I want to count the results in my table... but I am usually confronted with a decision, what column do I select? Should I select the primary key? Wild Card? What has the most performance? Does it matter? Below is an example of how I call it
// Wild Card, I feel like this is the worst one for performance?
$query = "SELECT * FROM table WHERE status = ?";
// Only selecting one column? Is there a better way
$query = "SELECT id FROM table WHERE status = ?";
$stmt = $mysqli->prepare($query);
$stmt->bind_param('i',$status);
$stmt->execute();
$stmt->store_result();
$returned_amount = $stmt->num_rows;
$stmt->free_result();
$stmt->close();
Well, if you want MySQL to handle the count, you can just do the following
$query = "SELECT COUNT(*) as count FROM `table` WHERE `field` = ?";
The as count part means that you can access the count as if it were a column.
You should SELECT COUNT(`id`) FROM `table` WHERE `status`=?, much more efficient ;)
If you are willing to count all the results of your query (ie: for pagination), you can use FOUND_ROWS() option:
In your main query you need to add SQL_CALC_FOUND_ROWS option just after SELECT and in second query you need to use FOUND_ROWS() function to get total number of rows.
SELECT SQL_CALC_FOUND_ROWS id FROM table WHERE status = 'something' LIMIT 10;
SELECT FOUND_ROWS();
More info in dev.mysql.com
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);
}
how would i go about ordering by a value that is not in the table where i am selecting from, in this instance the value $count1 is not in the table search.
count has the same identifying id as that of the thing it is being reffered to in the other table, this is where count1 is grabbed
$q = $db->prepare("SELECT COUNT(rating) FROM ratings WHERE id='$id' AND rating = 'd'");
$q->execute();
$count1 = $q->fetchColumn();
$query = "SELECT * FROM search WHERE title LIKE '$each' ORDER BY '$count1'"
$query = $db->prepare($query);
$query->execute();
that is from ratings, how would i go about ordering the entries like that, so that they are based off the number of count1 and are decided, i might have to implement something like
$query = "SELECT * FROM search WHERE title LIKE '$each' AND id = '$id' ORDER BY '$count1'"
$query = $db->prepare($query);
$query->execute();
Possible Duplicate: Mysql order by specific ID values
Same thing here, you'll just output your $count1as a comma separated string and add it in the SQL query as ORDER BY FIELD(COUNT,___comma_sep_string___)
ratings is a table, not a database. You can join tables or use subqueries to get the desired result, without having to make multiple queries.
You haven't described how the FOREIGN_KEY is set up in the ratings table, but assuming you have something ratings.search_id, this should work:
SELECT search.*, (SELECT COUNT(rating)
FROM ratings
WHERE ratings.search_id = search.id
AND rating = 'd'
) AS rating_count
FROM search
WHERE title LIKE '$each'
ORDER BY rating_count
I want to fetch the total count of records in MySQL db table and also use the limit with this. For example, there are 100 rows and the limit I want to use let suppose is 10. I know how to do this using two queries but I want to do this in one go.
SELECT count(*) as total_rows FROM mytable; // gets the total count of rows
SELECT col1,col2 FROM mytable LIMIT 0, 10; // gets the 10 rows of col1,col2
I want to do this in one go. Any idea.
Thanks.
Here is the SQL Fiddle that demonstrates how the below works:
SELECT m.*,
(
SELECT COUNT(*)
FROM mytable AS sm
) AS TotalCount
FROM (
SELECT mt.col1, mt.col2
FROM mytable AS mt
LIMIT 0, 10
) AS m
Have a look at Shayan Husaini's answer on How to get the total row count with MySQLi
I have updated his original answer after trying it out myself. You have to add "SQL_CALC_FOUND_ROWS" after SELECT in your query and add a second query as shown in the code snippet below.
$sql1 = "SELECT SQL_CALC_FOUND_ROWS col1,col2 FROM mytable LIMIT 0, 10";
$sql2 = "SELECT FOUND_ROWS()";
$result1 = $conn->query($sql1);
$result2 = $conn->query($sql2);
$TotalRcount = $result2->fetch_row();
// I have added this next line to correct the answer
$TotalNumRows = $TotalRcount[0];
You can use $result1 to access your results as you normally would.
I have a SQL Query, although it is executing, but how should i verify if it is giving me the desired result.
For example: My query
$query3 = "SELECT COUNT(DISTINCT(uid)) AS `num`
FROM `user_info`
WHERE date(starttime)='2011-10-10'";
In the above query i am trying to count the number of distinct user ID's(uid) from the table named user-infowhere date is 2011-10-10.
How should i display the count which is calculated for the given date?.I need to know it and perform some further operations on it!
$query3 = "SELECT COUNT(DISTINCT uid) AS `num`
FROM `user_info`
WHERE date(starttime)='2011-10-10'";
$result = mysql_query($query3);
$row = mysql_fetch_array($result);
echo $row['num'];
Just do:
SELECT COUNT(DISTINCT uid) AS `num`
FROM `user_info`
WHERE date(starttime)='2011-10-10'
This SO post goes into some details about how count and count(distinct ...) work. With just count, there is a hidden/assumed function of count(all ... ) actually happening (it's just the default value). If you want to only count distinct things, switch it to the non-default and do the count(distinct ...) instead. I didn't know it existed for my first 6 months of writing sql or so...
You can set a variable sing the result...
SET #userVar=SELECT
COUNT(DISTINCT uid)
FROM
user_info
WHERE
DATE(starttime)='2011-10-10';
Then you can use that variable in your next operation or query.