oracle中replace函数：
用法：replace(tarString,paString,gString)。
参数说明：tarString，要替换的原字符串；paString，需要替换的子字符串；gString，需要替换的目标字符串。
具体说明：
select replace('01111','0','2') from dual;结果是 21111若减少gString参数，即为将tarString中为paString的地方删除。具体说明：
select replace('01111','0') from dual;结果为 1111 oracle中regexp_replace函数：
转自http://blog.csdn.net/itmyhome1990/article/details/50380718
转自http://blog.csdn.net/itmyhome1990/article/details/50380718
转自http://blog.csdn.net/itmyhome1990/article/details/50380718
重要的事情说三遍。
REGEXP_REPLACE让你搜索的字符串的正则表达式模式REPLACE函数的功能。默认情况下，
该函数返回source_char与replace_string取代了正则表达式模式的每个实例。
返回的字符串是在相同的字符集source_char。
Oracle数据库中的REGEXP_REPLACE函数的语法是：
REGEXP_REPLACE(source_char, pattern [, replace_string [, position [, occurrence [, match_parameter ] ] ] ] ) 1 1搜索值的字符表达式。这通常是一个字符列，可以是任何数据类型CHAR，VARCHAR2，NCHAR，NVARCHAR2，CLOB或NCLOB。
正则表达式
Value Description ^ Matches the beginning of a string. If used with a match_parameter of ‘m’, it matches the start of a line anywhere within expression. $ Matches the end of a string. If used with a match_parameter of ‘m’, it matches the end of a line anywhere within expression. * 匹配零个或多个. + 匹配一个或多个出现. ? 匹配零次或一次出现. . 匹配任何字符，除了空. | Used like an "OR" to specify more than one alternative. [ ] Used to specify a matching list where you are trying to match any one of the characters in the list. [^ ] Used to specify a nonmatching list where you are trying to match any character except for the ones in the list. ( ) Used to group expressions as a subexpression. {m} Matches m times. {m,} Matches at least m times. {m,n} Matches at least m times, but no more than n times. \n n is a number between 1 and 9. Matches the nth subexpression found within ( ) before encountering \n. [..] Matches one collation element that can be more than one character. [::] Matches character classes. [==] Matches equivalence classes. \d 匹配一个数字字符. \D 匹配一个非数字字符. \w 匹配包括下划线的任何单词字符. \W 匹配任何非单词字符. \s 匹配任何空白字符，包括空格、制表符、换页符等等. \S 匹配任何非空白字符. \A Matches the beginning of a string or matches at the end of a string before a newline character. \Z Matches at the end of a string. *? Matches the preceding pattern zero or more occurrences. +? Matches the preceding pattern one or more occurrences. ?? Matches the preceding pattern zero or one occurrence. {n}? Matches the preceding pattern n times. {n,}? Matches the preceding pattern at least n times. {n,m}? Matches the preceding pattern at least n times, but not more than m times.可选。匹配的模式将被替换replace_string字符串。如果省略replace_string参数，
将删除所有匹配的模式，并返回结果字符串。
可选。在字符串中的开始位置搜索。如果省略，则默认为1。
可选。是一个非负整数默认为1，指示替换操作的发生：
如果指定0，那么所有出现将被替换字符串。
如果指定了正整数n，那么将替换第n次出现。
可选。它允许你修改REGEXP_REPLACE功能匹配的行为。它可以是以下的组合：
Value Description ‘c’ 区分大小写的匹配. ‘i’ 不区分大小写的匹配. ‘n’ Allows the period character (.) to match the newline character. By default, the period is a wildcard. ‘m’ expression is assumed to have multiple lines, where ^ is the start of a line and $ is the end of a line, regardless of the position of those characters in expression. By default, expression is assumed to be a single line. ‘x’ Whitespace characters are ignored. By default, whitespace characters are matched like any other character.让我们开始使用REGEXP_REPLACE函数替换字符串中的第一个字。
For example:
SELECT REGEXP_REPLACE ('itmyhome is my network id', '^(\S*)', 'luck') FROM dual; Result: luck is my network id 1234 1234这个例子会返回”luck is my network id”，
因为它会再字符串的开始找到第一个匹配的字符，然后替换为”luck”
我们将使用REGEXP_REPLACE函数来匹配单个数字字符模式。
For example:
SELECT REGEXP_REPLACE ('2, 5, and 10 are numbers in this example', '\d', '#') FROM dual; Result: '#, #, and ## are numbers in this example' 1234 1234此示例将所指定的\d数字将以#字符替换
我们可以改变我们的正则模式来搜索仅两位数字。
For example:
SELECT REGEXP_REPLACE ('2, 5, and 10 are numbers in this example', '(\d)(\d)', '#') FROM dual; Result: '2, 5, and # are numbers in this example' 1234 1234这个例子将替换具有两个数字并排指定的(\d)(\d)模式。在这种情况下，它将跳过2和5个数字值和用#字符替换10。
还有一个问题：就是同replace，只有前两个参数是什么意思
具体说明
select regexp_replace('01111','^0') from dual; 结果是 1111含义同replace函数。