Обсуждение: DIFFERENCE BETWEEN LIKE AND SIMILAR OPERATORS

JORGE MALDONADO wrote:
> I've been reading PostgreSQL documentation and I do not really understand
> the difference between LIKE and SIMILAR operators. Can someone explain?

SIMILAR is a super-set of LIKE syntax.  Our docs have:

    http://developer.postgresql.org/pgdocs/postgres/functions-matching.html#FUNCTIONS-SIMILARTO-REGEXP

    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.

For the super-set, see the bullets below this line:

     In addition to these facilities borrowed from LIKE, SIMILAR TO
    supports these pattern-matching metacharacters borrowed from POSIX
    regular expressions:

--
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  PG East:  http://www.enterprisedb.com/community/nav-pg-east-2010.do

"Standard" regular expressions are extremely well supported in
Postgres and are one of the main reasons I use Postgres.  I strongly,
very strongly, recommend plunging into regular expressions as deeply
as you can.  Once you start using them "regularly" you will be unable
to live without them.  They are built into the Vim editor which is
also a must have.  Like regular expressions, once you have used Vim
for awhile, you absolutely can't go back.

John

On Mar 16, 2010, at 2:31 AM, Bruce Momjian wrote:

> JORGE MALDONADO wrote:
>> I've been reading PostgreSQL documentation and I do not really
>> understand
>> the difference between LIKE and SIMILAR operators. Can someone
>> explain?
>
> SIMILAR is a super-set of LIKE syntax.  Our docs have:
>
>     http://developer.postgresql.org/pgdocs/postgres/functions-matching.html#FUNCTIONS-SIMILARTO-REGEXP
>
>     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.
>
> For the super-set, see the bullets below this line:
>
>      In addition to these facilities borrowed from LIKE, SIMILAR TO
>     supports these pattern-matching metacharacters borrowed from POSIX
>     regular expressions:
>
> --
>  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
>  EnterpriseDB                             http://enterprisedb.com
>
>  PG East:  http://www.enterprisedb.com/community/nav-pg-east-2010.do
>
> --
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