I am having trouble with counting the rows in a table. I want to count how many rows there are where question_id is the same as $id. However, when I echo $total_records the result is just 1.
I'm expecting 21. I'm completely sure that the variables and database information is correct. Could anyone explain what I'm doing wrong?
$sqlwow="SELECT COUNT(a_id)
FROM forum_answer
WHERE question_id='$id'
ORDER BY a_id DESC";
$rsresult = $mysqli->query($sqlwow);
$row=$rsresult->fetch_assoc();
$total_records = count($row);
echo $total_records;
$sqlwow="SELECT COUNT(*)
FROM forum_answer
WHERE question_id='$id'
ORDER BY a_id DESC";
$rsresult = $mysqli->query($sqlwow);
$row = $rsresult->fetch_row();
$total_records = $row[0];
You shouldn't fetch as an associative result when all you have is one column. PDO actually has a shortcut for this using just fetchColumn to get the first column. MySQLi doesn't seem to have this shortcut so you can fetch the whole row as a numeric array then return the first result in that array (the first column) which will be the count.
You should also just use count(*) or count(1). Using a column name is slower as it doesn't check how many rows are returned, but how many non-null values of that column are returned. In most cases, this is the same, especially if that column is the primary key. Thanks for the clarification by #fthiella.
count($row) will always be 1. You need to alias your count in the SQL statement:
$sqlwow="SELECT COUNT(a_id) as num_records
FROM forum_answer
WHERE question_id='$id'
ORDER BY a_id DESC";
Then echo it as:
$total_records = $row['num_records'];
echo $total_records;
Related
if($sql = $db->query("Count (*) FROM post_items")){
echo mysqli_num_rows($sql);
}
what's wrong with my code? is this the correct way to echo the total of row in a table?
Your query should be
select count(*) FROM post_items
but echoing
mysqli_num_rows($sql);
will always give 1 as the ans, because count function returns only one row.
Rather fetch the details and show the count
$row = $sql->fetch_row();
echo $row[0];
No it is not; you will always get a return value of 1.
Why? Because you are in essence double-counting. The query executes a COUNT aggregate on the table returning a single row with the counted number. mysqli_num_rows is then counting the number of rows in this result set - the single row - and returns 1.
Try, the following line instead, which should fetch the first (only) column returned of the first (only) row in the result set.
echo $sql->fetch_row()[0]
Note you're also missing a SELECT keyword in your SQL statement.
It should be
if($sql = $db->query("select count(*) FROM post_items")){
echo mysqli_num_rows($sql);
}
I need to select category ids from my sql database.
I have a variable $product_id and for each product id there are three rows in a table that i need to select using PHP.
If I do "SELECT * FROM table_name WHERE product_id='$prodid'"; I only get the one on the top.
How can I select all three category_ids which contain the same product_id?
I suppose you are using PHP's mysql functions, is this correct? I am figuring that your query is actually returning all three rows but you aren't fetching all of them.
$sql = "SELECT * FROM table_name WHERE product_id='$prodid'";
$r = mysql_query($sql, $conn); //where $conn is your connection
$x = mysql_fetch_SOMETHING($r); //where something is array, assoc, object, etc.
The fetch function gives only one row at a time. You say you need three so it needs to be executed three times.
$x[0] = mysql_fetch_assoc($r);
$x[1] = mysql_fetch_assoc($r);
$x[2] = mysql_fetch_assoc($r);
OR this would be better
while($curRow = mysql_fetch_assoc($r)) //this returns false when its out of rows, returns false
{
$categoryIds[] = $curRow['category_id'];
}
If this doesn't do it then your query is actually returning only one row and we need to see your tables/fields and maybe sample data.
SQL seems to be correct, but Why do you store product_id in categories table? if it's one-to-many relation it would be better to store only category_id in products table.
The SQL query is correct for what you want to do. It will select all the records in table_name with the field product_id = $prodid (not only 1 or 3 but any that matches the variable)
To select a few records you should use the LIMIT keyword
You should look inside your table structure and the variable $prodid to find problems.
I want to fetch the last result in MySQL database table using PHP. How would I go about doing this?
I have 2 Columns in the Table, MessageID(auto) & Message.
I already know how to connect to the database.
