Checking mysql insertion query

Question

I wrote a query but now I'm having doubts.

The first one I have to insert a CD supplied by a particular supplier and produced by a particular producer.

$sql="INSERT INTO cd (supplier_name, 
                      supplier_address, 
                      producer_name, 
                      producer_address, 
                      cd_title, 
                      cd_type, 
                      cd_year) 
             VALUES ('$_POST[supp_name]', 
                     '$_POST[supp_addr]', 
                     '$_POST[prod_name]', 
                     '$_POST[prod_addr]', 
                     '$_POST[cd_title]', 
                     '$_POST[cd_year]' , 
                     '$_POST[cd_type]')";

But then I realized, I have a table called CD with ONLY THREE ATTRIBUTES, title, year and type. CD(title, year, type). However, how I just need to insert the CD information by a particular supplier X and particular producer Y. How do I do that?

Also, my form for data entry looks like this:

<form action="cd.php" method="post">
<h4> Enter CD information </h4> 
CD Title: <input type="text" name="cd_title"><br>
CD Year: <input type="text" name="cd_year"><br>
CD Type: <input type="text" name="cd_type"><br>

<h4>Enter supplier information</h4>
Supplier Name:  <input type="text" name="supp_name"><br>
Supplier Address:<input type="text" name="supp_addr"><br>


<h4> Enter producer information </h4> 
Producer Name:<input type="text" name="prod_name"><br>
roducer Address:<input type="text" name="prod_addr"><br>

<input type="submit" name="submit" value="Submit">

So, I'm wondering if a user enters the above data, where does it get stored? Under what table? (That is, where does the supplier and producer info get stored?

Answer 1

I'm not sure exactly how you mean, but I'll give it a try:

Try using a select with joins to Supplier and Producer table:

SELECT * FROM CD
JOIN Supplier S ON CD.Supplied = S.Supplied
JOIN Producer P ON CD.Produced = P.Produced
WHERE S.name = X AND P.name = Y

If above query returns true, then do the insert.

UPDATE: Now when looking at your html-form I think I understand what you're looking for...

You want a relationsship between CD-table and Producer-table AND a relationsship between CD-table and Supplier-table.

You do this relation by adding and supplier_id-column in your CD-table and a producer_id**-column in your CD-table

AND

an autoincremental id in both Supplier-table and in the Producer-table.

The last step with the actual db is to to create constraints between supplier_id and id-column of supplier-table and producer_id and id-column of producer-table.

When you've done that, you might do something like this:

//When form is submitted...


//First query  (Insert this only if it doesn't already exist in Supplier-table - IGNORE keyword takes care of this)
$sql1="INSERT IGNORE INTO Supplier (supplier_name, 
                      supplier_address) 
             VALUES ('$_POST[supp_name]', 
                     '$_POST[supp_addr]', 
                     )";

//Execute query $sql1
//Get last inserted id from query $sql1 and store it in $idLastInsertedSupplier


//Second query  (Insert this only if it doesn't already exist in Producer-table - IGNORE keyword takes care of this) 
$sql2="INSERT IGNORE INTO Producer (producer_name, 
                      producer_address) 
             VALUES ('$_POST[prod_name]', 
                     '$_POST[prod_addr]')";

//Execute query $sql2
//Get last inserted id from query $sql2 and store it in $idLastInsertedProducer

//Insert CD-table query: 
    $sql="INSERT INTO CD (
                          cd_title, 
                          cd_type, 
                          cd_year,
                          supplier_id,
                          producer_id
                          ) 
   VALUES ('$_POST[cd_title]', 
                         '$_POST[cd_year]' , 
                         '$_POST[cd_type]',
$idLastInsertedSupplier,$idLastInsertedProducer)";

Of course you should use prepared statements (with placeholders) with PDO or Mysqli. I have not taken security of SQL into account (not using placeholder, not sanitizing data etc).

Why id's? You could insert into all values into all three tables without having references (ids) between the tables, but then there would be no point of having a relational database. It would also be much harder to do all SQL-operations afterward. Let's say you would want a list of all cd's with their producers and suppliers.

With relational storage (with their id's) you could execute an sql-statement like this:

SELECT * FROM CD
JOIN Supplier S ON CD.id = S.id
JOIN Producer P ON CD.id = P.id

and just fetch the rows.

There is no good way of doing the same thing without having these references. (It's impossible for the db to know which row in producer-table that belongs to which row in the CD-table without having any reference). You COULD of course add name of producers and suppliers in the CD-table also, but then there would be duplicates and for the most of the time you don't want that (in some extreme cases for speed it would be the only option to have these duplicates though).

I hope I made it clearer now.