wpdb query gives back a wrong result

I’ve written some code in my PHP snippet which is on my WordPress page and the wpdb query gives me always a wrong result.

In WordPress

$column07a = $_POST[$attributes[8]];         **<-** echo displayed **24253**

$queryColumn07 = $wpdb->prepare( " SELECT DISTINCT p.id 
                        FROM plz p 
                            LEFT JOIN vermieter v ON v.id_plz=p.id 
                        WHERE p.postleitzahl='$column07a' " );`     

$column07 = $wpdb->query( $queryColumn07 ); **<-** echo displayed **1** 

In SQL

SELECT DISTINCT p.id 
FROM plz p 
    LEFT JOIN vermieter v ON v.id_plz=p.id 
WHERE p.postleitzahl='24253';   

phpmyadmin displayed 3 which is the correct result for that query

What did I do wrong? May you help me in someway?

Answer

The reason why you’re getting 1 as a result is because you’re using the query() method instead of get_results() or get_var().

From the $wpdb::query() documentation:

Return:

(int|bool) Boolean true for CREATE, ALTER, TRUNCATE and DROP queries. Number of rows affected/selected for all other queries. Boolean false on error.

(Emphasis mine.)

So, when you run this:

$column07 = $wpdb->query( $queryColumn07 );

You get 1 because query() is returning the number of rows found by your SELECT query.

In your specific case, as pointed out earlier, you want to use get_var() instead to get the actual ID returned by the query:

$column07 = $wpdb->get_var( $queryColumn07 );

echo $column07; // Should output 3 according to your comments.