[REGEX] :: POSIX ERE Meta Character '' 9. + ( plus ) ''

POSIX ERE( Extended Regular Expression )

9. +
10. ?
11. |

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9. + ( Plus )

구문 ( Syntax )

<plus> ::= +

• 사용 예

  <pattern_expr><plus>
  

설명 ( Description )

• 1 or MORE
• 수량자(quantifier)로, <plus> 앞의 <pattern_expr>이 하나 이상 있음을 의미한다.
  • ex) a+ => a, aa, aaa, ...
• <plus>만 있는 경우
  • ex) +
  • 결과
    • Oracle : zero-length match
    • PostgreSQL, MySQL, MariaDB : error 처리

• 다른 수량자들과는 달리 zero-length match가 발생하지 않는다.
  • Oracle은 예외적으로 empty string에 대한 +도 zero-length match가 발생한다.
    • ex) +

예제 ( Examples )

SQL> SELECT REGEXP_SUBSTR( 'aaaaabbb', 'a+' ) AS RESULT FROM DUAL;

RESULT
--------------------
aaaaa

SQL> SELECT REGEXP_SUBSTR( 'abababc', '(ab)+' ) AS RESULT FROM DUAL;

RESULT
--------------------
ababab

SQL> SELECT REGEXP_SUBSTR( 'knight', '.+knight' ) AS RESULT FROM DUAL;

RESULT
--------------------
NULL

SQL> SELECT REGEXP_SUBSTR( 'GOLDILOCKS', 'GOLD(.+)' ) AS RESULT FROM DUAL;

RESULT
--------------------
GOLDILOCKS

• <plus>만 있는 경우

  < Oracle >
  SQL> SELECT REGEXP_SUBSTR( 'ab', '+' ) AS RESULT FROM DUAL;
  
  RESULT
  ------------------------------
  NULL
  
  SQL> SELECT REGEXP_COUNT( 'ab', '+' ) AS RESULT FROM DUAL;
  
      RESULT
  ----------
           3
  
  
  < PostgreSQL >
  postgres=# SELECT REGEXP_MATCHES( 'ab', '+', 'g' ) AS RESULT;
  ERROR:  invalid regular expression: quantifier operand invalid
  
  
  < MySQL >
  mysql> SELECT REGEXP_SUBSTR( 'ab', '+' ) AS RESULT;
  ERROR 3688 (HY000): Syntax error in regular expression on line 1, character 1.
  
  
  < MariaDB >
  MariaDB [test]> SELECT REGEXP_SUBSTR( 'ab', '+' ) AS RESULT;
  ERROR 1139 (42000): Got error 'nothing to repeat at offset 0' from regexp
  
  

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