DB2 Scalar functions - REGEXP_COUNT


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Desenvolvido por DORNELLES Carlos Alberto - Analista de Sistemas - Brasília DF. - cad_cobol@hotmail.com

REGEXP_COUNT

The REGEXP_COUNT scalar function returns a count of the number of times that a regular expression pattern is matched in a string.

REGEXP_COUNT(source-string ,pattern-expression ,start ,flags ,CODEUNITS32,CODEUNITS16OCTETS )

The schema is SYSIBM.

source-string
An expression that specifies the string in which the search is to take place.
This expression must return a built-in character string, graphic string, numeric value, Boolean value, or datetime value.
A numeric, Boolean, or datetime value is implicitly cast to VARCHAR before the function is evaluated.
A character string cannot specify the FOR BIT DATA attribute (SQLSTATE 42815).
pattern-expression
An expression that specifies the regular expression string that is the pattern for the search.
This expression must return a built-in character string, graphic string, numeric value, Boolean value, or datetime value.
A numeric, Boolean, or datetime value is implicitly cast to VARCHAR before the function is evaluated.
The length of a CLOB or DBCLOB expression must not be greater than the maximum length of a VARCHAR or VARGRAPHIC data type. A character string cannot specify the FOR BIT DATA attribute (SQLSTATE 42815).
start
An expression that specifies the position within source-string at which the search is to start.
The expression must return a built-in character string, graphic string, Boolean, or numeric value.
If the value is not of type INTEGER, it is implicitly cast to INTEGER before the function is evaluated.
The value of the integer must be greater than or equal to 1.
If OCTETS is specified and the source string is graphic data, the value of the integer must be odd (SQLSTATE 428GC).
The default start value is 1. See parameter description for CODEUNITS16, CODEUNITS32, or OCTETS for the string unit that applies to the start position.
flags
An expression that specifies flags that controls aspects of the pattern matching.
The expression must return a built-in character string that does not specify the FOR BIT DATA attribute (SQLSTATE 42815).
The string can include one or more valid flag values and the combination of flag values must be valid (SQLSTATE 2201T).
An empty string is the same as the value 'c'. The default flag value is 'c'.

Table 1. Supported flag values

Flag value Description
c Specifies that matching is case-sensitive.
This flag is the default value if 'c' or 'i' is not specified. This value must not be specified with a value of 'i'.
i Specifies that matching is case insensitive.
This value must not be specified with a value of 'c'.
m Specifies that the input data can contain more than one line.
By default, the '^' in a pattern matches only the start of the input string; the '$' in a pattern matches only the end of the input string.
If this flag is set, "^" and "$" also matches at the start and end of each line within the input string.
n Specifies that the '.' character in a pattern matches a line terminator in the input string. By default, the '.' character in a pattern does not match a line terminator.
A carriage-return and line-feed pair in the input string behaves as a single-line terminator, and matches a single "." in a pattern.
s Specifies that the '.' character in a pattern matches a line terminator in the input string. This value is a synonym for the 'n' value.
x Specifies that white space characters in a pattern are ignored, unless escaped.

CODEUNITS16, CODEUNITS32, or OCTETS
Specifies the string unit of the start value:
  • CODEUNITS16 specifies that the start value is expressed in 16-bit UTF-16 code units.
  • CODEUNITS32 specifies that the start value is expressed in 32-bit UTF-32 code units. This is the default.
  • OCTETS specifies that the start value is expressed in bytes.

If the string unit is specified as CODEUNITS16 or OCTETS, and if the string unit of the source string is CODEUNITS32, an error is returned (SQLSTATE 428GC).

For more information, see "String units in built-in functions" in Character strings.

Result

The result of the function is an INTEGER that represents the number of occurrences of the pattern expression within the source string.
If the pattern expression is not found and no argument is null, the result is 0.

If any argument of the REGEXP_COUNT function can be null, the result can be null.
If any argument is null, the result is the null value.

Notes

  • The regular expression processing is done by using the International Components for Unicode (ICU) regular expression interface.
  • Considerations for non-Unicode databases:
    • A regular expression pattern supports only halfwidth control characters; use a character string data type for the pattern expression argument.
      A character string data type can be used for the pattern expression argument even when a graphic string data type is used for the source string argument.
    • The source string argument must be a graphic string data type if the pattern expression argument is a graphic string data type.

Example

Count the number of times "Steven" or "Stephen" occurs in the string "Steven Jones and Stephen Smith are the best players". 

   SELECT REGEXP_COUNT('Steven Jones and Stephen Smith are the best players', 'Ste(v|ph)en') 
   FROM   sysibm.sysdummy1
The result is 2.

© Copyright IBM Corp.