The regular expressions in MaxCompute SQL use the PCRE standard, matched by characters. The meta character to be supported is as follows:
Metacharacter Description
^ Top of line (TOL)
$ End of line
. Any character
* Matches for zero or multiple times
+ Matches for once or multiple times
? Matches for zero time or once
? Matches modifier. When this character follows any other constraints (*, +,? {n}, {n, {n, m},},  the match mode is non greedy.  Non greedy mode matches strings as little as possible,  while the default greedy mode matches strings as more as possible.
A | B A or B
(abc)* Matches ‘abc’ for zero or multiple times
{n} or {m, n} Matching times
[ab] Matches any character in the brackets. In the example, it is to match a or b.
[a-d] Matches any character in a, b, c, and d.
[^ab] ^ indicats ‘non’, to match any character which is not a and b.
[::] See POSIX character group in next table.
\ Escape character
\n N is a digit from 1 to 9 and is backward referenced.
\d digits
\ D Non-number
POSIX character group:
POSIX Character Group Description Range
[[:alnum:]] letter and digit characters [a-zA-Z0-9]
[[:alpha:]] letter [a-zA-Z]
[[:ascii:]] ASCII character [\x00-\x7F]
[[:blank:]] Space character and tabs [ \t]
[[:cntrl:]] Control character [\x00-\x1F\x7F]
[[:digit:]] Digit character [0-9]
[[:graph:]] Characters except white space characters [\x21-\x7E]
[[:lower:]] Lowercase characters [a-z]
[[:print:]] [:graph:] and white space characters [\x20-\x7E]
[[:punct:]] punctuation [][!” [][!”#$%&’()*+,./:;<=>? @\^_`{|}~-]
[[:space:]] White space characters [ \t\r\n\v\f]
[[:upper:]] Uppercase characters [A-Z]
[[:xdigit:]] hexadecimal character [A-Fa-f0-9]

Because the system uses a backslash () as an escape character, all “\” which appear in the regular expression pattern perform two escapes. For example, the regular expression needs to match the string “a+b”. The “+” is a special character in regular expressions and must be expressed by escape. The expression in a regular engine is “a\+b”, because the system needs to explain a layer of escape, the expression which can match this string is “a\\+b”. 

Suppose that the table test_dual is:
select 'a+b' rlike 'a\\\+b' from test_dual;

| _c1 |

| true |
In extreme cases, to match the character “ \”,  because “ \” is a special character in a regular engine, it needs to be expressed by “\”, while the system does an escape for it again, it is written as “\\”.
select 'a\\b', 'a\\b' rlike 'a\\\\b' from test_dual;

| _c0 | _c1 |

| a\b | true |
Note
To write  a\\b in MaxCompute SQL, and the output result is a\b.
If TAB exists in a string, when the system reads these two characters \t, they are already saved as one character by the system. Therefore, in regular expression, it is a general character.
select 'a\tb', 'a\tb' rlike 'a\tb' from test_dual;| _c0 | _c1 |

| a b | true |