Oracle10g Regular Expression （Oracle正则表达式）

Oracle10g Regular ExpressionSubmitted by Sarvindu on Tue, 2009-10-20 04:55

• SQL & PL/SQL

Oracle10g Regular Expression

Oracle database 10g added a new feature "Regular Expression" enhancement that can be used with SQL and PL/SQL statements.

There are four regular expression functions :-

REGEXP_LIKE
REGEXP_SUBSTR
REGEXP_INSTR
REGEXP_REPLACE

The functions REGEXP_SUBSTR, REGEXP_INSTR and REGEXP_REPLACE basically extend the functionality of other well known string functions SUBSTR, INSTR and REPLACE.

REGEXP_LIKE is basically an operator that is similar to existing LIKE operator.

The above regular expression functions are very efficient and powerful.

A regular expression is basically the combination of one or more literals with some metacharacters , this is used for pattern matching.

Oracle Regular Expression functions support the POSIX (Portable Operating System Interface) standard character classes.

Metacharacter and Character Class Description

* match 0 or more times
+ match 1 or more times
? match 0 or 1 time
^ start of the expression
$ end of the the expression
{m} match exactly m times
{m,} match at least m times
{m, n} match at least m times but no more than n times
| alternate operator
( ) group used for subexpression and backreferencing
[char] character List (can be used as literals except ^ ,- and character class)
\digit backslash followed by a digit between 1 and 9 ,used for backrerencing the respective subexpression.
[:alpha:] alphabetic characters
[:lower:] lowercase alphabetic characters
[:upper:] uppercase alphabetic characters
[:digit:] numeric digits
[:alnum:] alphanumeric characters
[:space:] nonprinting space characters e.g. carriage return, newline, vertical tab, and form feed
[:punct:] punctuation characters
[:cntrl:] nonprinting control characters
[:print:] printable characters

Matching Modes

i case insensitive matching
c case sensitive matching
n the dot match any character, including newlines.
m the caret and dollar match at the start and end of each line

REGEXP_LIKE
==============
Syntax : REGEXP_LIKE(source_string, pattern [, match_parameter])

source_string can be any character expression and will be used as search value.
pattern is any valid regular expression.
match_parameter can be one or more combination of valid Matching Modes ('i','c','n','m').

Example : To find the list of Product Codes that contain any non-numric chracters.

create table t_product
(
product_id number,
product_code varchar2(10),
product_desc varchar2(100)
);

insert into t_product values (1,'10','Option1');
insert into t_product values (2,'20','Option2');
insert into t_product values (3,'30','Option3');
insert into t_product values (4,'40a','Option4');
insert into t_product values (5,'Z50','Option5');

select product_code from t_product
where regexp_like(product_code, '[^[:digit:]]');

The query output in this case would be :

PRODUCT_CODE
40a
Z50

REGEXP_SUBSTR
==============
Syntax : REGEXP_SUBSTR(source_string, pattern [, position [, occurrence [, match_parameter ]]])

REGEXP_SUBSTR returns the substring for a regular expression pattern.
source_string is search value
pattern is a valid regular expression
position is an integer n (n >0) that indicates the position from where serach should begin (default is 1)
occurrence is an integer n (n >0) that indicates the search for which occurrence of pattern in source_string.
match_parameter can be one or more combination of valid Matching Modes ('i','c','n','m').

Example : To find the first value from the set of values separated by commas

SELECT REGEXP_SUBSTR('P1,P2,P3','[^,]+') FROM DUAL;

The query output in this case will be P1

REGEXP_INSTR
============
Syntax : REGEXP_INSTR (source_string, pattern [, position [, occurrence [, return_option [, match_parameter ]]]])

REGEXP_INSTR returns the position of the matched substring.In case no match , the function returns 0.

source_string is search value
pattern is a valid regular expression
position is an integer n (n >0) that indicates the position from where serach should begin (default is 1)
occurrence is an integer n (n >0) that indicates the search for which occurrence of pattern in source_string.
return_option gives the position w.r.t. occurrence, for value 0 => returns the position of the first character of the occurrence , for value 1 => returns the position of the character following the occurrence
match_parameter can be one or more combination of valid Matching Modes ('i','c','n','m').
Example :
select REGEXP_INSTR('The Sum is 100.','[[:digit:]]+') FROM DUAL;
This query will return 12, the starting position of 100 in the string.

REGEXP_REPLACE
===============
Syntax : REGEXP_REPLACE(source_char, pattern [, replace_string [, position [, occurrence [, match_parameter ]]]])

REGEXP_REPLACE returns source_char by replacing any matched substring for a regular expression pattern.
source_char is search value
pattern is a valid regular expression
replace_string is a character string used for replacement this can be used as backreferences to subexpressions in the form \n where n is 1 to 9.
position is an integer n (n >0) that indicates the position from where serach should begin (default is 1)
occurrence is an integer n (n >0) that indicates the occurrence of replace operation, for value 0 => replace all the occurrences of the matched substring , for value n => replaces the nth occurrence.
match_parameter can be one or more combination of valid Matching Modes ('i','c','n','m','x')
Example :
SELECT REGEXP_REPLACE('This is an example with lot blank spaces','( ){2,}', ' ') FROM DUAL;
This query will return "This is an example with lot blank spaces" , this will replace each occurrence of two or more spaces with a single space.