Thread: placeholders

Hi,

I am using
- Postrges 6.3.2
- DBI 0.93
- DBD-pg 0.73
- Slackware 3.3 Linux

I am accessing the database using a perl
CGI program.

I need to be able to list records from a
database in various sort orders. The user
needs to be able to select the sort order
using a web form.

The code I am using which works fine is

$sth1 = $dbh->prepare
   (q
    {
    SELECT DISTINCT
       catalogid,
       productid,
       reference,
       title,
       dateposted,
       dateremove,
       userlastupdate,
       email,
       webaddress,
       phone,
       details,
       category

    FROM product
    WHERE (( catalogid = 'mp')
    AND   ( category like :1 )
    AND   ( details like :2 )
    AND   ( userlastupdate like :3 ))
      ORDER BY title DESC
    }
    );


$counter = 0;
$sth1->execute (("$category\%"),("$keywords\%"), ("$postedby\%"))

or die "$DBI::errstr\n";

while ( (
       $catalogid,
       $productid,
       $reference,
       $title,
       $dateposted,
       $dateremove,
       $userlastupdate,
       $email,
       $webaddress,
       $phone,
       $details,
       $category
        ) = $sth1->fetchrow() )
    {
    $counter = $counter + 1;


After this the CGI writes out HTML
for each row read.

I want to be able to change the code so the
field name in the order by clause is variable

eg. instead of
      ORDER BY title DESC

I want to say
      ORDER BY :4 DESC

and in the execute statement
$sth1->execute (("$category\%"),("$keywords\%"), ("$postedby\%"))

add a fourth variable ("$orderby") which
will be set to title, dateposted or
userlastupdate

However if I use ("$orderby") as the
fourth variable and set $orderby to
title then my trace shows DBI puts
'title' into the SQL SELECT statement
not title and I get an invalid syntax
error. I need to find a way to stop
putting the ' ' around title.

Is there any way I can make the order by
operand a variable ??

Thanks,
Martin Stewart

> Hi,
>
> I am using
> - Postrges 6.3.2
> - DBI 0.93
> - DBD-pg 0.73
> - Slackware 3.3 Linux
>
> I am accessing the database using a perl
> CGI program.
>
> I need to be able to list records from a
> database in various sort orders. The user
> needs to be able to select the sort order
> using a web form.

[...]

>
> I want to be able to change the code so the
> field name in the order by clause is variable
>
> eg. instead of
>       ORDER BY title DESC
>
> I want to say
>       ORDER BY :4 DESC
>
> and in the execute statement
> $sth1->execute (("$category\%"),("$keywords\%"), ("$postedby\%"))
>
> add a fourth variable ("$orderby") which
> will be set to title, dateposted or
> userlastupdate
>
> However if I use ("$orderby") as the
> fourth variable and set $orderby to
> title then my trace shows DBI puts
> 'title' into the SQL SELECT statement
> not title and I get an invalid syntax
> error. I need to find a way to stop
> putting the ' ' around title.
>
> Is there any way I can make the order by
> operand a variable ??
>

    What's wrong with:

    @column = ("catalogid", "productid", ..., "category");

    ... ORDER BY $column[3] DESC ...

If you want it real smart, you can run a query to obtain column names
from the database.

Also, since you are using perl anyway, you might as well delegate
ordering to perl. If you read your entire query output to an array of
strings where values are delimited with something, e. g., "\t", you
could say:

    $colToSortOn = 2;
    $descending = 1; # otherwise $descending = undef;
    foreach ( sort {
            @a = split "\t", $a;
            @b = split "\t", $b;
                ($descending ? $b[$colToSortOn] <=> $a[$colToSortOn] : $a[$colToSortOn] <=> $b[$colToSortOn])
        } @result # @result comes from your query
    ) {
        @values = split "\t";
        # do your display stuff here
    }

See man perlfunc /sort SUBNAME for more details on sort()

At 03:05 7/01/99 , you wrote:
>> Hi,
>>
>> I am using
>> - Postrges 6.3.2
>> - DBI 0.93
>> - DBD-pg 0.73
>> - Slackware 3.3 Linux
>>
>> I am accessing the database using a perl
>> CGI program.
>>
>> I need to be able to list records from a
>> database in various sort orders. The user
>> needs to be able to select the sort order
>> using a web form.
>
>[...]
>
>>
>> I want to be able to change the code so the
>> field name in the order by clause is variable
>>
>> eg. instead of
>>       ORDER BY title DESC
>>
>> I want to say
>>       ORDER BY :4 DESC
>>
>> and in the execute statement
>> $sth1->execute (("$category\%"),("$keywords\%"), ("$postedby\%"))
>>
>> add a fourth variable ("$orderby") which
>> will be set to title, dateposted or
>> userlastupdate
>>
>> However if I use ("$orderby") as the
>> fourth variable and set $orderby to
>> title then my trace shows DBI puts
>> 'title' into the SQL SELECT statement
>> not title and I get an invalid syntax
>> error. I need to find a way to stop
>> putting the ' ' around title.
>>
>> Is there any way I can make the order by
>> operand a variable ??
>>
>
>    What's wrong with:
>
>    @column = ("catalogid", "productid", ..., "category");
>
>    ... ORDER BY $column[3] DESC ...

Gene, Thanks for your reply.

I don't think I can put a perl variable $column[3]
into an sql prepare statement as it gets passed
straight through as $column[3] to DBI and I get
a syntax error from DBI.
ERROR:  parser: parse error at or near "column"

However the sort in Perl looks like the
answer so I will try that next.

Regards, Martin

>
>If you want it real smart, you can run a query to obtain column names
>from the database.
>
>Also, since you are using perl anyway, you might as well delegate
>ordering to perl. If you read your entire query output to an array of
>strings where values are delimited with something, e. g., "\t", you
>could say:
>
>    $colToSortOn = 2;
>    $descending = 1; # otherwise $descending = undef;
>    foreach ( sort {
>            @a = split "\t", $a;
>            @b = split "\t", $b;
>                ($descending ? $b[$colToSortOn] <=> $a[$colToSortOn] : $a[$colToSortOn] <=> $b[$colToSortOn])
>        } @result # @result comes from your query
>    ) {
>        @values = split "\t";
>        # do your display stuff here
>    }
>
>See man perlfunc /sort SUBNAME for more details on sort()
>