使用新值更新联结表

Question

I have a one-to-many table (actually application will actually use a many-to-many, but that is not relevant to my question). Assume two columns with the following values:

c1 c2
 2  3
 4  1
 4  3
 4  4
 6  4

For a given c1 value of 4, I would like to update the table with the c2 values in array [1,2,4,6]. As such, my table will now be as follows (note that records 4,2 and 4,6 were added, record 4,3 is no longer present, and records 4,1 and 4,4 remain unchanged):

c1 c2
 2  3
 4  1
 4  2
 4  4
 4  6
 6  4

What is the best way to accomplish this? I "could" first query the database to select the existing values for c1=4, and then use array_intersect() to identifiy the added and removed records, and insert/delete as required, however, this seems excessive.

Answer 1

I know this is old, but it took me a while to find the answer and this question ranks high on google.

I found the following code and modified it:

INSERT IGNORE INTO my_table VALUES (1,1), (1,2), (1,3);

DELETE FROM my_table WHERE c1 NOT IN (1,2,3) AND my_table = 1;

Origin of source code: http://borzacchiello.it/how-to-update-a-junction-table/

My code that I modified to use with PHP variables & PDO loops:

    $a_id = $my_main_id //this would be c1 in the above question

    //Set Variable From Post
    $var_1 = isset($_POST['var_1']) ? $_POST['var_1'] : '';
    $var_2 = isset($_POST['var_2']) ? $_POST['var_2'] : '';
    //etc, etc, etc

    //put variables into array
    $data = array('var_1'=>$var_1, 'var_2'=>$var_2, 'var_3'=>$var_3, 'var_4'=>$var_4, 'tarp_5'=>$tarp_5);

                       //get count of variable that contain data and not empty
                       $data_array_count = 0;
                       foreach ($data as $column => $value) {     
                                if($value != '') {
                                    $data_array_count = ++$data_array_count;
                                }
                       }

                       //if contains atleast one variable run update code     
                       if($data_array_count != 0) {

                            //loops through and inserts each varible in array
                            foreach ($data as $column => $value) {

                                //ignores variables without any data
                                if($value != '') {  
                                    $insert = $db->prepare("INSERT IGNORE my_table (a_id, b_id) VALUES (:a_id, :b_id)"); 
                                    $insert->execute(array(':a_id' => $a_id,
                                                           ':b_id' => $value ));        
                                }
                            }


                                //sets up variables in array to remove any records that need to be deleted
                                $columns = "";  
                                $holders = "";  
                                foreach ($data as $column => $value) {     
                                    if($value != '') {      
                                       $columns .= ($columns == "") ? "" : ", ";  
                                       $columns .= $column;  
                                       $holders .= ($holders == "") ? "" : ", ";  
                                       $holders .= ":$column";  
                                    }
                                }


                                $delete = $db->prepare("DELETE FROM my_table WHERE accessory_id NOT IN ($holders) AND (carrier_id = :a_id)"); 

                            //bind value for main id     
                            $delete->bindValue(":a_id", $a_id);

                            //loop to bind value for each variable stored in array with data
                            foreach($data as $placeholder => $value) {
                                if($value != '') {
                               $delete->bindValue(":" . $placeholder, $value);
                                }
                            }

                            $delete->execute();      

                    } 

Using the example from the original question you would have to run this code for each c1 id number that you wanted to update ( c1 would be the equivalent of the $a_id variable in my example).