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11. using regular expressions with oracle database

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Amrit Kaur
Amrit Kaur

The Oracle database provides a set of SQL functions to search and manipulate strings using regular expressions. These functions include REGEXP_COUNT, REGEXP_LIKE, REGEXP_SUBSTR, REGEXP_INSTR, and REGEXP_REPLACE. Regular expressions use metacharacters like period, plus, star, and pipe to specify patterns to match. Metacharacters have special meanings like wildcard, repeating, or range of characters. The regular expression functions take a source string and pattern to perform matching and extraction.

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Using Regular Expressions With Oracle Database
• The database provides a set of SQL functions that allow you to search and manipulate strings using regular expressions. • Apply on datatype that holds character data .
• A regular expression is specified using two types of characters: – Meta characters • operators that specify algorithms – Literals • the actual characters to search for.
SQL Regular Expression Function Returns the number of times a pattern match is found in an input sting REGEXP_COUNT Similar to the LIKE operator, but performs regular expression matching instead of simple pattern matching (condition) REGEXP_LIKE REGEXP_SUBSTR REGEXP_INSTR REGEXP_REPLACE Searches for a regular expression pattern and replaces it with a replacement string Searches for a regular expression pattern within a given string and extracts the matched substring Searches a string for a regular expression pattern and returns the position where the match is found DescriptionFunction or Condition Name
What are Metacharacters? • Metacharacters are special characters that have a special meaning such as – a wildcard, – a repeating character, – a nonmatching character, – or a range of characters. • You can use several predefined metacharacter symbols in the pattern matching.
Using Metacharacters Metacharcater Operator Name Description . Any Character -- Dot Matches any character + One or More -- Plus Quantifier Matches one or more occurrences of the preceding subexpression ? Zero or One -- Question Mark Quantifier Matches zero or one occurrence of the preceding subexpression * Zero or More -- Star Quantifier Matches zero or more occurrences of the preceding subexpression {m} Interval--Exact Count Matches exactlym occurrences of the preceding subexpression {m,} Interval--At Least Count Matches at least m occurrences of the preceding subexpression {m,n} Interval--Between Count Matches at least m, but not more than n occurrences of the preceding subexpression [ ... ] Matching Character List Matches any character in list ... [^ ... ] Non-Matching Character List Matches any character not in list ...
Using Metacharacters Metacharcater Operator Name Description | Or 'a|b' matches character 'a' or 'b'. ( ... ) Subexpression or Grouping Treat expression ... as a unit. The subexpression can be a string of literals or a complex expression containing operators. n Backreference Matches the nth preceding subexpression, where n is an integer from 1 to 9. Escape Character Treat the subsequent metacharacter in the expression as a literal. ^ Beginning of Line Anchor Match the subsequent expression only when it occurs at the beginning of a line. $ End of Line Anchor Match the preceding expression only when it occurs at the end of a line.
Regular Expression Function Syntax REGEXP_LIKE (source_char, pattern [,match_option] REGEXP_INSTR (source_char, pattern [, position [, occurrence [, return_option [, match_option [, subexpr]]]]]) REGEXP_SUBSTR (source_char, pattern [, position [, occurrence [, match_option [, subexpr]]]]) REGEXP_REPLACE(source_char, pattern [,replacestr [, position [, occurrence [, match_option]]]]) REGEXP_COUNT (source_char, pattern [, position [, occurrence [, match_option]]])
Regular Expression Function Syntax • match_options is a text literal that lets you change the default matching behavior of the function. – 'i' specifies case-insensitive matching. – 'c' specifies case-sensitive matching. – 'n' allows the period (.), to match the newline character. – 'm' treats the source string as multiple lines
Examples • Display details of employees whose first name is Steven or Stephen (where first_name begins with Ste and ends with en and in between is either v or ph) SELECT first_name, last_name FROM employees WHERE REGEXP_LIKE (first_name, '^Ste(v|ph)en$'); • Last name for those employees with a double vowel in their last name SELECT last_name FROM employees WHERE REGEXP_LIKE (last_name, '([aeiou])1', 'i');
Examples • examines phone_number, looking for the pattern xxx.xxx.xxxx. Oracle reformats this pattern with (xxx) xxx-xxxx. SELECT REGEXP_REPLACE(phone_number, '([[:digit:]]{3}).([[:digit:]]{3}).([[:digit:]]{4})‘, '(1) 2-3') "REGEXP_REPLACE“ FROM employees; • looking for http:// followed by a substring of one or more alphanumeric characters and optionally, a period (.). SELECT REGEXP_SUBSTR('http://www.oracle.com/products', 'http://([[:alnum:]]+.?){3,4}/?') "REGEXP_SUBSTR" FROM DUAL;

