参照完整性错误

Question

I am having a bit of trouble with referential integrity errors on my database final exam project. I have tried to figure it out myself, but to no avail, and I am hoping someone here can point me in the right direction.

The problem is that I have three tables with the first two being parent tables to the third table. I am trying to construct a php script that will update the two parent tables and then insert the data into the child table. What I have thus far, I thought would work, but whenever I try to use it, I get the following error:

INSERT INTO Purchases (CustomerID, PurchaseOrderNo, PurchaseTotal, DateOfPurchase, SalesPersonID,SpecialOrder) VALUES ('10', '0000','100.00','0000-00-00','5555','N')

Cannot add or update a child row: a foreign key constraint fails ('xxxxxx'.'Purchases', CONSTRAINT 'Purchases_ibfk_1' FOREIGN KEY ('CustomerID') REFERENCES 'CustomerInfo'('CustomerID') ON DELETE CASCADE ON UPDATE CASCADE)'

Any thoughts where I have gone wrong?

        ########## FOREIGN KEY CHECK START ##########
$sql = "select count(*) as count from CustomerInfo where '$customerid' = CustomerID";
$result = mysqli_query($con,$sql)
or  die('Error: ' . mysql_error());

$row = mysqli_fetch_assoc($result);
    if ( $row['count']==0 ){
    "INSERT INTO CustomerInfo ('CustomerID') VALUES ('$customerid');";
    echo "<p>Customer ID Not Found. <br />New CustomerID Created.</p>";
   }

$sql2 = "select count(*) as count from EmployeeInfo where '$salespersonid' =  SalesPersonID;";
$result2 = mysqli_query($con,$sql)
 or  die('Error: ' . mysql_error());
 $row2 = mysqli_fetch_assoc($result2);

if ( $row2['count']==0 ){
"INSERT INTO EmployeeInfo ('SalesPersonID')VALUES ('$salespersonid');";
echo "<p>Salesperson ID Not Found. <br />New Salesperson ID Created.</p>";
}

    ########## FOREIGN KEY CHECK END ##########

    ########## DATA ENTRY SQL STATEMENT START ##########
$sql3 = "INSERT INTO Purchases (CustomerID, 
          PurchaseOrderNo, 
          PurchaseTotal, 
          DateOfPurchase, 
          SalesPersonID,
          SpecialOrder) 
VALUES ('$customerid',   
        '$purchaseorderno',
        '$purchasetotal',
        '$dateofpurchase',
        '$salespersonid',
        '$specialorder')";
    ########### DATA ENTRY SQL STATEMENT END ##########

    ########## INPUT SUCCESS/FAILURE REPORTING#########
if (mysqli_query($con, $sql3)) {
    echo "<P>Record Successfully Created</P><BR />";
} else {
  echo "Error: " . $sql9. "<br>" . mysqli_error($con);
}
mysqli_close($con);
echo "<P>Connection Successfully Closed.</P>";

Answer 1

You aren't executing your insert queries for CustomerInfo or EmployeeInfo

    $sql = "select count(*) as count from CustomerInfo where '$customerid' = CustomerID";
    $result = mysqli_query($con,$sql)
    or  die('Error: ' . mysql_error());

    $row = mysqli_fetch_assoc($result);
        if ( $row['count']==0 ){

    ###THE NEXT LINE DOESN'T DO ANYTHING###
        "INSERT INTO CustomerInfo ('CustomerID') VALUES ('$customerid');";
        echo "<p>Customer ID Not Found. <br />New CustomerID Created.</p>";
       }

Also you don't want to put single quotes around the column name in your insert statements so instead of:

INSERT INTO CustomerInfo ('CustomerID') VALUES ('$customerid')

you want:

INSERT INTO CustomerInfo (CustomerID) VALUES ('$customerid')