Enumerating over several cells in MySQL DB using PHP - php

Problem: I have several rows of results, for a single survey. Each survey can have any number of rows in the "Results" Table. There's a column called key_value. It's either 0 or -1. What is the fastest way in PHP to enumerate over several rows in a MySQL database, access each object, and flag a Boolean in PHP to tell me whether or not this particular survey has any rows with a key_value of 0?
something like this, except not brute forcing it...
for (i = 0; i < mysqlrows.length; i++){
if (mysqlrow.key_value == 0)
flag = true;
else
flag = false;
}

To operate on all matching (key_value = 0) Results:
$query = <<<EOD
SELECT result_id
FROM Results
WHERE key_value = 0
EOD;
$pdo = new PDO(....);
$stmt = $pdo->prepare($query);
if ($stmt->execute()) {
while ($result = $stmt->fetch(PDO::FETCH_ASSOC)) {
$result_id = $result['result_id'];
//do something with this result?
}
}
But if you only wanted the number of Results with key_value = 0, use some SQL like:
SELECT COUNT(*) as num_with_zero FROM Results WHERE key_value = 0

Related

How to count a column in database and if empty return 0 PHP

I have a table where I want to count total entries in one column. But if the entire column is empty, I want the count to return 0 (meaning there are zero entries)
This is what I tried, but when I use echo it returns blank. In the database it is blank, but I want it to return 0 when column recall is empty.
CODE:
$chartsql = "SELECT recall from report where child_id='$childId'";
$ChartRes = mysqli_query($con,$chartsql);
while ($ChartRow=mysqli_fetch_array($ChartRes)){
$recall[] = $ChartRow['recall1'];
}
foreach($recall as $index=>$value) {
if($value === null) unset($recall[$index]);
}
$count_recall = count($recall);
if($count_recall = ''){
$count_recall1 = 0;
}
echo $count_recall;
Also, in the recall column, there are null entries as well as blank entries. So I want to ignore the nulls, but if all other entries are blank then it should return zero. If there are some blank and some valid entries, then it should only count the valid entries and not what is blank.
It should only return 0 if it is completely empty, ignoring nulls.
Use SQL count function instead:
$chartsql = "SELECT count(child_id) as totalitems from report where child_id='$childId' and recall is not null and recall != ''";
$ChartRes = mysqli_query($con,$chartsql);
$ChartRow = mysqli_fetch_array($ChartRes);
$count_recall = $ChartRow['totalitems'];
Never use PHP for counting, when you can use SQL for your result, because:
When you have many rows, you will have performance issue.
You can easily do it inside your query and have cleaner codes.
Debugging is much easier.
How about count(*)
https://dev.mysql.com/doc/refman/8.0/en/counting-rows.html
$chartsql = "SELECT count(*) from report where child_id='$childId'" and recall is not null and recall != ''";
<?php
$chartsql =
"SELECT (count(id) - (
SELECT count(id)
FROM report
WHERE attributeName LIKE ''))
FROM report";
?>
All you need to do is substract the total of rows to the amout of empty rows. It should do the job
In PHP you could simplify it by:
assign only valid value to $recall array
add zero to returned value from count() to make it an integer
<?php
$chartsql = "SELECT recall from report where child_id='$childId'";
$ChartRes = mysqli_query($con,$chartsql);
while ($ChartRow=mysqli_fetch_array($ChartRes)){
if(!is_null($ChartRow['recall1'])){
$recall[] = $ChartRow['recall1'];
}
}
$count_recall = count($recall) + 0;
echo $count_recall;

count total rows in MySQL and number of rows based on a where statement [duplicate]

