返回字符串str的最左面字符的ASCII代码值。如果str是空字符串，返回0。如果str是NULL，返回NULL
举例：
1.
mysql> select ascii('hi');
+————-+
| ascii('hi') |
+————-+
| 104 |
+————-+
1 row in set
104是h的ASCII值
2.输出b和B的ASCII值
mysql> SELECT ASCII('b')AS Lower_Case, ASCII('B') AS Upper_Case;
+————+————+
| Lower_Case | Upper_Case |
+————+————+
| 98 | 66 |
+————+————+
1 row in set
3.在where语句中使用ASCII函数
输出aut_name首字母的ASCII值小于70的数据
SELECT aut_name,ASCII(aut_name)as "ASCII value of 1st character"
FROM author
WHERE ASCII(aut_name)<70;
4.输出字段中不存在没有ASCII值的数据
SELECT * FROM table_name WHERE NOT column_to_check REGEXP '[A-Za-z0-9.,-]';
5.与SUBSTRING一起使用计算字符串第二个以后的ASCII值
mysql> select ASCII(SUBSTRING('database',2,1));
+———————————-+
| ASCII(SUBSTRING('database',2,1)) |
+———————————-+
| 97 |
+———————————-+
1 row in set
ORD() 函数返回字符串第一个字符的ASCII 值。
语法： ORD(string)
举一些简单的例子：
mysql> SELECT ORD('i');
+----------+
| ORD('i') |
+----------+
| 105 |
+----------+
1 row in set
或者：
mysql> SELECT ORD('NowaMagic');
+------------------+
| ORD('NowaMagic') |
+------------------+
| 78 |
+------------------+
1 row in set
如果汉字又如何呢？
mysql> SELECT ORD('简明现代魔法');
+---------------------+
| ORD('简明现代魔法') |
+---------------------+
| 15183488 |
+---------------------+
1 row in set
mysql> SELECT ORD('简');
+-----------+
| ORD('简') |
+-----------+
| 15183488 |
+-----------+
1 row in set
为什么会有 8 位数那么长呢？原因是数据库使用的字符集问题，此处的数据库使用的是 UTF-8，16位表示一个符号。顺便贴一下SQL的执行语句：
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
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