2018. 05. 07. 12:26 keltezéssel, Dimitry Sibiryakov sd@...
[firebird-support] írta:

> 07.05.2018 12:19, Gabor Boros mlnglsts@... [firebird-support] wrote:
>> A simple example: SELECT ''='' SIMILAR TO '[A-Z]{2}[0-9A-Z]{2,13}' FROM
>> RDB$DATABASE
>>
>> Why is the result true?
>
> Your expression is actually calculated as "CAST(''='' as CHAR(5)) SIMILAR TO
> '[A-Z]{2}[0-9A-Z]{2,13}'".
> (''='') is true and string representation of true is 'TRUE ' that matches your patters.

Result of

SELECT '*' || CAST(''='' AS CHAR(5)) || '*',
CHARACTER_LENGTH(CAST(''='' AS CHAR(5))) FROM RDB$DATABASE

is

CONCATENATION CHAR_LENGTH
============= ============
*TRUE * 5

So I see what you say. But result of

SELECT CAST(''='' AS CHAR(5)) SIMILAR TO '[A-Z]{2}[0-9A-Z]{2,13}' FROM
RDB$DATABASE;

is

=======
<false>

So put the two case into one query

SELECT ''='' SIMILAR TO '[A-Z]{2}[0-9A-Z]{2,13}', CAST(''='' AS
CHAR(5)) SIMILAR TO '[A-Z]{2}[0-9A-Z]{2,13}' FROM RDB$DATABASE;

and the result is

======= =======
<true> <false>

And result of

SELECT 'TRUE ' SIMILAR TO '[A-Z]{2}[0-9A-Z]{2,13}' FROM RDB$DATABASE

is

=======
<false>

Gabor