MySQL數(shù)據(jù)類(lèi)型--------字符串類(lèi)型實(shí)戰(zhàn)

1. 背景

  * MySQL支持的字符串類(lèi)型有CHAR、VARCHAR、二進(jìn)制、var二進(jìn)制、BLOB、文本等等。

2. 字符串類(lèi)型所需的存儲(chǔ)和值范圍

3. 定義與變長(zhǎng)區(qū)別 (CHAR VS VARCHAR)

4. 字符串類(lèi)型相關(guān)注意事項(xiàng)

   * 在BLOB和TEXT列上創(chuàng)建索引時(shí)，必須制定索引前綴的長(zhǎng)度

   * VARCHAR和VARBINARY必須長(zhǎng)度是可選的

   * BLOB和TEXT列不能有默認(rèn)值

   * BLOB和TEXT列排序時(shí)只使用該列的前max_sort_length個(gè)字節(jié)

mysql> show variables like 'max_sort_length';
+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| max_sort_length | 1024  |
+-----------------+-------+
1 row in set (0.01 sec)

5. 字符串類(lèi)型與排序規(guī)則

　 * 查看字符串相關(guān)信息　[ Default collation: 默認(rèn)排序規(guī)則 ]

mysql> show character set like 'utf8mb4';
+---------+---------------+--------------------+--------+
| Charset | Description   | Default collation  | Maxlen |
+---------+---------------+--------------------+--------+
| utf8mb4 | UTF-8 Unicode | utf8mb4_general_ci |      4 |
+---------+---------------+--------------------+--------+
1 row in set (0.01 sec)

　 * 查看utfmb4所有排序規(guī)則

mysql> show collation like 'utf8mb4%';
+------------------------+---------+-----+---------+----------+---------+
| Collation              | Charset | Id  | Default | Compiled | Sortlen |
+------------------------+---------+-----+---------+----------+---------+
| 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_spanish3_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 |
+------------------------+---------+-----+---------+----------+---------+
26 rows in set (0.00 sec)

　 * 修改默認(rèn)排序規(guī)則

mysql> set names utf8mb4 collate utf8mb4_bin;
Query OK, 0 rows affected (0.00 sec)

mysql> show character set like 'utf8mb4';
+---------+---------------+--------------------+--------+
| Charset | Description   | Default collation  | Maxlen |
+---------+---------------+--------------------+--------+
| utf8mb4 | UTF-8 Unicode | utf8mb4_general_ci |      4 |
+---------+---------------+--------------------+--------+
1 row in set (0.00 sec)

6. 總結(jié)

以需求驅(qū)動(dòng)技術(shù)，技術(shù)本身沒(méi)有優(yōu)略之分，只有業(yè)務(wù)之分。