There are many conflicting statements around. What is the best way to get the row count using PDO in PHP? Before using PDO, I just simply used mysql_num_rows.
fetchAll is something I won't want because I may sometimes be dealing with large datasets, so not good for my use.
Do you have any suggestions?
$sql = "SELECT count(*) FROM `table` WHERE foo = ?";
$result = $con->prepare($sql);
$result->execute([$bar]);
$number_of_rows = $result->fetchColumn();
Not the most elegant way to do it, plus it involves an extra query.
PDO has PDOStatement::rowCount(), which apparently does not work in MySql. What a pain.
From the PDO Doc:
For most databases,
PDOStatement::rowCount() does not
return the number of rows affected by
a SELECT statement. Instead, use
PDO::query() to issue a SELECT
COUNT(*) statement with the same
predicates as your intended SELECT
statement, then use
PDOStatement::fetchColumn() to
retrieve the number of rows that will
be returned. Your application can then
perform the correct action.
EDIT: The above code example uses a prepared statement, which is in many cases is probably unnecessary for the purpose of counting rows, so:
$nRows = $pdo->query('select count(*) from blah')->fetchColumn();
echo $nRows;
As I wrote previously in an answer to a similar question, the only reason mysql_num_rows() worked is because it was internally fetching all the rows to give you that information, even if it didn't seem like it to you.
So in PDO, your options are:
Use PDO's fetchAll() function to fetch all the rows into an array, then use count() on it.
Do an extra query to SELECT COUNT(*), as karim79 suggested.
Use MySQL's FOUND_ROWS() function UNLESS the query had SQL_CALC_FOUND_ROWS or a LIMIT clause (in which case the number of rows that were returned by the query and the number returned by FOUND_ROWS() may differ). However, this function is deprecated and will be removed in the future.
As it often happens, this question is confusing as hell. People are coming here having two different tasks in mind:
They need to know how many rows in the table
They need to know whether a query returned any rows
That's two absolutely different tasks that have nothing in common and cannot be solved by the same function. Ironically, for neither of them the actual PDOStatement::rowCount() function has to be used.
Let's see why
Counting rows in the table
Before using PDO I just simply used mysql_num_rows().
Means you already did it wrong. Using mysql_num_rows() or rowCount() to count the number of rows in the table is a real disaster in terms of consuming the server resources. A database has to read all the rows from the disk, consume the memory on the database server, then send all this heap of data to PHP, consuming PHP process' memory as well, burdening your server with absolute no reason.
Besides, selecting rows only to count them simply makes no sense. A count(*) query has to be run instead. The database will count the records out of the index, without reading the actual rows and then only one row returned.
For this purpose the code suggested in the accepted answer is fair, save for the fact it won't be an "extra" query but the only query to run.
Counting the number rows returned.
The second use case is not as disastrous as rather pointless: in case you need to know whether your query returned any data, you always have the data itself!
Say, if you are selecting only one row. All right, you can use the fetched row as a flag:
$stmt->execute();
$row = $stmt->fetch();
if (!$row) { // here! as simple as that
echo 'No data found';
}
In case you need to get many rows, then you can use fetchAll().
fetchAll() is something I won't want as I may sometimes be dealing with large datasets
Yes of course, for the first use case it would be twice as bad. But as we learned already, just don't select the rows only to count them, neither with rowCount() nor fetchAll().
