This is probably a somewhat simple question but I am trying to make sure that a query statement (specifically a select statement) contains a specific number of parameters only:
$result = mysql_query("select type,some_other_column from my_table");
$row = mysql_fetch_array($result);
$number = count($row);
print $number;
This returns twice the number I think it should return (4) - as I believe it must also be returning the key and the value as separate parameters.
The select statement above is just an example and it could be any number of statements. They could be a lot more complicated and the tests I have run do not seem to have any problems. I want to make sure that there are only ever two parameters (it can be any two) and they could be from different tables too.
I just want to make sure that it that what I am doing above is both the fastest way to check that the number of parameters is correct and that it won't get upset if there is a much more complicated statement given to it.
I am sure there is a really easy answer to this. Thanks in advance for any help.
Try mysql_fetch_assoc or mysql_fetch_row. Both functions available on php.net
mysql_fetch_array -- Fetch a result row as an associative array, a numeric array, or both. You end up having
$row["type"] = "somevalue"; // AND
$row[0] = "somevalue";
hence double the number
Whatever you SELECT would be in the $row variable, so in your code:
$result = mysql_query("select type,some_other_column from my_table");
$row = mysql_fetch_array($result);
/*
$row = array(
'type' => 'type_value',
'0' => 'type_value',
'some_other_column' => 'col_value',
'1' => 'col_value'
)
*/
$number = count($row);
print $number; // prints 4
I am not sure i understood your question right.
Do you just want to limit your number of returned values to one row?
If this is your point, you can add LIMIT 1 to your SQL-Query. This would, as it says, limit the number of results to one row.
Related
I have this code to get a value count.
Short way:
my $count = $dbh->selectrow_array("SELECT COUNT(name) AS RESCOUNT FROM users");
Long way
my $sth = $dbh->prepare("SELECT COUNT(name) AS RESCOUNT FROM users");
$sth->execute() or die "$DBI::errstr";
my $count = $sth->fetchrow_array();
$sth->finish;
selectrow_array, fetchrow_array --> but I don't need an array. I checked the docs, but found nothing for scalars. Just methods for arrays and hashes.
The method I use is fast enough, but I was just curious if there is a better, fastest way to get a single value from the call. Or this is the fastest possible way?
The fastest way is to use fetchrow_arrayref or selectrow_arrayref, depending on how many executes you have. This only really makes a difference if executed in a loop and you have thousands (or rather hundreds of thousands) of rows.
When using fetchrow_array, it will make a copy every time, which slows you down. Also keep in mind that the behaviour for scalar context is only partly defined.
If called in a scalar context for a statement handle that has more than one column, it is undefined whether the driver will return the value of the first column or the last. So don't do that.
You can also do bind_col, which works with references.
There used to be a good presentation on DBI speeds from about 10 or more years ago that I can't find right now. Also take a look at this very old Perlmonks post, that explains quite a bit about performance.
Keep in mind that you should only do optimisation when you really know you need it. Most of the time you won't.
If "modern" means "I only heard of it recently", I'm feeling all modern with DBI's bind_col and bind_columns. Cribbing from a post by DBI hero Tim Bunce...
For your case:
my $sth = $dbh->prepare("SELECT COUNT(name) AS RESCOUNT FROM users");
my $count = 0;
$sth->bind_col(1,\$count); # bind to a reference to the variable
$sth->execute() or die "$DBI::errstr";
$sth->fetch;
print $count;
In a loop for a SELECT statement returning multiple records:
my $sth = $dbh->prepare(qq{SELECT name FROM users WHERE zip_code == '20500'});
my $name = '';
$sth->bind_col(1,\$name); # bind to a reference to the variable
$sth->execute() or die "$DBI::errstr";
while ($sth->fetch) {
print $name, "\n";
}
And with bind_columns this works:
my $sth = $dbh->prepare(qq{SELECT name,phone,address FROM users WHERE zip_code == '20500'});
my #fields = qw/name phone address/;
# With a 'SELECT All * ...', get all columns with #{$sth->{NAME_lc}}
my %data;
$sth->bind_columns( \( #data{#fields} ) ); # \(...) gives references to its elements
$sth->execute() or die "$DBI::errstr";
while ($sth->fetch) {
print "$data{name} lives at $data{address}, with phone $data{phone}.", "\n";
}
Once the setup is handled, the looping is simple to write and fast to run. (But, benchmark).
HTH, apologize if this diverges too much from the OP's problem statement. But it's the simplest and most direct way to get your returned data into the form of variable(s) you want, so you can move on to doing something with it...
I can do this all as one function, but in trying to port it over to my packages of functions (library) I am missing something.
Here's what I want to do from my main Perl script
my #rows;
$result = Funx::dbcdata($myConnection,
"SELECT * FROM Inv where name like \"%DOG%\";", \#rows);
Then in my library package I am attempting this
sub dbcdata
{
my ($connection, $command, $array) = #_;
my $query = $connection->prepare($command);
my $result = $query->execute();
my $i =0;
while(my $row = $query->fetchrow_arrayref() )
{
#{$array}[$i] = $row;
$i++;
}
$query->finish;
return $result;
}
I was hoping to get back pointers or references to each row (which was 4in this case) but am not. Every element in #rows is the same:
ARRAY(0x5577a0f77ec0) ARRAY(0x5577a0f77ec0) ARRAY(0x5577a0f77ec0)
ARRAY(0x5577a0f77ec0)
Nor do I know how to turn each one into the original separate row. Any help would be appreciated, thanks.
