记忆在这里化作永恒

SQL Element     Category    Description
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REGEXP_LIKE     Condition   Searches a character column for a pattern. 
                            Use this function in the WHERE clause of a query to return rows matching a regular expression. 
                            The condition is also valid in a constraint or as a PL/SQL function returning a boolean.
                            The following WHERE clause filters employees with a first name of Steven or Stephen:
                            WHERE REGEXP_LIKE(first_name, '^Ste(v|ph)en$')
 
REGEXP_REPLACE  Function    Searches for a pattern in a character column and replaces each occurrence of that pattern with the specified string.
                            The following function call puts a space after each character in the country_name column:
                            REGEXP_REPLACE(country_name, '(.)', '\1 ')
 
REGEXP_INSTR    Function    Searches a string or substring for a given occurrence of a regular expression pattern (a substring) 
                            and returns an integer indicating the position in the string or substring where the match is found.
                            You specify which occurrence you want to find and the start position.
                            The following function call performs a boolean test for a valid email address in the email column:
                            REGEXP_INSTR(email, '\w+@\w+(\.\w+)+') > 0
 
REGEXP_SUBSTR   Function    Searches a string or substring for a given occurrence of a regular expression pattern (a substring) 
                            and returns the substring itself.You specify which occurrence you want to find and the start position.
                            The following function call uses the x flag to match the first string by ignoring spaces in the regular expression:
                            REGEXP_SUBSTR('oracle', 'o r a c l e', 1, 1, 'x')
 
REGEXP_COUNT    Function    Returns the number of times a pattern appears in a string. You specify the string and the pattern.
                            You can also specify the start position and matching options (for example, c for case sensitivity).
                            The following function call returns the number of times that e (but not E) appears in the string 'Albert Einstein', 
                            starting at character position 7 (that is, one):
                            REGEXP_COUNT('Albert Einstein', 'e', 7, 'c')