But in case you are going to actually use the rows selected, there is nothing wrong in using fetchAll(). Remember that in a web application you should never select a huge amount of rows. Only rows that will be actually used on a web page should be selected, hence you've got to use LIMIT, WHERE or a similar clause in your SQL. And for such a moderate amount of data it's all right to use fetchAll(). And again, just use this function's result in the condition:
$stmt->execute();
$data = $stmt->fetchAll();
if (!$data) { // again, no rowCount() is needed!
echo 'No data found';
}
And of course it will be absolute madness to run an extra query only to tell whether your other query returned any rows, as it suggested in the two top answers.
Counting the number of rows in a large resultset
In such a rare case when you need to select a real huge amount of rows (in a console application for example), you have to use an unbuffered query, in order to reduce the amount of memory used. But this is the actual case when rowCount() won't be available, thus there is no use for this function as well.
Hence, that's the only use case when you may possibly need to run an extra query, in case you'd need to know a close estimate for the number of rows selected.
I ended up using this:
$result = $db->query($query)->fetchAll();
if (count($result) > 0) {
foreach ($result as $row) {
echo $row['blah'] . '<br />';
}
} else {
echo "<p>Nothing matched your query.</p>";
}
This post is old but Getting row count in php with PDO is simple
$stmt = $db->query('SELECT * FROM table');
$row_count = $stmt->rowCount();
This is super late, but I ran into the problem and I do this:
function countAll($table){
$dbh = dbConnect();
$sql = "select * from `$table`";
$stmt = $dbh->prepare($sql);
try { $stmt->execute();}
catch(PDOException $e){echo $e->getMessage();}
return $stmt->rowCount();
It's really simple, and easy. :)
This is an old post, but getting frustrated looking for alternatives. It is super unfortunate that PDO lacks this feature, especially as PHP and MySQL tend to go hand in hand.
There is an unfortunate flaw in using fetchColumn() as you can no longer use that result set (effectively) as the fetchColumn() moves the needle to the next row. So for example, if you have a result similar to
Fruit->Banana
Fruit->Apple
Fruit->Orange
If you use fetchColumn() you can find out that there are 3 fruits returned, but if you now loop through the result, you only have two columns, The price of fetchColumn() is the loss of the first column of results just to find out how many rows were returned. That leads to sloppy coding, and totally error ridden results if implemented.
So now, using fetchColumn() you have to implement and entirely new call and MySQL query just to get a fresh working result set. (which hopefully hasn't changed since your last query), I know, unlikely, but it can happen. Also, the overhead of dual queries on all row count validation. Which for this example is small, but parsing 2 million rows on a joined query, not a pleasant price to pay.
I love PHP and support everyone involved in its development as well as the community at large using PHP on a daily basis, but really hope this is addressed in future releases. This is 'really' my only complaint with PHP PDO, which otherwise is a great class.
Answering this because I trapped myself with it by now knowing this and maybe it will be useful.
Keep in mind that you cant fetch results twice. You have to save fetch result into array, get row count by count($array), and output results with foreach.
For example:
$query = "your_query_here";
$STH = $DBH->prepare($query);
$STH->execute();
$rows = $STH->fetchAll();
//all your results is in $rows array
$STH->setFetchMode(PDO::FETCH_ASSOC);
if (count($rows) > 0) {
foreach ($rows as $row) {
//output your rows
}
}
