mysqli count rows php
mysqli_stmt::$num_rows
mysqli_stmt_num_rows
Описание
Возвращает количество строк, помещённых в буфер в выражении. Функция будет работать только после вызова mysqli_stmt_store_result() для буферизации всего набора результатов в дескрипторе оператора.
Список параметров
Возвращаемые значения
Целое число ( int ), представляющее количество буферизованных строк. Возвращает 0 в небуферизованном режиме, если с сервера не были получены все строки.
Примеры
Пример #1 Объектно-ориентированный стиль
Пример #2 Процедурный стиль
Результат выполнения данных примеров:
Смотрите также
User Contributed Notes 1 note
Please be advised, for people who sometimes miss to read this important Manual entry for this function:
If you do not use mysqli_stmt_store_result( ), and immediatley call this function after executing a prepared statement, this function will usually return 0 as it has no way to know how many rows are in the result set as the result set is not saved in memory yet.
mysqli_stmt_store_result( ) saves the result set in memory thus you can immedietly use this function after you both execute the statement AND save the result set.
If you do not save the result set but still want to use this function you have to actually loop through the result set one row at a time using mysqli_stmt_fetch( ) before using this function to determine the number of rows.
A thought though, if you want to determine the number of rows without storing the result set and after looping through it, why not just simply keep an internal counter in your loop every time a row is fetched and save the function call.
In short, this function is only really useful if you save the result set and want to determine the number of rows before looping through it, otherwise you can pretty much recreate its use like I suggested.
mysql_num_rows
mysql_num_rows — Возвращает количество рядов результата запроса
Данный модуль устарел, начиная с версии PHP 5.5.0, и удалён в PHP 7.0.0. Используйте вместо него MySQLi или PDO_MySQL. Смотрите также инструкцию MySQL: выбор API. Альтернативы для данной функции:
Описание
Список параметров
Возвращаемые значения
Количество рядов в результате запроса в случае успешного выполнения или false в случае возникновения ошибки.
Примеры
Пример #1 Пример использования mysql_num_rows()
Примечания
При использовании mysql_unbuffered_query() функция mysql_num_rows() не вернёт корректного значения до тех пор, пока все ряды не будут получены.
Для обратной совместимости может быть использован следующий устаревший псевдоним: mysql_numrows()
Смотрите также
User Contributed Notes 22 notes
Some user comments on this page, and some resources including the FAQ at :
This is not a particularly universal solution, and those who read these comments on this page should also be aware that
select count(*) may not give correct results if you are using «group by» or «having» in your query, as count(*) is an agregate function and resets eachtime a group-by column changes.
can be an alternative to sub-selects in mysql 3, and such queries cannot have the select fields replaced by count(*) to give good results, it just doesn’t work.
*Early detection of invalid constant expressions. MySQL quickly detects that some SELECT statements are impossible and returns no rows.
*All constant tables are read first, before any other tables in the query. A constant table is:
1) An empty table or a table with 1 row.
2) A table that is used with a WHERE clause on a UNIQUE index, or a PRIMARY KEY, where all index parts are used with constant expressions and the index parts are defined as NOT NULL.
Hopefully this will keep someone from staying up all night with 1146 errors, unless I am completely mistaken in thinking I have this figured out.
This seems the best workaround to get an ‘ordinary’ loop going, with possibility of altering output according to row number
(eg laying out a schedule)
In response to oran at trifeed dot com:
You are only experiencing this behaviour because you have not given your FOUND_ROWS() result an alias:
SELECT SQL_CALC_FOUND_ROWS together with
SELECT FOUND_ROWS()
After all there is an array of row arrays, as signified by
mysql_num_rows($result):
Say this gives «40 rows» : it would be useful to know when the iteration is on row 39.
The nearest seems to be «data seek»:but it connects directly to a
row number eg (from mysql_data_seek page)
= it still wouldn’t solve knowing what row number you’re on in an ordinary loop.
One reason for this situation is the php fetch (fetch-a-single-row) construction, without any reasonable FOR loop possibility with row numbers.
