在PHP中将两个查询合并为一个

I need to make the following two queries into one but can't, When I try to test it it doesnt run at all and I'm not sure why. If anyone could help I would be thankful. This is my first query -

$exportArray[] = $row['reviewId'];
$row_num++;

$sql = <<<SQL
SELECT * FROM review WHERE (reviewForum = "$reviewForum") 

And this is my second -

$sql = "SELECT * FROM mom WHERE ( reviewId = " . $row['reviewId'] . " )";

I tried UNION but doesn't work either. The common fields between the two tables is reviewId. I am querying two tables and the first query above works but when I try to include the second one I can't get it to work. Thanks if anyone can help me, it's probably something small but I've been looking at it for a while now and it's very annoying at this stage.

You may try this:

SELECT a.*, b.*
FROM review a
JOIN mom b 
ON a.reviewId=b.reviewId
WHERE a.reviewForum ='$reviewForum'

I assume, reviewId is in both tables

SELECT m.*,r.* 
FROM review r
  LEFT JOIN mom m 
    ON r.reviewId = m.reviewId
WHERE r.reviewForum = "$reviewForum"