php mysqli fetch_assoc忽略左连接的空值

Question

I have a problem and don't know why my mysqli query does not work correctly in PHP.

I have two tables:

table 1 "reviews"
id | dateCreated | reviewText | ...

table 2 "issues"
id | reviews_id | issueText | ...

Table 1 contains reviews from users. Table 2 contains issues (complaints) for certain reviews. However one review does not necesarrily need to have a issue (if nobody reported it). The query is:

SELECT reviews.*, issues.* 
FROM reviews 
LEFT JOIN issues 
    ON reviews.id=issues.reviews_id 
WHERE (reviews.idVenue='6438' OR reviews.idVenue='6444' OR reviews.idVenue='7590' ) 
ORDER BY 'reviews.updated' DESC 

This works perfectly if one issue exists for a review (ON clause is true).

However if there is no issue existing for the review (the ON clause is not true), then reviews.id and issues.reviews_id are missing in the $row that was fetched with

if($result = $this -> mysqli -> query($qstr)){
    while($row = $result->fetch_assoc()){
        $temp[] = $row;
        }
}

Also all the other colums from issues are missing in $row because they are NULL. With missing I mean, that they are not there if I print $row or check $row as a watch variable in the netbeans debugger. It just doesn't show reviews.id and issues.reviews_id.

If I run the query above directly in phpmyadmin, then it returns all columns correctly with the value NULL for the cases where no related issue was found for a review.

So my question is, why does PHP ignore the NULL values and does not return them in $row but phpmyadmin does?

Thanks!

Answer 1

Here's my comment in more descriptive information in case someone runs into this in the future.

When you call fetch_assoc php assign columns names as keys & their values as the values of the array, As the keys of an array are unique any entry that holds the same id will be overwritten.

In your example both reviews & issues have a column named 'id' therefore you'll always get the value from the last 'id' column you used in your select statement.

An easy fix for this (without having to permanently change your columns names) is to use aliases in your query. eg: SELECT reviews.*, issues.id as `issue_id`, issues.issueText