REGEXP_COUNT

Syntax

Description of the illustration regexp_count.gif

Purpose

REGEXP_COUNT complements the functionality of the REGEXP_INSTR function by returning the number of times a pattern occurs in a source string. The function evaluates strings using characters as defined by the input character set. It returns an integer indicating the number of occurrences of pattern. If no match is found, then the function returns 0.

• source_char is a character expression that serves as the search value. It is commonly a character column and can be of any of the datatypes CHAR, VARCHAR2, NCHAR, NVARCHAR2, CLOB, or NCLOB.

• pattern is the regular expression. It is usually a text literal and can be of any of the datatypes CHAR, VARCHAR2, NCHAR, or NVARCHAR2. It can contain up to 512 bytes. If the datatype of pattern is different from the datatype of source_char, then Oracle Database converts pattern to the datatype of source_char.

  REGEXP_COUNT ignores subexpression parentheses in pattern. For example, the pattern '(123(45))' is equivalent to '12345'. For a listing of the operators you can specify in pattern, refer to Appendix C, "Oracle Regular Expression Support".

• position is a positive integer indicating the character of source_char where Oracle should begin the search. The default is 1, meaning that Oracle begins the search at the first character of source_char. After finding the first occurrence of pattern, the database searches for a second occurrence beginning with the first character following the first occurrence.

• match_param is a text literal that lets you change the default matching behavior of the function. You can specify one or more of the following values for match_param:

  • 'i' specifies case-insensitive matching.

  • 'c' specifies case-sensitive matching.

  • 'n' allows the period (.), which is the match-any-character character, to match the newline character. If you omit this parameter, then the period does not match the newline character.

  • 'm' treats the source string as multiple lines. Oracle interprets the caret (^) and dollar sign ($) as the start and end, respectively, of any line anywhere in the source string, rather than only at the start or end of the entire source string. If you omit this parameter, then Oracle treats the source string as a single line.

  • 'x' ignores whitespace characters. By default, whitespace characters match themselves.

  If you specify multiple contradictory values, then Oracle uses the last value. For example, if you specify 'ic', then Oracle uses case-sensitive matching. If you specify a character other than those shown above, then Oracle returns an error.

  If you omit match_param, then:

  • The default case sensitivity is determined by the value of the NLS_SORT parameter.

  • A period (.) does not match the newline character.

  • The source string is treated as a single line.

Examples

The following example shows that subexpressions parentheses in pattern are ignored:

SELECT REGEXP_COUNT('123123123123123', '(12)3', 1, 'i') REGEXP_COUNT
   FROM DUAL;
 
REGEXP_COUNT
------------
           5

In the following example, the function begins to evaluate the source string at the third character, so skips over the first occurrence of pattern:

SELECT REGEXP_COUNT('123123123123', '123', 3, 'i') COUNT FROM DUAL; 

     COUNT
----------
         3