MYSQL插入多个表

Question

我有4个表，第一个表有主键，另外3个表有第一个表中的外键。我的问题是，我可以插入其他3个表但我不能插入第一个表。其他3个表的外键empID没有值，它是第一个表的主键。

这是我的插入部分中的代码

    //INSERT--------------------------------------------------      
//PERSONAL INSERT-------------------------------------------    
    $sql = "INSERT INTO personal(empID,lastName,firstName,midInit)
        VALUES('$empID','$lastName','$firstName','$midInit')";

//EMPLOYMENT INSERT-------------------------------------------
    $sql2 = "INSERT INTO emp_econprof(empID,empStat,offDes,workNature,hrsPerweek)
        VALUES('$empID','$empStat','$offDes','$workNature','$hrsPerWeek')";
//LIVING INSERT----------------------------------------------
    $sql3 = "INSERT INTO living_enviprof(empID,houseNo,street,barangay,
                    munCity)
                VALUES('$empID','$houseNo','$street','$barangay','$munCity')";
//FAMILY INSERT-----------------------------------------------
    $sql4 = "INSERT INTO family_prof(empID,spouseLname,spouseFname,spousemidInit,
                         spouseLiving,ocwSpouse,tot_childNo,diedChild,aliveChild)
                VALUES('$empID','$spouseLname','$spouseFname','$spousemidInit',
                         '$spouseLiving','$ocwSpouse','$tot_childNo',
                          '$diedChild','$aliveChild')";

            $db->exec($sql);
            $db->exec($sql2);
            $db->exec($sql3);
            $db->exec($sql4);

我的代码中缺少什么？