= or LIKE ?

Hi.

Can anyone explain me this behavior?

testdb=# select E'\\' = E'\\';
?column?
----------
t
(1 row)

testdb=# select E'\\' like E'\\';
?column?
----------
f
(1 row)

Shouldnt the like operator do the same as the = if there occours no
wildcards and stuff in the string?

--
Jesper

Jesper Krogh <jesper(at)krogh(dot)cc> writes:
> Shouldnt the like operator do the same as the = if there occours no
> wildcards and stuff in the string?

If there are also no escape characters, then yeah.

FWIW, 8.4 will complain about this case:

regression=# select E'\\' like E'\\';
ERROR: LIKE pattern must not end with escape character

regards, tom lane

Tom Lane wrote:
> Jesper Krogh <jesper(at)krogh(dot)cc> writes:
>> Shouldnt the like operator do the same as the = if there occours no
>> wildcards and stuff in the string?
>
> If there are also no escape characters, then yeah.
>
> FWIW, 8.4 will complain about this case:
>
> regression=# select E'\\' like E'\\';
> ERROR: LIKE pattern must not end with escape character

So I cannot rely on the like operator to behave correct if I'd like to
compare strings with backslashes (e.g. filepaths from MS Windows
filesystems)?

I actually get the same if it doesnt end with the slashes:
testdb=# select E'\\t' like E'\\t';
?column?
----------
f
(1 row)

testdb=# select E'\\t' = E'\\t';
?column?
----------
t
(1 row)

--
Jesper

Jesper Krogh wrote:
> Tom Lane wrote:
>> Jesper Krogh <jesper(at)krogh(dot)cc> writes:
>>> Shouldnt the like operator do the same as the = if there occours no
>>> wildcards and stuff in the string?
>>
>> If there are also no escape characters, then yeah.
>>
>> FWIW, 8.4 will complain about this case:
>>
>> regression=# select E'\\' like E'\\';
>> ERROR: LIKE pattern must not end with escape character
>
> So I cannot rely on the like operator to behave correct if I'd like to
> compare strings with backslashes (e.g. filepaths from MS Windows
> filesystems)?
>
> I actually get the same if it doesnt end with the slashes:
> testdb=# select E'\\t' like E'\\t';
> ?column?
> ----------
> f
> (1 row)
>
> testdb=# select E'\\t' = E'\\t';
> ?column?
> ----------
> t
> (1 row)

Ok. The pattern has to be "double escaped"..

testdb=# select E'\\t' like E'\\\\t';
?column?
----------
t
(1 row)

(for the archives a ref to the documentations i didnt get by the read
through)
http://www.postgresql.org/docs/8.2/static/functions-matching.html#FUNCTIONS-LIKE

--
Jesper

Jesper Krogh <jesper(at)krogh(dot)cc> writes:
> Ok. The pattern has to be "double escaped"..

Or specify a different escape character.

regards, tom lane

Jesper Krogh wrote:

> So I cannot rely on the like operator to behave correct if I'd like to
> compare strings with backslashes (e.g. filepaths from MS Windows
> filesystems)?

test=# SELECT E'\\' LIKE E'\\' ESCAPE '';
?column?
----------
t
(1 row)

--
Craig Ringer