DATABASE db3 CHARACTER SET utf8 COLLATE utf8_general_ci;3. 字符集和校验规则
3.1 查看系统默认字符集以及校验规则
cpp
SHOW VARIABLES LIKE 'character_set_database';
SHOW VARIABLES LIKE 'collation_database';
sql
mysql> SHOW VARIABLES LIKE 'character_set_database';
+------------------------+-------+
| Variable_name | Value |
+------------------------+-------+
| character_set_database | utf8 |
+------------------------+-------+
1 row in set (0.02 sec)
mysql> SHOW VARIABLES LIKE 'collation_database';
+--------------------+-----------------+
| Variable_name | Value |
+--------------------+-----------------+
| collation_database | utf8_general_ci |
+--------------------+-----------------+
1 row in set (0.00 sec)3.2 查看数据库支持的字符集
sql
SHOW CHARSET;
show charset;
sql
mysql> SHOW CHARSET;
+----------+---------------------------------+---------------------+--------+
| 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 |
| utf16le | UTF-16LE Unicode | utf16le_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 |
| gb18030 | China National Standard GB18030 | gb18030_chinese_ci | 4 |
+----------+---------------------------------+---------------------+--------+
41 rows in set (0.00 sec)字符集主要是控制用什么语言。例如，utf8可以使用中文。
3.3 查看数据库支持的字符集校验规则
sql
SHOW COLLATION;
show collation;
sql
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_german2_ci | utf8 | 212 | | Yes | 8 |
| utf8_croatian_ci | utf8 | 213 | | Yes | 8 |
| utf8_unicode_520_ci | utf8 | 214 | | Yes | 8 |
| utf8_vietnamese_ci | utf8 | 215 | | 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_german2_ci | ucs2 | 148 | | Yes | 8 |
| ucs2_croatian_ci | ucs2 | 149 | | Yes | 8 |
| ucs2_unicode_520_ci | ucs2 | 150 | | Yes | 8 |
| ucs2_vietnamese_ci | ucs2 | 151 | | 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 |
| utf8mb4_german2_ci | utf8mb4 | 244 | | Yes | 8 |
| utf8mb4_croatian_ci | utf8mb4 | 245 | | Yes | 8 |
| utf8mb4_unicode_520_ci | utf8mb4 | 246 | | Yes | 8 |
| utf8mb4_vietnamese_ci | utf8mb4 | 247 | | 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 |
| utf16_german2_ci | utf16 | 121 | | Yes | 8 |
| utf16_croatian_ci | utf16 | 122 | | Yes | 8 |
| utf16_unicode_520_ci | utf16 | 123 | | Yes | 8 |
| utf16_vietnamese_ci | utf16 | 124 | | Yes | 8 |
| utf16le_general_ci | utf16le | 56 | Yes | Yes | 1 |
| utf16le_bin | utf16le | 62 | | Yes | 1 |
| 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 |
| utf32_german2_ci | utf32 | 180 | | Yes | 8 |
| utf32_croatian_ci | utf32 | 181 | | Yes | 8 |
| utf32_unicode_520_ci | utf32 | 182 | | Yes | 8 |
| utf32_vietnamese_ci | utf32 | 183 | | 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 |
| gb18030_chinese_ci | gb18030 | 248 | Yes | Yes | 2 |
| gb18030_bin | gb18030 | 249 | | Yes | 1 |
| gb18030_unicode_520_ci | gb18030 | 250 | | Yes | 8 |
+--------------------------+----------+-----+---------+----------+---------+
222 rows in set (0.00 sec)3.4 校验规则对数据库的影响
不区分大小写：
创建一个数据库，校验规则使用utf8_general_ci（不区分大小写）。
sql
CREATE DATABASE test1 COLLATE utf8_general_ci;
USE test1;
CREATE TABLE person(name VARCHAR(20));
INSERT INTO person VALUES ('a'), ('A'), ('b'), ('B');查询结果：
sql
SELECT * FROM person WHERE name='a';输出：
sql
+------+
| name |
+------+
| a |
| A |
+------+区分大小写：
创建一个数据库，校验规则使用utf8_bin（区分大小写）。
sql
CREATE DATABASE test2 COLLATE utf8_bin;
USE test2;
CREATE TABLE person(name VARCHAR(20));
INSERT INTO person VALUES ('a'), ('A'), ('b'), ('B');查询结果：
sql
SELECT * FROM person WHERE name='a';输出：
sql
+------+
| name |
+------+
| a |
+------+结果排序：
不区分大小写排序以及结果：
sql
USE test1;
SELECT * FROM person ORDER BY name;输出：
sql
+------+
| name |
+------+
| a |
| A |
| b |
| B |
+------+区分大小写排序以及结果：
sql
USE test2;
SELECT * FROM person ORDER BY name;输出：
sql
+------+
| name |
+------+
| A |
| B |
| a |
| b |
+------+4. 操纵数据库
4.1 查看数据库
sql
SHOW DATABASES;4.2 显示创建语句
sql
SHOW CREATE DATABASE 数据库名;
