使用REGEXP_COUNT函数统计字符串出现的次数

在Oracle的11g版本中引入了REGEXP_COUNT函数，使用这个函数可以统计字符串出现的次数，小观一下。


1.REGEXP_COUNT函数语法参考
REGEXP_COUNT (source_char, pattern [, position [, match_param]])


2.先看一下使用最少参数的效果（仅使用前两个参数）
1）得到字符串中小写字母“a”的出现次数
sys@ora11g> select regexp_count ('The pro-niece was born today, so exciting.', 'a') "Count 'a'" from dual;


Count 'a'
----------
         2


sys@ora11g> select regexp_count ('THE PRO-NIECE WAS BORN TODAY, SO EXCITING!', 'a') "Count 'a'" from dual;


Count 'a'
----------
         0


3.大小写敏感匹配
不加其余参数的情况下，等同于下面的全参数形式。表示对字母大小写敏感匹配（最后一个参数“c”表示大小写敏感）。
sys@ora11g> select regexp_count ('The pro-niece was born today, so exciting.', 'a', 1, 'c') "Count 'a' case-sensitive" from dual;


Count 'a' case-sensitive
------------------------
                       2


sys@ora11g> select regexp_count ('THE PRO-NIECE WAS BORN TODAY, SO EXCITING!', 'a', 1, 'c') "Count 'a' case-sensitive" from dual;


Count 'a' case-sensitive
------------------------
                       0


4.大小写不敏感匹配
若意欲同时匹配大写字母“A”和小写字母“a”，可以启用“i”参数，表示大小写不敏感。
sys@ora11g> select regexp_count ('The pro-niece was born today, so exciting.', 'a', 1, 'i') "Count 'a' case-insensitive" from dual;


Count 'a' case-insensitive
--------------------------
                         2


sys@ora11g> select regexp_count ('THE PRO-NIECE WAS BORN TODAY, SO EXCITING!', 'a', 1, 'i') "Count 'a' case-insensitive" from dual;


Count 'a' case-insensitive
--------------------------
                         2


5.从指定位置进行检索
倒数第二个参数表示开始检索关键字的位置，如下例中的17表示从字符串的第17个字符处开始检索字母a（不区分大小写）。
sys@ora11g> select regexp_count ('The pro-niece was born today, so exciting!', 'a', 17, 'i') "Count 'a'"  from dual;


Count 'a'
----------
         1