Question

I have the following code:

    $sql = "SELECT table.field, table2.field2 FROM
                table, table2";
    $stmt = $this->db->prepare($sql);
    $stmt->execute();

    $x = $stmt->fetchAll(PDO::FETCH_ASSOC);

I know it is not enough information, but I do not understand why the code executes only if I comment the fetchAll line. When that line executes, I do not get anything, just blank browser, no errors or anything. In firebug the response is blank… What can it be??

Answer 1

You are doing a Cartesian product of table and table2. This can be a HUGE amount of data.

For each row in table, you are getting all the rows in table2. So if table has 100 lines, and table2 has 500 lines, your query will try to fetch 50.000 lines.

You’ll either want a JOIN:

SELECT table.field, table2.field2 
FROM table 
JOIN table2 
ON table.field3 = table2.field3

Or a UNION

SELECT table.field AS FIELDNAME FROM table
UNION ALL
SELECT table2.field2 AS FIELDNAME FROM table2

If a Cartesian product is really what you want, try adding a LIMIT and see if that works. Then later increase or remove the limit

SELECT table.field, table2.field2 
FROM table, table2 LIMIT 10

Depending on what your tables contain (you indeed did not give enough info).