sql
SHOW CREATE DATABASE mytest;输出：
sql
+----------+-----------------------------------------------------+
| Database | Create Database |
+----------+-----------------------------------------------------+
| mytest | CREATE DATABASE `mytest` /*!40100 DEFAULT CHARACTER SET utf8 */ |
+----------+-----------------------------------------------------+-
MySQL建议关键字使用大写，但不是必须的。
-
数据库名字的反引号`是为了防止使用的数据库名刚好是关键字。
-
/*!40100 default.... */：这不是注释，表示当前MySQL版本大于4.01版本时，就执行这句话。
4.3 修改数据库
sql
ALTER DATABASE db_name
[alter_specification [, alter_specification] ...];对数据库的修改主要指的是修改数据库的字符集和校验规则。
将mytest数据库字符集改成gbk：
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ALTER DATABASE mytest CHARACTER SET gbk;查看修改后的创建语句：
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SHOW CREATE DATABASE mytest;输出：
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+----------+-----------------------------------------------------+
| Database | Create Database |
+----------+-----------------------------------------------------+
| mytest | CREATE DATABASE `mytest` /*!40100 DEFAULT CHARACTER SET gbk */ |
+----------+-----------------------------------------------------+4.4 数据库删除
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DROP DATABASE [IF EXISTS] db_name;执行删除之后的结果：
-
数据库内部看不到对应的数据库。
-
对应的数据库文件夹被删除，级联删除，里面的数据表全部被删除。
-
注意：要随意删除数据库，因为一旦删除，数据将无法恢复。
4.5 备份和恢复
4.5.1 备份
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mysqldump -u 用户名 -p 数据库名 > 文件名.sql将mytest库备份到文件（退出连接）：
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mysqldump -u root -p mytest > mytest.sql这时，可以打开看看mytest.sql文件里的内容，其实把我们整个创建数据库、建表、导入数据的语句都装载这个文件中。
4.5.2 还原
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mysql -u 用户名 -p 数据库名 < 文件名.sql还原mytest库：
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mysql -u root -p mytest < mytest.sql4.5.3 注意事项
如果备份的不是整个数据库，而是其中的一张表，怎么做？
- 还是可以使用
mysqldump备份单张表，例如：
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mysqldump -u root -p 数据库名 表名 > 表名.sql同时备份多个数据库：
- 可以使用
--databases参数，例如：
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mysqldump -u root -p --databases 数据库1 数据库2 > 多库备份.sql如果备份一个数据库时，没有带上-B参数，在恢复数据库时，需要先创建空数据库，然后使用数据库，再使用source来还原：
详细解释
- 备份数据库时没有使用
-B参数假设你有一个名为
mytest的数据库，你使用以下命令备份它：bash
复制
sqlmysqldump -u root -p mytest > mytest_backup.sql这个命令会将
mytest数据库中的所有表和数据导出到一个 SQL 文件mytest_backup.sql中。注意，这里没有使用-B参数。
- 恢复数据库时的步骤
由于备份文件中只包含了表和数据的定义，而没有包含创建数据库的语句，因此在恢复数据时，需要手动创建一个空的数据库，然后导入备份文件。
步骤 1：创建一个空的数据库
sqlCREATE DATABASE mytest;步骤 2：切换到该数据库
sqlUSE mytest;步骤 3：使用
source命令导入备份文件在 MySQL 的命令行客户端中，使用
source命令来导入备份文件：
sqlSOURCE /path/to/mytest_backup.sql;具体示例：
假设你的备份文件路径是
/home/user/mytest_backup.sql，以下是完整的恢复过程：
登录到 MySQL
sqlmysql -u root -p创建一个空的数据库
sqlCREATE DATABASE mytest;切换到该数据库
sqlUSE mytest;导入备份文件
sqlSOURCE /home/user/mytest_backup.sql;如果使用
-B参数如果你在备份时使用了
-B参数，例如：
sqlmysqldump -u root -p -B mytest > mytest_backup.sql那么备份文件中会包含创建数据库的语句。在这种情况下，恢复时可以直接导入备份文件，而不需要手动创建数据库。例如：
sqlmysql -u root -p < /home/user/mytest_backup.sql所以说：
如果备份时没有使用
-B参数，恢复时需要手动创建一个空的数据库，然后切换到该数据库，最后使用source命令导入备份文件。如果备份时使用了
-B参数，恢复时可以直接导入备份文件，无需手动创建数据库。
4.6 查看连接情况
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SHOW PROCESSLIST;
show processlist;输出示例：
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+----+------+-----------+------+---------+------+-------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------+------+---------+------+-------+------------------+
| 1 | root | localhost | mytest | Sleep | 10 | | |
| 2 | user | localhost | mytest | Query | 0 | | SHOW PROCESSLIST |
+----+------+-----------+------+---------+------+-------+------------------+-
可以告诉我们当前有哪些用户连接到我们的MySQL。
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如果查出某个用户不是你正常登录的，很有可能你的数据库被人入侵了。
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当发现数据库比较慢时，可以用这个指令来查看数据库连接情况。