Обсуждение: Array or not Array?

On 3 March 2010 10:48, Atif Jung <atifjung@gmail.com> wrote:
> If I have a table as follows:
>
> CREATE TABLE test1 (a char(5));
>
> how would I test that the 2nd character of column a is NOT the letter 'b'
> for example.
>
> In Informix I would say:
>
> SELECT count(*) FROM test1 where a[2] <> 'b';
>
> In POSTGRES I get an error saying "ERROR:  cannot subscript type character
> because it is not an array". I understand why I'm getting the error,  but
> I'm not sure how I do what I want to do?
>

You can use a regular expression like:

SELECT count(*) FROM test1 where a !~ '^.b';

Regards

Thom

In response to Atif Jung :
> If I have a table as follows:
>  
> CREATE TABLE test1 (a char(5));
>  
> how would I test that the 2nd character of column a is NOT the letter 'b' for
> example.
>  
> In Informix I would say:
>  
> SELECT count(*) FROM test1 where a[2] <> 'b';
>  
> In POSTGRES I get an error saying "ERROR:  cannot subscript type character
> because it is not an array". I understand why I'm getting the error,  but I'm
> not sure how I do what I want to do?

You can use the substring() - function:

test=# CREATE TABLE test1 (a char(5));
CREATE TABLE
test=*# copy test1 from stdin;
Enter data to be copied followed by a newline.
End with a backslash and a period on a line by itself.
>> aaa
>> bbb
>> test
>> foo
>> bar
>> \.
test=*# select count(1) from test1 where substring(a,2,1) = 'b';
 count
-------
     1
(1 row)

test=*# select count(1) from test1 where substring(a,2,1) != 'b';
 count
-------
     4
(1 row)



HTH, Andreas
--
Andreas Kretschmer
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