July 6, 2008 09:06pm pdt

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1. ozo 3,574,793
2. Adam314 1,354,703
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5. jmcg 517,810
6. mjcoyne 502,431
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8. maneshr 385,976
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15. Tim_Utschig 113,107

05.03.2008 at 03:41AM PDT, ID: 23373663

	[x] Attachment Details

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9.2

Get next/ back customer in database

Zones: Perl Programming Language, MySQL

Tags: perl mysql

I am using a mysql database using the DBI mod to access it.

The database has some headers:
One of them is the customers number.
1)
What I want to do is to sort on the customer number (cust_id) and then return the data one after the cust_id entered!
2)
What I want to do is to sort on the customer number (cust_id) and then return the data one before the cust_id entered!

So I create a sort of next and back function??

How to do that?

Tables name: sql_table

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Question Stats

Zone: Programming

Question Asked By: mmcw

Solution Provided By: FishMonger

Participating Experts: 2

Solution Grade: A

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05.03.2008 at 09:30AM PDT, ID: 21492846

Rank: Wizard

FishMonger:

Is this what you're looking for?
(note: it doesn't include proper error handling)

                       
         
           
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             my @next_user = get_next($dbh, $cust_id);
my @previous_user = get_previous($dbh, $cust_id);
 
sub get_next {
   my ($dbh, $id) = @_;
   my $sth = $dbh->prepare("select * from sql_table where cust_id = ?");
   $sth->execute($id + 1);
   my @cust_record = $sth->fetchrow_array;
   $sth->finish;
   return @cust_record;
}
 
sub get_previous {
   my ($dbh, $id) = @_;
   my $sth = $dbh->prepare("select * from sql_table where cust_id = ?");
   $sth->execute($id - 1);
   my @cust_record = $sth->fetchrow_array;
   $sth->finish;
   return @cust_record;
}

           
         

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05.03.2008 at 09:34AM PDT, ID: 21492865

mmcw:

But what if the id - 1 not exist anymore because it has been deleted?

05.03.2008 at 09:44AM PDT, ID: 21492903

Rank: Wizard

FishMonger:

Then the array would be undefined, which is easily checked for with a simple conditional test.

if ( @next_user ) {

# do whatever is needed with the customer record

}
else {

# no customer record was found, so do whatever error handling you wish

}

05.03.2008 at 10:51PM PDT, ID: 21494678

mmcw:

This is what I ment:
Is this the right way to do this?
I am new to SQL programming!!

if ($r_in->{'sql_read_back'}) {
      $sth = $dbh->prepare("SELECT * FROM sql_table WHERE cust_id=(SELECT MAX(cust_id) FROM $sql_table WHERE cust_id<'$r_in->{'id'}')");
      $sth->execute();

      $result = $sth->fetchrow_hashref();
}
elsif ($r_in->{'sql_read_forward'}) {
      $sth = $dbh->prepare("SELECT * FROM $sql_table WHERE cust_id=(SELECT MIN(cust_id) FROM $sql_table WHERE cust_id>'$r_in->{'id'}')");
      $sth->execute();

      $result = $sth->fetchrow_hashref();
}

05.04.2008 at 10:31PM PDT, ID: 21498270

Rank: Genius

Adam314:

If you wanted, you could get all of the customer records, sorted by ID. You could then search through that to find the "entered" id, and then look at the previous and next records (if any). This could be much slower than just requesting the records you actually want though (which is what FishMonger's script does - it just gets the two records).

From your code, I'm not sure what you are trying to do.
What are $r_in->{sql_read_back} and $r_in->{sql_read_forward}? Are these where the user would select either "previous" or "next" record from the selected $r_in->{id}?

05.05.2008 at 12:16PM PDT, ID: 21502264

mmcw:

The problem is that for example after the id 1 the id 15 comes.
And there are more filters that wil cause more id holes in the id range!!!!
Thats why I thought I use the code I given in my last comment!!
Is there a better way!

From your code, I'm not sure what you are trying to do.
What are $r_in->{sql_read_back} and $r_in->{sql_read_forward}? Are these where the user would select either "previous" or "next" record from the selected $r_in->{id}?
YES THAT IS!!

05.05.2008 at 12:56PM PDT, ID: 21502527

Rank: Genius

Adam314:

Then, yes, what you have would work. It might need a few minor changes. Is the table named sql_table, or is $sql_table a variable that contains the name of the table? If it is the name of the table, you don't need a $ in front of sql_table (you have 3 places with a $). If it is a variable, you will need the $ (you have 1 place without $).

I'm not to familar with SQL (only know the basics) - so I don't know if what you have is valid. If so, then:
The cust_id is numeric, correct? If so, you don't need to put it in quotes:
$sth = $dbh->prepare("SELECT * FROM sql_table WHERE cust_id=(SELECT MAX(cust_id) FROM $sql_table WHERE cust_id<$r_in->{id})");

If not, you might need two sql statements - one to get the cust_id of the prev/next record, then one to get that record.

05.05.2008 at 01:49PM PDT, ID: 21502885

Rank: Wizard

FishMonger:

Using a select within a select statement isn't the most efficient approach. It would be better to use the ORDER BY and LIMIT clauses. I would also factor out the redundant portions of the if/else block.

This is untested, but I think I got the order by clause in the correct order. If not, just swap ASC and DESC.

                       
         
           
           
             my $sth;
if ($r_in->{'sql_read_back'}) {
      $sth = $dbh->prepare("SELECT *
                            FROM  sql_table
                            WHERE cust_id < $r_in->{'id'}
                            ORDER BY cust_id DESC
                            LIMIT 1");
}
elsif ($r_in->{'sql_read_forward'}) {
      $sth = $dbh->prepare("SELECT *
                            FROM $sql_table
                            WHERE cust_id >$r_in->{'id'}
                            ORDER BY cust_id ASC
                            LIMIT 1");
}
$sth->execute();
my $result = $sth->fetchrow_hashref();

           
         

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Accepted Solution

20080236-EE-VQP-29 / EE_QW_2_20070628