Suggestion:
$Rows[$i] possibility where
$i would be the row number
A note on the following usage; that suggest to use several MySQL Functions to get the number of Table Records.
You may be familiar with following:
= ‘Select SQL_CALC_FOUND_ROWS `MyField` From `MyTable` Limit 1;’ ;
$sqlQuery_1 = ‘Select FOUND_ROWS( );’ ;
?>
I omitted the actual connection to MySQL and the execution of the query, but you get the idea.
I did some tests and on a fairly high traffic web site, one that executes several queries quite often and found that using this combination of MySQL Functions can actually result in wrong results.
For example, assume I have two queries to get the number of Table Records in two different Tables. So in essence, we are executing 4 queries ( 2 queries for each Table ).
If two different requests come in through PHP, your going to run into problems. Note than when I mean request, I mean two different clients requesting your PHP page.
Execute: SQL_CALC_FOUND_ROWS On Table 1
Execute: SQL_CALC_FOUND_ROWS On Table 2
Execute: Select FOUND_ROWS( )
At this point, you see the race condition that occurred. While Request 1 was being executed, Request 2 came in.
At this point Request 1 will return the number of Table Records in Table 2 and not Table 1 as expected!
Why? Because MySQL does not differ between requests. Each query is in a queue waiting its turn. As soon as its turn comes in it will be executed my MySQL.
The MySQL Function Select FOUND_ROWS( ) will return the result of the last SQL_CALC_FOUND_ROWS!
MySQL 4.0 supports a fabulous new feature that allows you to get the number of rows that would have been returned if the query did not have a LIMIT clause. To use it, you need to add SQL_CALC_FOUND_ROWS to the query, e.g.
$sql = «Select SQL_CALC_FOUND_ROWS * from table where state=’CA’ limit 50»;
$result = mysql_query($sql);
$sql = «Select FOUND_ROWS()»;
$count_result = mysql_query($sql);
You now have the total number of rows in table that match the criteria. This is great for knowing the total number of records when browsing through a list.
To use SQL COUNT function, without select the source.
In preventing the race condition for the SQL_CALC_FOUND_ROWS and FOUND_ROWS() operations, it can become complicated and somewhat kludgy to include the FOUND_ROWS() result in the actual result set, especially for complex queries and/or result ordering. The query gets more complex, you may have trouble isolating/excluding the FOUND_ROWS() result, and mysql_num_rows() will return the number of actual results + 1, all of which makes your code messier and harder to read. However, the race condition is real and must be dealt with.
A alternative and cleaner method is to explicitly lock the table using a WRITE lock (preventing other processes from reading/writing to the table). The downsides I can see are a performance hit, and your mysql user must have lock permissions.
// excuse the use of mysqli instead of mysql
Actually I am a little ashamed to be saying this, but I stand corrected about a rather old note I posted on 17-Jul-2007 06:44.
Using SQL_CALC_FOUND_ROWS and FOUND_ROWS( ) will NOT trigger a race condition on MySQL, as that would pretty much defy their entire purpose.
The results for their usage is actually unique per connection session as it is impossible for processes to share anything in PHP. As far as PHP is concerned, each request represents a new connection to MySQL as each request is isolated to its own process.
To simulate this, create the following script:
?>
Set the connection and query information for something that matches your environment.
Run the script once with the Sleep query string and once again without it. Its important to run them both at the same time. Use Apache ab or something similar, or even easier, just open two browser tabs. For example:
If a race condition existed, the results of the first instance of the script would equal the results of the second instance of the script.
For example, the second instance of the script will execute the following SQL query:
( «SELECT SQL_CALC_FOUND_ROWS `aid` From `access` Limit 1» );
?>
This happens while the first instance of the script is sleeping. If a race condition existed, when the first instance of the script wakes up, the result of the FOUND_ROWS( ) it executes should be the number of rows in the SQL query the second instance of the script executed.
But when you run them, this is not the case. The first instance of the script returns the number of rows of its OWN query, which is:
( «SELECT SQL_CALC_FOUND_ROWS `bid` From `blocks` Limit 1» );
?>
So it turns out NO race condition exists, and every solution presented to combat this «issue» are pretty much not needed.