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11. using regular expressions with oracle database

  • 1. Using Regular Expressions With Oracle Database
  • 2. • The database provides a set of SQL functions that allow you to search and manipulate strings using regular expressions. • Apply on datatype that holds character data .
  • 3. • A regular expression is specified using two types of characters: – Meta characters • operators that specify algorithms – Literals • the actual characters to search for.
  • 4. SQL Regular Expression Function Returns the number of times a pattern match is found in an input sting REGEXP_COUNT Similar to the LIKE operator, but performs regular expression matching instead of simple pattern matching (condition) REGEXP_LIKE REGEXP_SUBSTR REGEXP_INSTR REGEXP_REPLACE Searches for a regular expression pattern and replaces it with a replacement string Searches for a regular expression pattern within a given string and extracts the matched substring Searches a string for a regular expression pattern and returns the position where the match is found DescriptionFunction or Condition Name
  • 5. What are Metacharacters? • Metacharacters are special characters that have a special meaning such as – a wildcard, – a repeating character, – a nonmatching character, – or a range of characters. • You can use several predefined metacharacter symbols in the pattern matching.
  • 6. Using Metacharacters Metacharcater Operator Name Description . Any Character -- Dot Matches any character + One or More -- Plus Quantifier Matches one or more occurrences of the preceding subexpression ? Zero or One -- Question Mark Quantifier Matches zero or one occurrence of the preceding subexpression * Zero or More -- Star Quantifier Matches zero or more occurrences of the preceding subexpression {m} Interval--Exact Count Matches exactlym occurrences of the preceding subexpression {m,} Interval--At Least Count Matches at least m occurrences of the preceding subexpression {m,n} Interval--Between Count Matches at least m, but not more than n occurrences of the preceding subexpression [ ... ] Matching Character List Matches any character in list ... [^ ... ] Non-Matching Character List Matches any character not in list ...
  • 7. Using Metacharacters Metacharcater Operator Name Description | Or 'a|b' matches character 'a' or 'b'. ( ... ) Subexpression or Grouping Treat expression ... as a unit. The subexpression can be a string of literals or a complex expression containing operators. n Backreference Matches the nth preceding subexpression, where n is an integer from 1 to 9. Escape Character Treat the subsequent metacharacter in the expression as a literal. ^ Beginning of Line Anchor Match the subsequent expression only when it occurs at the beginning of a line. $ End of Line Anchor Match the preceding expression only when it occurs at the end of a line.
  • 8. Regular Expression Function Syntax REGEXP_LIKE (source_char, pattern [,match_option] REGEXP_INSTR (source_char, pattern [, position [, occurrence [, return_option [, match_option [, subexpr]]]]]) REGEXP_SUBSTR (source_char, pattern [, position [, occurrence [, match_option [, subexpr]]]]) REGEXP_REPLACE(source_char, pattern [,replacestr [, position [, occurrence [, match_option]]]]) REGEXP_COUNT (source_char, pattern [, position [, occurrence [, match_option]]])
  • 9. Regular Expression Function Syntax • match_options is a text literal that lets you change the default matching behavior of the function. – 'i' specifies case-insensitive matching. – 'c' specifies case-sensitive matching. – 'n' allows the period (.), to match the newline character. – 'm' treats the source string as multiple lines
  • 10. Examples • Display details of employees whose first name is Steven or Stephen (where first_name begins with Ste and ends with en and in between is either v or ph) SELECT first_name, last_name FROM employees WHERE REGEXP_LIKE (first_name, '^Ste(v|ph)en$'); • Last name for those employees with a double vowel in their last name SELECT last_name FROM employees WHERE REGEXP_LIKE (last_name, '([aeiou])1', 'i');
  • 11. Examples • examines phone_number, looking for the pattern xxx.xxx.xxxx. Oracle reformats this pattern with (xxx) xxx-xxxx. SELECT REGEXP_REPLACE(phone_number, '([[:digit:]]{3}).([[:digit:]]{3}).([[:digit:]]{4})‘, '(1) 2-3') "REGEXP_REPLACE“ FROM employees; • looking for http:// followed by a substring of one or more alphanumeric characters and optionally, a period (.). SELECT REGEXP_SUBSTR('http://www.oracle.com/products', 'http://([[:alnum:]]+.?){3,4}/?') "REGEXP_SUBSTR" FROM DUAL;