If you just want to get a count of rows (not the data) ie. using COUNT(*) in a prepared statement then all you need to do is retrieve the result and read the value:
$sql = "SELECT count(*) FROM `table` WHERE foo = bar";
$statement = $con->prepare($sql);
$statement->execute();
$count = $statement->fetch(PDO::FETCH_NUM); // Return array indexed by column number
return reset($count); // Resets array cursor and returns first value (the count)
Actually retrieving all the rows (data) to perform a simple count is a waste of resources. If the result set is large your server may choke on it.
Have a look at this link:
http://php.net/manual/en/pdostatement.rowcount.php
It is not recommended to use rowCount() in SELECT statements!
When it is matter of mysql how to count or get how many rows in a table with PHP PDO I use this
// count total number of rows
$query = "SELECT COUNT(*) as total_rows FROM sometable";
$stmt = $con->prepare($query);
// execute query
$stmt->execute();
// get total rows
$row = $stmt->fetch(PDO::FETCH_ASSOC);
$total_rows = $row['total_rows'];
credits goes to Mike # codeofaninja.com
To use variables within a query you have to use bindValue() or bindParam(). And do not concatenate the variables with " . $variable . "
$statement = "SELECT count(account_id) FROM account
WHERE email = ? AND is_email_confirmed;";
$preparedStatement = $this->postgreSqlHandler->prepare($statement);
$preparedStatement->bindValue(1, $account->getEmail());
$preparedStatement->execute();
$numberRows= $preparedStatement->fetchColumn();
GL
A quick one liner to get the first entry returned. This is nice for very basic queries.
<?php
$count = current($db->query("select count(*) from table")->fetch());
?>
Reference
I tried $count = $stmt->rowCount(); with Oracle 11.2 and it did not work.
I decided to used a for loop as show below.
$count = "";
$stmt = $conn->prepare($sql);
$stmt->execute();
echo "<table border='1'>\n";
while($row = $stmt->fetch(PDO::FETCH_OBJ)) {
$count++;
echo "<tr>\n";
foreach ($row as $item) {
echo "<td class='td2'>".($item !== null ? htmlentities($item, ENT_QUOTES):" ")."</td>\n";
} //foreach ends
}// while ends
echo "</table>\n";
//echo " no of rows : ". oci_num_rows($stmt);
//equivalent in pdo::prepare statement
echo "no.of rows :".$count;
For straight queries where I want a specific row, and want to know if it was found, I use something like:
function fetchSpecificRow(&$myRecord) {
$myRecord = array();
$myQuery = "some sql...";
$stmt = $this->prepare($myQuery);
$stmt->execute(array($parm1, $parm2, ...));
if ($myRecord = $stmt->fetch(PDO::FETCH_ASSOC)) return 0;
return $myErrNum;
}
The simplest way, it is only 2 lines,
$sql = $db->query("SELECT COUNT(*) FROM tablename WHERE statement='condition'");
echo $sql->fetchColumn();
So, the other answers have established that rowCount() shouldn't be used to count the rows of a SELECT statement. The documentation even says, that :
PDOStatement::rowCount() returns the number of rows affected by the last DELETE, INSERT, or UPDATE statement executed by the corresponding PDOStatement object.
https://web.archive.org/web/20220409162106/https://www.php.net/manual/en/pdostatement.rowcount.php
So it's okay for other queries, but not great for SELECT. Most answers suggest that you should make two queries, one to count rows, and one to get the subset of records you need. However, you could query the row count and your subset of the data in one request. This is a bit of an exercise in code golf, but could actually prove more efficient than two requests if the request time is a bit costly and these requests are made frequently.
If you're in PostgreSQL you can provide clean JSON output, like so:
WITH mytable as (VALUES(1,2,3),(4,5,6),(7,8,9),(10,11,12))
SELECT
jsonb_build_object(
'rowcount', (SELECT count(1) FROM mytable)
,'data', (
SELECT jsonb_agg(data.*)
FROM (
SELECT *
FROM mytable
WHERE column1 > 1 -- pagination offset
ORDER BY column1
LIMIT 2 -- page size
) as data
