How to get the SQL_CALC_FOUND_ROWS value using prepared statements? - php

Question

I'm currently scratching my head at how to implement SQL_CALC_FOUND_ROWS with prepared statements.
I'm writing a pagination class and obviously i want to add LIMIT to the query but also find what the total number of rows would be.
Here's an example from the class in question.
$query = "select SQL_CALC_FOUND_ROWS id,title,location,salary,employer from jobs where region=38 limit 0,3";
if($stmt = $connection->prepare($query)) {
$stmt->execute()or die($connection->error); //execute query
$stmt->bind_result($id,$title,$location,$salary,$employer,$image);
while($stmt->fetch()){
$jobs[$x]['id']=$id;
$jobs[$x]['title']=$title;
$jobs[$x]['location']=$location;
$jobs[$x]['salary']=$salary;
$jobs[$x]['employer']=$employer;
$jobs[$x]['image']=$image;
$x++;
}
$stmt->close();//close statement
}
I'm a bit stumped as to how to get the SQL_CALC_FOUND_ROWS actual value? I had thought adding in something like:
$stmt->store_result();
$count=$stmt->num_rows;
But that only gives a number based on the LIMIT, so in the above example its 3 rather than the full 6 that it should be.

Answer 1

Managed to figure it out, i will detail my answer below for anyone whos interested in future.
Original Code
$query="select SQL_CALC_FOUND_ROWS id,title,location,salary,employer from jobs where region=38 limit 0,3";
if($stmt = $connection->prepare($query)) {
$stmt->execute()or die($connection->error); //execute query
$stmt->bind_result($id,$title,$location,$salary,$employer,$image);
while($stmt->fetch()){
$jobs[$x]['id']=$id;
$jobs[$x]['title']=$title;
$jobs[$x]['location']=$location;
$jobs[$x]['salary']=$salary;
$jobs[$x]['employer']=$employer;
$jobs[$x]['image']=$image;
$x++;
}
$stmt->close();//close statement
}
Updated Code
$query="select SQL_CALC_FOUND_ROWS id,title,location,salary,employer from jobs where region=38 limit 0,3";
if($stmt = $connection->prepare($query)) {
$stmt->execute()or die($connection->error); //execute query
$stmt->bind_result($id,$title,$location,$salary,$employer,$image);
while($stmt->fetch()){
$jobs[$x]['id']=$id;
$jobs[$x]['title']=$title;
$jobs[$x]['location']=$location;
$jobs[$x]['salary']=$salary;
$jobs[$x]['employer']=$employer;
$jobs[$x]['image']=$image;
$x++;
}
//get total number of rows.
$query="SELECT FOUND_ROWS()";
$stmt = $connection->prepare($query);
$stmt->execute();
$stmt->bind_result($num);
while($stmt->fetch()){
$count=$num;
}
$stmt->close();//close statement
}
Probably could do it better another way but couldn't seem to find any good examples anywhere online and this works!

Answer 2

If you want to get the result of SQL_CALC_FOUND_ROWS you need to run query SELECT FOUND_ROWS() in MySQL. To do that you don't need prepared statement. You can just use query() method.
$connection->query('SELECT FOUND_ROWS()')->fetch_row()[0];
If you are using mysqlnd, which you should be using if you are on one of the supported PHP versions, you can make your code much simpler.
// Enable error reporting instead of using or die($connection->error)
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
$query = "SELECT SQL_CALC_FOUND_ROWS id,title,location,salary,employer
FROM jobs
WHERE region=38
LIMIT 0,3";
$stmt = $connection->prepare($query);
$stmt->execute();
$jobs = $stmt->fetch_all(MYSQLI_ASSOC);
// There is no need for prepared statement when using FOUND_ROWS()
$connection->query('SELECT FOUND_ROWS()')->fetch_row()[0];
As you can see, it is much cleaner to use fetch_all() rather than while loop.
Warning
The SQL_CALC_FOUND_ROWS query modifier and accompanying FOUND_ROWS()
function are deprecated as of MySQL 8.0.17 and will be removed in a
future MySQL version. As a replacement, considering executing your
query with LIMIT, and then a second query with COUNT(*) and without
LIMIT to determine whether there are additional rows. For example,
instead of these queries:
SELECT SQL_CALC_FOUND_ROWS * FROM tbl_name WHERE id > 100 LIMIT 10;
SELECT FOUND_ROWS();
Use these queries instead:
SELECT * FROM tbl_name WHERE id > 100 LIMIT 10;
SELECT COUNT(*) WHERE id > 100;