PHP select multiple tables from MYSQL - php

Question

I'm beginner at PHP & MYSQL I don't know where is the error at this code first MySQL database contains 6 tables I've no equation to JOIN them together and I want to show the last added value of each table
<?php
$servername = "localhost";
$username = "project";
$password = "pro2018";
$dbname = "project";
$conn = new mysqli($servername, $username, $password, $dbname);
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}
$sql_temp = "select * from temp order by id desc limit 1 ";
$sql_hum = "select * from hum order by id desc limit 1 ";
$sql_soil1 = "select * from soil1 order by id desc limit 1 ";
$sql_soil2 = "select * from soil2 order by id desc limit 1 ";
$sql_soil3 = "select * from soil3 order by id desc limit 1 ";
$sql_soil4 = "select * from soil4 order by id desc limit 1 ";
$result_temp = $conn->query($sql_temp);
$result_hum = $conn->query($sql_hum);
$result_soil1 = $conn->query($sql_soil1);
$result_soil2 = $conn->query($sql_soil2);
$result_soil3 = $conn->query($sql_soil3);
$result_soil4 = $conn->query($sql_soil4);
//if ($result_->num_rows > 0) {
// output data of each row
$row_temp = $result_temp->fetch_assoc()) ;
$row_hum = $result_hum->fetch_assoc()) ;
$row_soil1 = $result_soil1->fetch_assoc()) ;
$row_soil2 = $result_soil1->fetch_assoc()) ;
$row_soil3 = $result_soil1->fetch_assoc()) ;
$row_soil4 = $result_soil1->fetch_assoc()) ;
$x = $row_temp["value"];
$y = $row_hum["value"];
$a = $row_soil1["value"];
$b = $row_soil2["value"];
$c = $row_soil3["value"];
$d = $row_soil4["value"];
echo " $x" . " Degree";
echo " $y" . " %";
echo " $a" . " %";
echo " $b" . " %";
echo " $c" . " %";
echo " $d" . " %";
header("Refresh:5");
?>

Answer 1

Welcome to Stack overflow!
First off, consider using PDO objects in PHP. PDO are the latest way to talk to databases in PHP. It is a more generalized platform that can talk to many more diffrent types of database. PHP manual here. Outline of differences between MySqli and PDO here(external).
Second, without joining, you can't return the data from more than one table at a time in one SQL SELECT statement. You will need to do multiple requests, as you have in your code example.
You could make the process more streamlined, though, by having an array of the tables you want to get data from:
$tableArray = array(
'tableOne'=>"<name of table one>",
'tableTwo'=>"<name of table two>",
...
);
$resultArray = array();
//get results from server
foreach($tableArray as $curKey=>$curTable){
//ONLY SAFE IF $tableArray IS NEVER CHANGED
$curStmt = "SELECT * FROM ".$curTable." order by id desc limit 1;";
$resultArray[$curKey] = //set this to the result from the sql statement
}
//print them out
foreach($resultArray as $curKey=>$curValue){
echo $curKey. " " . $curValue;
}
This method lets you setup the tables you want to get the info from in one place and do everything you need for you.
Make sure that your list of table names can never be edited though (just never assign it beyond the initial definition). Unfortunately, you cannot use a table name as a parameter for prepared statements, so you must build the sql statements yourself (as shown in my example), opening up the possibility for SQL injection. If you never assign the values of your table array outside of the initial definition, you should be fine though.
( I know the link explaining that tables as parameters doesn't work is specifically for java, but the issue there is SQL querying, not Java based)