)
) jsondata
Output:
{"data": [
{
"column1": 4,
"column2": 5,
"column3": 6
},
{
"column1": 7,
"column2": 8,
"column3": 9
}
],
"rowcount": 4
}
If you're not in postgres, those functions won't be available, but you could do this:
WITH mytable as (VALUES(1,2,3),(4,5,6),(7,8,9),(10,11,12))
SELECT
(SELECT count(1) FROM mytable) as rowcount
,data.*
FROM (
SELECT *
FROM mytable as mytable(column1, column2, column3)
WHERE column1 > 1 -- pagination offset
ORDER BY column1
LIMIT 2 -- page size
) as data
but it will return the rowcount on every row, which might be a bit wasteful:
rowcount
column1
column2
column3
4
4
5
6
4
7
8
9
when you make a COUNT(*) in your mysql statement like in
$q = $db->query("SELECT COUNT(*) FROM ...");
your mysql query is already counting the number of result why counting again in php? to get the result of your mysql
$q = $db->query("SELECT COUNT(*) as counted FROM ...");
$nb = $q->fetch(PDO::FETCH_OBJ);
$nb = $nb->counted;
and $nb will contain the integer you have counted with your mysql statement
a bit long to write but fast to execute
Edit:
sorry for the wrong post but as some example show query with count in, I was suggesting using the mysql result, but if you don't use the count in sql fetchAll() is efficient, if you save the result in a variable you won't loose a line.
$data = $dbh->query("SELECT * FROM ...");
$table = $data->fetchAll(PDO::FETCH_OBJ);
count($table) will return the number of row and you can still use the result after like $row = $table[0] or using a foreach
foreach($table as $row){
print $row->id;
}
Here's a custom-made extension of the PDO class, with a helper function to retrieve the number of rows included by the last query's "WHERE" criteria.
You may need to add more 'handlers', though, depending on what commands you use. Right now it only works for queries that use "FROM " or "UPDATE ".
class PDO_V extends PDO
{
private $lastQuery = null;
public function query($query)
{
$this->lastQuery = $query;
return parent::query($query);
}
public function getLastQueryRowCount()
{
$lastQuery = $this->lastQuery;
$commandBeforeTableName = null;
if (strpos($lastQuery, 'FROM') !== false)
$commandBeforeTableName = 'FROM';
if (strpos($lastQuery, 'UPDATE') !== false)
$commandBeforeTableName = 'UPDATE';
$after = substr($lastQuery, strpos($lastQuery, $commandBeforeTableName) + (strlen($commandBeforeTableName) + 1));
$table = substr($after, 0, strpos($after, ' '));
$wherePart = substr($lastQuery, strpos($lastQuery, 'WHERE'));
$result = parent::query("SELECT COUNT(*) FROM $table " . $wherePart);
if ($result == null)
return 0;
return $result->fetchColumn();
}
}
You can combine the best method into one line or function, and have the new query auto-generated for you:
function getRowCount($q){
global $db;
return $db->query(preg_replace('/SELECT [A-Za-z,]+ FROM /i','SELECT count(*) FROM ',$q))->fetchColumn();
}
$numRows = getRowCount($query);
There is a simple solution. If you use PDO connect to your DB like this:
try {
$handler = new PDO('mysql:host=localhost;dbname=name_of_your_db', 'your_login', 'your_password');
$handler -> setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch (PDOException $e) {
echo $e->getMessage();
}
Now, if you want to know how many rows are existing in your table and you have for example column 'id' as the primary key, the query to DB will be:
$query = $handler->query("SELECT id FROM your_table_name");
And finally, to get the amount of the rows matching your query, write like this:
$amountOfRows = $query->rowCount();
Or you can write:
$query = $handler ->query("SELECT COUNT(id) FROM your_table_name");
$amountOfRows = $query->rowCount();
Or, if you want to know how many products there are in the table 'products' have the price between 10 and 20, write this query:
$query = $handler ->query("SELECT id FROM products WHERE price BETWEEN 10 AND
20");
$amountOfRows = $query->rowCount();

