返回字符的字符函数 1、CHR(n) [n为正整数，如果ngt;256，就去MOD(n,256)] select CHR(65) a1,CHR(67)||CHR(65)||CHR(84) a2 FR
返回字符的字符函数
1、CHR(n) [n为正整数，如果n>256，就去MOD(n,256)]
2、CONCAT(ch1,ch2) 拼接字符串[cha1,ch2为任意字符CHAR, VARCHAR2, NCHAR, NVARCHAR2, CLOB, NCLOB]
CONCAT(CLOB, NCLOB) returns NCLOB
CONCAT(NCLOB, NCHAR) returns NCLOB
CONCAT(NCLOB, CHAR) returns NCLOB
CONCAT(NCHAR, CLOB) returns NCLOB
3、INITCAP(ch) 单次首字母大写，其他小写
4、LOWER(ch) 将字符串转换为小写
5、LPAD(expr1,n,expr2) 从expr1中截取n个字符返回，如果长度不够就用expr2填充左边
6、LTRIM(ch,set)将字符串ch左边的包含在set中的字符移除，如股票不指定set，就为空格，中间有其他间隔就停止截取
7、NCHR(n) 相当于 CHR(n USINGNCHAR_CS)
8、NLS_INITCAP(ch,nlspara)针对字符串单词首字母大写，其余小写，可以指定排序规则nlspara，，也可以不指定采用默认规则
9、NLS_LOWER(ch, nlspara)将字符串转换为小写字母，可以指定排序规则
10、NLS_UPPER(ch, nlspara)将字符串转换为大写字母，可以指定排序规则
11、NLSSORT(ch, nlspara)返回字符串的字节码。用于排序
12、REGEXP_REPLACE(ch_source,pattern)正则表达式替换
13、REGEXP_SUBSTR(ch_source,pattern)正则表达式截取
14、REPLACE(ch,search_string,replace_string)字符串替换
15、RPAD(expr1,n,expr2) 从expr1中截取n个字符返回，如果长度不够就用expr2填充右边，默认填补空格
16、RTRIM(ch,set) 将字符串ch右边的包含在set中的字符移除，如股票不指定set，就为空格，中间有其他间隔就停止截取
17、SOUNDEX(ch) 返回字符串参数的语音表示形式，相对于比较一些读音相同，但是拼写不同的单词是非常有用的，在中文环境中没多大用处
18、SUBSTR(ch,position,length)截取字符串
19、TRANSLATE(ch,from_string,to_string)与REPLACE函数功能类似
针对ch字符串，将from_string中的字符串一一替换为to_string
20、TREAT
21、TRIM(ch fromsource_string) 去掉两边ch
TRIM(LEADINGch fromsource_string) 去掉左边ch
TRIM(TRAILINGch fromsource_string) 去掉右边ch
TRIM(BOTHch fromsource_string) 去掉两边 ch
22、UPPER(ch) 字符转换为大写
字符函数返回数值
1、ASCII(ch) 返回字符的ASCII码，ch可以是CHAR,VARCHAR2, NCHAR, or NVARCHAR2
2、INSTR(source,ch,position,n)在source中从位置position开始搜索ch，第n次出现的位置，没有匹配的返回0，默认从1开始第一次出现
3、LENGTH(ch) 返回字符串长度
4、REGEXP_COUNT(source_string,pattern,position,match_para)
正则表达式规则匹配字符串在原字符串中出现的次数
5、REGEXP_INSTR(source_string,pattern)正则表达式匹配字符串位置
NLS字符函数
1、NLS_CHARSET_DECL_LEN(byte_count,char_set_id)
返回一个 NCHAR 列的声明长度（也就是字符个数）。byte_count 参数是列的宽度。'char_set_id' 参数是字符集 ID
2、NLS_CHARSET_ID(string)返回字符集名称 对应的字符集ID
3、NLS_CHARSET_NAME(number)返回字符集 ID对应的字符集名称
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