Use mysql_query:
<?php
$result = mysql_query('SELECT t.messageid, t.message
FROM TABLE t
ORDER BY t.messageid DESC
LIMIT 1') or die('Invalid query: ' . mysql_error());
//print values to screen
while ($row = mysql_fetch_assoc($result)) {
echo $row['messageid'];
echo $row['message'];
}
// Free the resources associated with the result set
// This is done automatically at the end of the script
mysql_free_result($result);
?>
The SQL query:
SELECT t.messageid, t.message
FROM TABLE t
ORDER BY t.messageid DESC
LIMIT 1
...uses the ORDER BY to set the values so the highest value is the first row in the resultset. The LIMIT says that of all those rows, only the first is actually returned in the resultset. Because messageid is auto-increment, the highest value is the most recent one...
Records in a relational database do not have an intrinsic "order" so you cannot fetch the "last" record without some kind of ORDER BY clause.
Therefore, in order to fetch the "last" record, simply reverse the ORDER BY clause (change ASC to DESC or vice versa) then select the first result.
If you have an auto-increment field and you just want to find the last value that was inserted, you can use the fact that the auto-increment fields are ever-increasing (therefore the "last" one will be the one with the highest value) and do something like this:
SELECT *
FROM my_table
ORDER BY id_field DESC
LIMIT 1
Of course you can select the last row by sorting DESC in your query. But what if you want to select the first row and then the last. You can run a new query, but you can also use the function mysql_data_seek. check code below:
$result = mysql_query('YOUR QUERY') or die('Invalid query: ' . mysql_error());
$row_first = mysql_fetch_array($result);
mysql_data_seek($result , (mysql_num_rows($result)-1));
$row_last = mysql_fetch_array($result);
Hope this helps
The MySql query would look like this:
select MessageID, Message
from Table
order by MessageID desc
limit 1;
I am too rusty with PHP to give you the right syntax for executing this.
This query works because you have an auto-incrementing identifying field (MessageID). By ordering the results by that field in descending (largest to smallest) order we are effectively returning the records in the table in reverse order. The limit 1 clause simply limits the result set to one record - the last one in the table.
What do you mean by "the last result"? You need to precise a bit more.
Do you mean "the last entry I registered"?
In this case you should use the appropriate method (depending on the extension you are using) mysqli->insert_id OR mysql_insert_id.
If you mean "the latest entry in the table", an SQL query such as Andrew Hare's is just what you need.
Do you mean the last record or do you need the id of the most recently inserted record? For that you would use the PHP mysql_insert_id() function. Or if you are using the myusqli extension use $mysqli->insert_id.
for some reason (which I don't know why), my boss force me to get the data in this way:
$message_arr = array();
while ($row = mysql_fetch_assoc($result)) {
$message_arr['messageid']= $row['messageid'];
$message_arr['message']= $row['message'];
}
return $message_arr;
Of course, you need everything from OMG Ponies's answer I'm just telling you another way to do it =)
I hope this help.
You should use SELECT query. How SELECT works.
SELECT * FROM table - selects everything in a table (id, row 1, row 2,...)
SELECT id FROM table - selects only particular row from table.
If you now know, how to select, you can use additional logic.
SELECT * FROM table ORDER by id DESC LIMIT 1;
selects everything from table table, orders it by id - orders it DESCENDING and limits the query to only one result.
If you would do it like this:
SELECT * FROM table ORDER by id ASC limit 1; - you would get 1 entry into database.
You can order it by any row you want.
Hope it helps.
One thing to remember is that data does not get saved in the insertion order in any MYSQL database. So in order to get the last entered record u will have to have an auto increment field. Since there is an auto increment field in this table we are good to go.
The below script will help to get the last entered record
<?php
$sql = "SELECT * FROM table_name ORDER BY MessageID DESC LIMIT 2";
$result_set = mysql_query($sql);
if($result_set){
while($row = mysql_fetch_array($result_set)) {
echo "Message Id: ".$row['MessageID']."<br>";
echo "Message: ".$row['Message']."<br>";
}
//creating alert
echo "<script type=\"text/javascript\">alert('Data was Retrieved
successfully');</script>";
}
else{
//creating alert
echo "<script type=\"text/javascript\">alert('ERROR! Could Not Retrieve
Data');</script>";
}
?>
The query selects all the records in the table and orders them according to the descending order of the MessageID (as it is the auto increment field) and limits the returned result to only one record. So since the table is ordered according to the descending order of the MessageID only the last entered record will be returned.
