问题
Why is the following instruction returning FALSE?
SELECT '[1-3]{5}' SIMILAR TO '22222' ;
I can't find what is wrong with that, according to the Postgres doc ...
回答1:
The operator is defined as:
string SIMILAR TO pattern
so the first parameter is the string that you want to compare. The second parameter is the regex to compare against.
You need:
SELECT '22222' SIMILAR TO '[1-3]{5}';
回答2:
try
SELECT '22222' ~ '[1-3]{5}'
SIMILAR is not POSIX standard
The SIMILAR TO operator returns true or false depending on whether its pattern matches the given string. It is similar to LIKE, except that it interprets the pattern using the SQL standard's definition of a regular expression. SQL regular expressions are a curious cross between LIKE notation and common regular expression notation.
...
POSIX regular expressions provide a more powerful means for pattern matching than the LIKE and SIMILAR TO operators. Many Unix tools such as egrep, sed, or awk use a pattern matching language that is similar to the one described here.
http://www.postgresql.org/docs/9.2/static/functions-matching.html#FUNCTIONS-POSIX-REGEXP
回答3:
Your basic error has already been answered.
More importantly, don't use SIMILAR TO at all. It's completely pointless:
- Query performance in PostgreSQL using 'similar to'
- Difference between LIKE and ~ in Postgres
Use LIKE or regular expression match ~ or other pattern matching operators:
- Pattern matching with LIKE, SIMILAR TO or regular expressions in PostgreSQL
For 5 digits between 1 and 3 use the expression @Thomas provided.
If you actually want 5 identical digits between 1 and 3 like your example suggests I suggest a back reference:
SELECT '22222' ~ '([1-9])\1{4}'
Related answer with more explanation:
Deleting records with number repeating more than 5
SQL Fiddle demonstrating both.
来源：https://stackoverflow.com/questions/24656452/using-similar-to-for-a-regex