PHP MySQL optimal way to perform multiple dependent queries

Question

I need to query (read) some data, and analyze it before performing another query (read) on a different table.

I've looked at mysqli multiple statements but they don't have documentation for situations where the second query depends on the result of the first query.

It seems my current code of doing two queries might not be optimal. Is there a more optimal way to do this?

//FIRST QUERY
$query1= "SELECT color FROM products WHERE type = '$productType';";
$result = $conn->query($query1);

if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        $colorProduct = $row["color"];
    }
} 


//ANALYZE SEARCH RESULT FROM FIRST QUERY
if ($colorProduct == "green") {
    $colorType = "greenColorType";
}   
//a lot more analysis


//SECOND QUERY
$query2 = "SELECT price FROM Vendors WHERE color = '$colorType';";
$result2 = $conn->query($query2);

if ($result2->num_rows > 0) {
    while($row = $result2->fetch_assoc()) {
        $priceOfProduct = priceOfProduct . $row["price"];
    }
} 

$conn->close();

Thank you in advance.

Answer 1

Why don't you join those 2 queries into one and analyse later if you need to. For example:

"SELECT price FROM products
JOIN Vendors ON Vendors.color = products.color
WHERE type = $productType
AND color = 'green';"

MySQL is declarative language so it is usually better to "tell it" what you want and than modify data afterwards (if needed).

Answer 2

First, you have to add a "and" to the "where" clause : SELECT color FROM products WHERE type = '$productType' and color = 'green'

Then you have to join or to add a sub query in SQL.

In fact, you should do only one SQL request.

Answer 3

Looks like your color values in the vendors table all have ColorType added after the actual colour name, which you are dealing with in PHP, before making a second query.

Mysql can do this for you. Here's an example:

"SELECT a.color, b.price FROM products a, vendors b WHERE a.type = '$productType' AND a.color = SUBSTR(b.color,1,LENGTH(a.color);"

The WHERE clause specifies a match on your $productType variable with the type column of table a (products) and a match between the color value in table a and the beginning of the color value in table b. It uses the LENGTH statement to match regardless of the length of the color in table a. So if color in table a is darkblue and table b is darkblueColorType it will match, and if the values are red and redColorType it will still match.