{n} or {m,n} notation matches many occurrences of the previous atom (or "piece") of the pattern.
m and n are integers.
a*: Can be written as a{0,}.
a+: Can be written as a{1,}.
a?: Can be written as a{0,1}.
a{n} matches exactly n instances of a.
a{n,} matches n or more instances of a.
a{m,n} matches m through n instances of a, inclusive.
m and n must be in the range from 0 to RE_DUP_MAX (default 255), inclusive.
If both m and n are given, m must be less than or equal to n.
mysql>
mysql> SELECT 'abcde' REGEXP 'a[bcd]{2}e';
+-----------------------------+
| 'abcde' REGEXP 'a[bcd]{2}e' |
+-----------------------------+
| 0 |
+-----------------------------+
1 row in set (0.01 sec)