PHP SQL-从一个表中选择多个

Question

I have a SELECT query from one table that works great as follows:

 $sql = "SELECT count(max720) AS anzahlpositive1 from table where (((max720 - lastsignal)/lastsignal)*100) >= 1 AND (((max720 - lastsignal)/lastsignal)*100) < 2 AND max720 != ''";
$result = $conn->query($sql);

But I had 20-30 of them with other values. For every SELECT query a new connection established.. I think thats a lot of perfomance.

Thats the 2nd:

$sql = "SELECT count(max720) AS anzahlpositive2 from table where (((max720 - lastsignal)/lastsignal)*100) >= 2 AND (((max720 - lastsignal)/lastsignal)*100) < 3 AND max720 != ''";
$result = $conn->query($sql);

Is is possible to do this in ONE select? (better performance)

I have tried with UNION (but i think its for 2 or more tables)

Is that a solution?

$sql = "SELECT 1";
$sql .= "SELECT 2";
$sql .= "SELECT 3";
...

$result = $conn->query($sql);
while($row = $result->fetch_assoc()) {
echo $anzahlpositive1 ;
echo $anzahlpositive2 ;
echo $anzahlpositive3 ;
....
}

Answer 1

select  count(max720) AS ...
union all
select  count(max720) AS ...

You can use as many unions as you want, read the difference between union and union all , union will discard duplicates.