NOTE: if you are using a newer version you will have to use mysqli_query($connection_variable,$sql); instead of mysql_query($sql); and mysqli_fetch_array($result_set) instead of mysql_fetch_array($result_set)
$result = mysql_query('select max(id) from your_table ') or die('Invalid query: ' . mysql_error());
while ($row = mysql_fetch_assoc($result)) {
echo $row['id'];
echo $row['message'];
}
//
//
mysql_free_result($result);
simple like that
this code of php works fine
SELECT t.messageid, t.message
FROM TABLE t
ORDER BY t.messageid DESC
LIMIT 1
if you don't have concurrent entries going into some table.b'cause concurrent entries may not go in accordance of their insertion order.
$statement = $PDO->prepare("
SELECT MessageID,
Message
FROM myTable
ORDER BY MessageID DESC
LIMIT 1;
");
$statement->execute();
$result = $statement->fetch(\PDO::FETCH_ASSOC);
echo $result['MessageID']." and ".$result['Message'];
If I need to know the total number of rows in a table of database I do something like this:
$query = "SELECT * FROM tablename WHERE link='1';";
$result = mysql_query($query);
$count = mysql_num_rows($result);
Updated: I made a mistake, above is my actual way. I apologize to all
So you see the total number of data is recovered scanning through the entire database.
Is there a better way?
$query = "SELECT COUNT(*) FROM tablename WHERE link = '1'";
$result = mysql_query($query);
$count = mysql_result($result, 0);
This means you aren't transferring all your data between the database and PHP, which is obviously a huge waste of time and resources.
For what it's worth, your code wouldn't actually count the number of rows - it'd give you 2x the number of columns, as you're counting the number of items in an array representing a single row (and mysql_fetch_array gives you two entries in the array per column - one numerical and one for the column name)
SELECT COUNT(*) FROM tablename WHERE link='1';
You could just do :
SELECT count(*) FROM tablename;
for your query. The result will be a single column containing the number of rows.
If I need to know the total number of rows in a table of database
Maybe I'm missing something here but if you just want to get the total number of rows in a table you don't need a WHERE condition. Just do this:
SELECT COUNT(*) FROM tablename
With the WHERE condition you will only be counting the number of rows that meet this condition.
use below code
$qry=SHOW TABLES FROM 'database_name';
$res=mysql_query($qry);
$output=array();
$i=0;
while($row=mysql_fetch_array($res,MYSQL_NUM)){
++$i;
$sql=SELECT COUNT(*) FROM $row[0];
$output[$i]=mysql_query($sql);
}
$totalRows=array_sum($ouptput);
echo $totalRows;
http://php.net/manual/en/function.mysql-num-rows.php You need this i think.
If you are going to use the following SQL statement:
SELECT COUNT(*) FROM tablename WHERE link='1';
Make sure you have an index on the 'link' column
I'm trying to fetch random no. of entries from a database by using
SELECT QNO FROM TABLE ORDER BY RAND() LIMIT 10
it returns a column of database.
If I want to save all the entries in a array, then which php function do I have to use to save the column.
Something along the lines of this?
$result = mysql_query("SELECT QNO FROM TABLE ORDER BY RAND() LIMIT 10");
$rows = array();
while ($row = mysql_fetch_row($result)) {
$rows[] = $row[0];
}
Updated to not use the $i variable as pointed out in the first post and the comment.
Look at some examples for how to run a query and get a result set.
http://www.php.net/mysqli
Once you have the result in a variable, do this:
$myarray = array();
while($row = mysqli_fetch_row($result))
$myarray[] = $row[0];
With PDO:
$qryStmt = $dbc->query('SELECT QNO FROM TABLE ORDER BY RAND() LIMIT 10');
$a = $qryStmt->fetchAll( PDO::FETCH_COLUMN );
BTW: If you just want to get one row by random, this is much faster esp. for large tables:
select * from table limit 12345,1;
where 12345 is just a random number calculated from the count() of rows.
see here, which is more for rails, but have a look at the comments too.
But be careful: in limit 12345,2 - the second row is not random but just the next row after the random row. And be careful: When I remember right (eg. SQLServer) rand() could be optimized by databases other than mysql resulting in the same random number for all rows which makes the result not random. This is important, when your code should be database agnostic.
a last one: do not mix up "random" with "hard to predict", which is not the same. So the order by example "select top 10 ... order by rand()" on SQLServer results in two different result sets when run twice, BUT: if you look at the 10 records, they lie close to each other in the db, which means, they are not random.