SQLite query not returning all result rows

I am trying to pull out a section of rows from a SQLite 3 database using the following code:
function getunsolved($user) {
$sql = "SELECT challenge FROM completed WHERE status = 0 AND username = '$user';";
$rez = $this->query($sql);
$temp = $rez->fetchArray(SQLITE3_NUM);
return $temp;
}
Unfortunately, the code is only returning 1 row, and should be returning 9 rows.
Running the above SQL code on the database, and substituting a valid username for $user returns the correct amount of rows, so I know the problem isn't the SQL code.
My table format is as follows:
username (TEXT), challenges (TEXT), status (INTEGER) (in that order, if it matters)
According to the manual:
SQLite3Result::fetchArray - Fetches a result row as an associative or numerically indexed array or both. By default, fetches as both.
So if you want to get all of the results, you should iterate over them and return the aggregated data:
$ret = array();
while($row = $rez->fetchArray(SQLITE3_NUM)) {
$ret[] = $row;
}
return $ret;

MySQL query in a PHP while loop returns NULL after first result

I have some mysql tables (one for each container) like so (the table would be called containerA for instance):
Box_ID Box_Name Box_Distributor Container Box_state
======---========---===============---==========----=========
1 Box 1 Delivery Comp.1 ContainerA Full
2 Box 2 Delivery Comp.2 ContainerA Empty
3 Box 3 NULL ContainerA Missing
and I have another mysql table with a list of containers:
container_id container_name
============---==============
1 A
2 B
and I want to report the name of the container and the number of empty boxes to a webpage.
I've written this to do it:
$v1 = 0;
$sql = "select * from containers";
$result = mysql_query ($sql) or die(mysql_error());
while ($row = mysql_fetch_array($result))
{
$containers[] = $row[container_name];
$containerid[] = $row[container_id];
}
while ($v1 < 14)
{
$containerend = $containers[$v1];
$containerstart = "container";
$containername = $containerstart.$containerend;
$sql = "SELECT COUNT(*) FROM `$containername` WHERE state = 'Empty';";
$result = mysql_query($sql) or die(mysql_error());
$count = mysql_fetch_array($result);
var_dump($containers[$v1]);
var_dump($count[$v1]);
$v2 = $v1 + 1;
$v1 = $v2;
}
Which works in listing the container names, but it only gives me the first result for the empty boxes, the rest of the array is returned as NULL:
string(1) "4" NULL NULL NULL NULL NULL NULL NULL NULL NULL NULL NULL NULL NULL
Am I doing something stupid here? Surely the SQL query in the while loop should be returning the count for each container?
Any help is appreciated.
change this
while ($row = mysql_fetch_array($result))
{
$containers[] = $row[container_name];
$containerid[] = $row[container_id];
}
to
while ($row = mysql_fetch_array($result))
{
$containers[] = $row['container_name'];
$containerid[] = $row['container_id'];
}
you missed '.
Am I doing something stupid here?
Yes.
Splitting the same data across multiple tables is really dumb.
$sql = "select * from containers";
...
while ($v1 < 14)
{
...
$sql = "SELECT COUNT(*) FROM `$containername` WHERE state = 'Empty';";
Relational database management systems are very good at performing joins. Procedural / OO languages are NOT.
If all your containerX tables where in a single table then the performance would be a lot better and the code much simpler. And it's trivial to create views named like the individual tables on an aggregated table thus avoiding having to rewrite most of your code straight away.
Why are you fetching all the containers then only processing the first 14?
What is $v2 doing?
It's rather hard to work out why your code is misbehaving as your description doesn't match your code - your query states "WHERE state = 'Empty'" but your table description has no column named state (and if that were an accurate report, then the code would stop on the first iteration with a MySQL error message).
$count is in essence only a single value (as you are counting a single container), so it will work for the first element, but not for subsequent elements. Quick fix is to use mysql_result:
$count = mysql_result($result, 0);
as ever, this code is using mysql functions that are both insecure and due to be deprecated - do consider switching to mysqli or pdo.

Testing a SQL Query for True or False

$sql = "SELECT # FROM users WHERE onduty = 1 AND loc_id = '{$site}';";
$result = mysql_query($sql);
I simply want to test if this is true or false. If it returns 0 rows, I want next line to be something like:
if (!$result) { //do this; }
However, in my test, I am getting false when I know it should be true. Is this sound logic here?
(note, yes I know I should be using mysqli_query, that is not what I am asking here)**
ANSWER:
This is what I used:
$login_state = false;
if(mysql_num_rows(mysql_query("SELECT 1 FROM users WHERE onduty = 1 AND loc_id = '{$site}';"))) {
$login_state = true;
}
Use EXISTS:
SELECT EXISTS (SELECT 1 FROM users WHERE onduty = 1 AND loc_id = '{$site}') AS test;
Your original query would return "no row" if no row is found that matches the criteria. This one returns TRUE (1) or FALSE (0) every time.
In cases where there can be multiple rows matching the criteria and you are only interested whether at least one rows exists, performance of EXISTS is superior to a plain query. It can stop as soon as the first row is found and only returns 0 or 1.
db<>fiddle here
Old sqlfiddle
Use mysql_num_rows() to check number of rows returned on executing query.
$num_rows = mysql_num_rows($result);
if($num_rows==0)
{
//nothing returned
}
else
{
//rows returned
}
For corresponding mysqli implementation ,see mysqli_stmt_num_rows()

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