左联接工作不正常

Question

I need some help with LEFT Join

first db is "fpo"

id----empnum-----amount---date----ponum

second db is "users"

id----amount-----empid----username----password

I need to total the "amount" in fpo for each user and compare the total to the amount from users.

This is the code i have now that is NOT working.

 $result = mysqli_query($con,
 "select fpo.amount , fpo.empnum , user.amount , user.fpo SUM(amount) 
  FROM LEFT JOIN fpo ON fpo.empnum = users.empnum GROUP BY empnum");

while($row = mysqli_fetch_array($result)) {
  echo $row['empnum'];
  echo "<br>";
  echo $row['amount'];
}

For some reason this is not working.... What am i doing wrong i have never worked with JOIn command.

Here is what the data looks like in mysql

**first db is "fpo"**
id----empnum-----amount-----date-------ponum
1-----854245-----5.00------9/7/14------12345
2-----123987-----8.00------9/7/14------12345
3-----123987-----5.00------9/7/14------12345
4-----854245-----15.00-----9/7/14------12345
5-----548798-----10.00-----9/7/14------12345
6-----854245-----30.00-----9/7/14------12345

**second db is "users"**
id----amount-----empid----username----password
1-----700.00-----854245---admin-------abc123
2-----500.00-----123987---admin-------abc123
3-----200.00-----548798---admin-------abc123

What i am trying to do is sum(amount) From fpo where empnum (note:from fpo) = empnum (note:from users) then echo the summed amount with the empnumber and the amount from the users table.

I need to do this for everyone in the users db. I have about 150 people in there right now.....

Thank you for your time and help!!! Probably a simple problem :(

Answer 1

You're not echoing the summed amount, $row['amount'] is the amount of a single row, you want $row['SUM(amount)'] . I suggest you give it an alias to make it easier to access:

$result = mysqli_query($con,"select f.amount , u.empid , u.amount , 
                                u.fpo, SUM(u.amount) AS total
                             FROM users AS u
                             LEFT JOIN fpo AS f ON f.empnum = u.empid
                             GROUP BY u.empid") or die(mysqli_error($con));

while($row = mysqli_fetch_array($result)) {
      echo $row['empnum'];
      echo "<br>";
      echo $row['total'];
}

You were also missing the comma before SUM(amount) , the table name after FROM , and you need to qualify amount with the table name because both tables have a column named amount . You also had user.empnum in your ON clause, but that column is users.empid .

You should select and group by the column from users , not fpo , because LEFT JOIN can return rows where the columns from fpo are NULL if there's no match for users.empid .

Answer 2

This seems to work for me. Thanks!

    result = mysqli_query($con,"select f.amount , u.empnum , u.amount , 
                                SUM(f.amount) AS total
                             FROM users AS u
                             LEFT JOIN fpo AS f ON f.empnum = u.empnum
                             GROUP BY u.empnum")

                              or die(mysqli_error($con));

while($row = mysqli_fetch_array($result)) {
      echo "Emp".$row['empnum']."----".$row['total']."----Amount----".$row['amount']."<br>";