Querying data with letters in Oracle [regular expressions]

1,regexp_like: Similar to the function of like
2,REGEXP_INSTR: Similar to the function of INSTR
3,REGEXP_SUBSTR: Similar to the function of SUBSTR
4,regexp_replace: Similar to the function of REPLACE
They are used in the same way as Oracle SQL functions like, INSTR, SUBSTR, and replace usages.
However, they use POSIX regular expressions instead of the old percent (%) and wildcard character (_) characters.
POSIX Regular expressions are composed of standard metacharacters (metacharacters):
' ^ ' matches the starting position of the input string, which is used in a square bracket expression, which indicates that the character set is not accepted.
' $ ' matches the end position of the input string. If the Multiline property of the RegExp object is set, the $ is also
With '/n ' or '/R '.
'. ' matches any single character except for a newline character.
'? ' matches the preceding subexpression 0 or one time.
' + ' matches the preceding sub-expression one or more times.
' * ' matches the preceding subexpression 0 or more times.
' | ' indicates a choice between the two items. Example ' ^ ([a-z]+|[ 0-9]+) $ ' denotes all lowercase letters or numbers combined into a
String.
' () ' marks the start and end position of a subexpression.
' [] ' marks a bracket expression.
' {m,n} ' an exact occurrence of the frequency range,m=< occurrences <=n, ' {m} ' indicates the presence of M times, ' {m,} ' means at least
Appears m times.
/num matches num, where num is a positive integer. A reference to the obtained match.
Character clusters:
[[: Alpha:]] any letter.
[[:d Igit:]] any number.
[[: Alnum:]] Any letters and numbers.
[[: Space:]] any whitespace character.
[[: Upper:]] any uppercase letters.
[[: Lower:]] any lowercase letter.
[[:p UNCT:]] any punctuation.
[[: Xdigit:]] Any 16 binary number, equivalent to [0-9a-fa-f].
Operator precedence for various operators
/Escape character
(), (?:), (? =), [] parentheses and square brackets
*, +,?, {n}, {n,}, {n,m} qualifier
^, $, anymetacharacter position and order

How to use:
SelectDabh fromQTYWBwhereRegexp_like (Dabh,'[[: Alpha:]]');

Querying data with letters in Oracle [regular expressions]