When I want to find out how many shoes Alfred has, I always count the rows in the table "usershoes" where the userid matches Alfred's
But since I switched to PDO, and select row count is not simple or bulletproof/consistent, I'm reconsidering my methods
Maybe I should instead keep an int field "shoes" directly in table "users", keep number of shoes there, and then increase/decrease that number for that user along the way? Feels not right..
If anyone has a solid method for simple row counting on an existing select query, without extra query, let me know
Try something like this
SELECT COUNT(*) FROM usershoes
WHERE userid="theIdOfTheUser";
I could not get count(fetchColumn()) or fetchColumn() to work correctly (outputted 1 when 0 was the real number)
So now I'm using this, and it works:
$sql = 'SELECT COUNT(*) as numrows, shoecolor FROM usershoes WHERE userid = ?'
$STH = $conn->prepare($sql);
$STH->execute(array($someuseridvar));
And then:
$row = $STH->fetch();
if ($row['numrows'] > 0) {
// at least one row was found, do something
}
With MySQL, you can use FOUND_ROWS():
$db = new PDO(DSN...);
$db->setAttribute(array(PDO::MYSQL_USE_BUFFERED_QUERY=>TRUE));
$rs = $db->query('SELECT SQL_CALC_FOUND_ROWS * FROM table LIMIT 5,15');
$rs1 = $db->query('SELECT FOUND_ROWS()');
$rowCount = (int) $rs1->fetchColumn();
$rowCount will contain the total number of rows, not 15.
Taken from:
http://php.net/manual/en/pdostatement.rowcount.php#83586
Related
Here's my usual way of counting rows...
$query = "SELECT * FROM users";
$stmt = $db->prepare($query);
$stmt->execute();
$count = $stmt->rowCount();
This will count all rows, even if I use a WHERE clause, it'll still count every row that meets that condition. However, let's say I have a table, we'll call it tokensEarned (that's my actual table name). I have the following data...
user_id = 1,2,4,5,8,8,2,4,3,7,6,2 (those are actual rows in my table - clearly, user 1 has 1 entry, 2 has three entries, etc.) In all, I have 12 entries. But I don't want my query to count 12. I want my query to count each user_id one time. In this example, my count should display 8.
Any help on this? I can further explain if you have any specific questions or clarification you need. I would appreciate it. Thank You.
The following query will yield the distinct user count:
$query = "SELECT COUNT(DISTINCT user_id) AS cnt FROM users";
$stmt = $db->prepare($query);
$stmt->execute();
$row = $stmt->fetch(PDO::FETCH_ASSOC);
echo "distinct user count: " . $row['cnt'];
It isn't possible to get all records and the distinct count in a single query.
Whether you use the query above or you return all the actual distinct rows really depends on whether you need the full records. If all you need are the counts, then it is wasteful to return the data in the records, and what I gave above is probably the best option. If you do need the data, then selecting all distinct rows might make more sense.
You can use distinct in mysql to select only unique fields in your table.
$query = "SELECT distinct user_id FROM users";
$stmt = $db->prepare($query);
$stmt->execute();
$count = $stmt->rowCount();
Change your query to the following, this way you only shows the unique user_id:
$query = "SELECT DISTINCT user_id FROM users";
If I have a table with 3 rows with IDs 1,3,5 because rows with ID 2 and 4 were deleted, how do I make sure I select a row that exists?
$stmt = $db->prepare("SELECT COUNT(*) FROM table");
$stmt->execute();
$stmt->bind_result($numRows);
$stmt->fetch();
$stmt->close();
$random = mt_rand(1,$numRows);
$stmt = $db->prepare("SELECT link FROM table WHERE id=$random");
This won't ever select row with id 5, and also will select one that doesn't exist (2).
If the number of rows are small (and you are sure that it will stay that way), you can use ORDER BY RAND()
(Please note that this will create performance problems with big tables).