From the documentation for fetchrow_arrayref:
Note that the same array reference is returned for each fetch, so don't store the reference and then use it after a later fetch. Also, the elements of the array are also reused for each row, so take care if you want to take a reference to an element.
Sounds like you want fetchall_arrayref:
The fetchall_arrayref method can be used to fetch all the data to be returned from a prepared and executed statement handle. It returns a reference to an array that contains one reference per row.
After executing the statement, you can do something like
#{$array} = $query->fetchall_arrayref->#*;
instead of that ugly loop.
But selectall_array might be even better. Your whole function can be replaced by a call to it:
my #rows =
$myConnection->selectall_array(q/SELECT * FROM Inv WHERE name LIKE '%DOG%'/);
I am not able to retrieve the output properly using the below code. Please help me to sort it out.
I am getting output differently to run in MySQL and Perl.
As of now it is returning undef when I use Dumper. But I want it to display null.
$reactivate_sth = $dbh->prepare("
SELECT
a,
b
FROM
table
WHERE
c = ?
AND
d = ?
ORDER BY
date DESC
");
$reactivate_sth->execute($c, $d);
print $result = $reactivate_sth->fetchrow_hashref();
OUTPUT:
MySQL:
Empty set (0.00 sec)
Perl:
HASH(0x3068198)
Data::Dumper
VAR1 = undef
You must make your code more readable. It's often useful to use a heredoc to quote SQL statements, like this
my $reactivate_sth = $dbh->prepare(<<END_SQL);
SELECT a, b
FROM table
WHERE c = ? AND d = ?
ORDER BY date DESC
END_SQL
$reactivate_sth->execute($c, $d);
my $result = $reactivate_sth->fetchrow_hashref;
Now $result is a reference to a hash, because you called the fetchrow_hashref method. Printing it will, as you have found, produce something like HASH(0x1cc5a8). You need to access the elements of the hash to make sense of the result
After that, I don't know what output you want. You can use the core Data::Dumper module to display the record that you've retrieved like this
use Data::Dumper;
print Dumper $result;
Does that help? You haven't asked for anything more
Finally I found the solution for this issue. I am not sure this one is a proper fix or not.
Please guide me if the fix is not professional.
if (!defined $result->{''}) {
$result = '';
}
I've been out of the mysql and perl game for quite a few years and can't seem to get this right. I have a table with just 3 columns. 'cnt' is one of them. All I want to do is query the table on 'name' and see if name exists. If it does, I want to capture the value of 'cnt'. The table has a record of testName with a value of 2 I added manually. When this script is run it returns empty.
my $count;
my $pop = qq(SELECT cnt FROM popular WHERE name="testName");
my $sth = $dbh->prepare($pop);
$sth->execute() or die $dbh->errstr;
my #return;
while (#return = $sth->fetchrow_array()) {
$count = $return[1];
}
print "our return count is $count";
Is it obvious to anyone what I did wrong?
You probably mean
$count = $return[0];
According to perl doc on mysql
An alternative to fetchrow_arrayref. Fetches the next row of data and returns it as a list containing the field values.
Since you select cnt as the return value ,so , the size of #return is 1,but you misunderstand it as the number of results which meets your query condition.No, it is not so!Please have a more careful reading of perl doc.
I expect this is a simple coding error.
When trying to get all results from database table, the first result is always missed off. Even when adding and removing information to the database it will always miss off the result with the lowest ID.
$data = mysql_query("SELECT * FROM tbl_messages")
or die(mysql_error());
$info = mysql_fetch_array( $data );
while($info = mysql_fetch_array( $data ))
{
Print "" .$info['subject']. "";
echo "<hr>";
}
Your current code calls mysql_fetch_array and assigns the result (the first row of the result set) to $info. You don't do anything with $info, and in the next line you overwrite it with another call to mysql_fetch_array.
You need to delete this line:
$info = mysql_fetch_array( $data );
From the php manual:
array mysql_fetch_array ( resource $result [, int $result_type = MYSQL_BOTH ] )
Returns an array that corresponds to the fetched row and moves the internal data pointer ahead.
So after
$data = mysql_query(...) you get an array $data and the internal data pointer points on the first element of $data.
The first call of mysql_fetch_array(...) moves the internal data point ahead, so it now points to the second element.
Then, your while-loop calls mysql_fetch_array(...) AGAIN before issuing the first Print, so the second element gets printed.
You can fix it by removing this line:
$info = mysql_fetch_array( $data );
Remove the first mysql_fetch_array statement.
something like
$data = mysql_query("SELECT * FROM tbl_messages")
or die(mysql_error());
while($info = mysql_fetch_array( $data ))
{
Print "" .$info['subject']. "";
echo "<hr>";
}
You are skipping the first entry by using the code as above.
From mysql_fetch_array
Returns an array that corresponds to the fetched row and moves the
internal data pointer ahead.
Which means that when you get to the while, you have already read the first row, but not used it yet.
I had problems like this too with my table query's ignoring row 0 (the first occurance) and now that I see this I finally understand what's going on.
The clarification is also understandable.
You are asking for a query_fetch_array and you put what it finds in $info. This seems ok. Next you ask for the remaining rows, since you just removed one row from the possible returns, it also works perfectly.
Remove this line:
$info = mysql_fetch_array( $data );
and you get all your rows from your table. Or, if you are wondering, ECHO the $info before your while loop in the fashion you are printing or just try var_dumping it.