Other way is first counting how many rows are there
SELECT COUNT(*) AS total FROM table;
then pick a random number
$rand = rand(1, $total);
and select that row with limit
SELECT * FROM table LIMIT $rand, 1;
U can use a SQLstatement with EXISTS
SELECT link
FROM table
WHERE EXISTS (SELECT link
FROM table
WHERE id = $random);
If you just want a random row and don't care about the id, then you could use:
SELECT link FROM table
ORDER BY RAND()
LIMIT 1
For large numbers of rows (10000+), then you may need to implement another solution, as this query can be slow. This site has a good explanation and alternative solutions
If you want to follow your approach then you have to do some changes in your query.
1.) Query one : select id from table. // It will give you array of existing id.
2.) You have to use array_rand(). and use your second query.
Example :
$stmt = $db->prepare("SELECT ID FROM table");
$result = $stmt->fetchAll();
$random = array_rand(array_flip($result), 1);
$stmt = $db->prepare("SELECT link FROM table WHERE id=$random");
You could select one, randomly order, like this:
SELECT link FROM table ORDER BY RAND() LIMIT 1
UPDATE:
You should benchmark the different solutions you have, but I'm thinking this one could be nice with large amount of rows:
$stmt = $db->prepare("SELECT COUNT(*) FROM table");
$stmt->execute();
$stmt->bind_result($numRows);
$stmt->fetch();
$stmt->close();
$random = mt_rand(1,$numRows);
$stmt = $db->prepare("SELECT link FROM table WHERE id>=$random LIMIT 1");
$stmt->execute();
$stmt->bind_result($link);
if(!$link){
$stmt = $db->prepare("SELECT link FROM table WHERE id<$random LIMIT 1");
$stmt->execute();
$stmt->bind_result($link);
}
I have the following query.
$sql = "SELECT customer FROM furniture WHERE id = :id AND category = :cat";
$stmt = $connectdb->prepare($sql);
$stmt->execute(array(':id'=>$id, ':cat'=>"1"));
$resulta = $stmt->fetchAll(PDO::FETCH_ASSOC);
$rowcount = count($result);
This works perfectly. But I have a requirement to get the number of rows from WHERE id = :id AND category = :cat as well as to get the number of rows from WHERE category = :cat. Is it possible to do both of them without having to write all those SELECT query lines twice?
You can use conditional sum to get the 2 different counts something as
select
sum(id = :id AND category = :cat) as count1,
sum(category = :cat) as count2
from furniture;
Later you just fetch the records and get the values of count1 and count2
NOTE : If you just do row count it will always return 1 since its using the aggregate function
I would suggest that you write the query as:
select sum(id = :id) as numCatId, count(*) as numCat
from furniture
where cat = :cat;
Putting the condition in the where clause allows MySQL to use an index on furniture(cat) (or better yet furniture(cat, id). In general, it is a good idea to put common filtering conditions in the where clause. This reduces the number of rows needed for processing the rest of the query.
If I run a query that returns multiple rows, is there a way I can select just one row out of that result?
So if I do something like
SELECT * FROM table WHERE number = 10
and it returns 33 results, is there a way I can go through those one at a time instead of returning the whole result set at once, or just return, for example, row 5 of the result set?
I have read about scrollable cursors but it seems they don't work on MySQL, although that seems to be what I am looking for....
I am using PDO with MySQL and PHP. I hope this makes sense, if not I will try and explain better.
Edit: This worked for what I wanted. Thanks.
$stmt = $dbh->prepare("SELECT * FROM $table WHERE user_points = '$target' ORDER BY tdate DESC LIMIT $count,1");
is there a way I can select just one row out of that result?
Yes there is, you can use LIMIT:
SELECT * FROM table WHERE number = 10 LIMIT 1;
$sql= "SELECT * FROM $table WHERE user_points = '$target' ORDER BY tdate";
$stmt= $pdo -> prepare($sql);
$stmt->execute();
$data = $stmt ->fetchAll();
//You asked about getting a specific row 5
//rows begin with 0. Now $data2 contains row 5
$data2 = $data[4];
echo $data2['A_column_in_your_table'];//row 5 data
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.