Problems while trying to make a query using left join and group by with having over a field of the left table on MySQL

Im trying to make some queries, first, I do this one (and works):

SELECT RP.id, RP.product_name, RP.price, RP.retailer_id, RP.product_id, 
count(G.id) AS duration, G.active, RP.retprod_id, P.pr_id AS video 
FROM retailer_products AS RP 
LEFT JOIN groups G ON RP.id=G.retailer_product_id 
INNER JOIN products P ON P.id=RP.product_id 
WHERE (RP.product_id IN (1)) 
GROUP BY RP.id;

But when I do this one, it gaves me an empty set, the difference is that it has a "HAVING" at the end of the query over a field that may be: 0, 1 or NULL (because of the LEFT JOIN, I have no groups linked to the table retailer_product)

SELECT RP.id, RP.product_name, RP.price, RP.retailer_id, RP.product_id, 
count(G.id) AS duration, G.active, RP.retprod_id, P.pr_id AS video 
FROM retailer_products AS RP 
LEFT JOIN groups G ON RP.id=G.retailer_product_id 
INNER JOIN products P ON P.id=RP.product_id 
WHERE (RP.product_id IN (1)) 
GROUP BY RP.id HAVING G.active=1;

So, I tried the following ways but no one works:

-- HAVING G.active=1

-- HAVING G.active=1 开发者_Go百科OR G.active=NULL

-- HAVING G.active0

What is the right way to handle this on MySQL? Thanks in advance!

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The proper way to compare value with NULL is IS NULL. So you need to add HAVING G.active IS NULL OR G.active=1. Your code G.active=NULL is always NULL (false):

1 = NULL // NULL - false in conditions
NULL = NULL // NULL - false in conditions
NULL IS NULL // TRUE

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Why you don't add the HAVING condition on the "Group" ON condition?

SELECT RP.id, RP.product_name, RP.price, RP.retailer_id, RP.product_id, 
count(G.id) AS duration, G.active, RP.retprod_id, P.pr_id AS video 
FROM retailer_products AS RP 
LEFT JOIN groups G ON RP.id=G.retailer_product_id AND G.active=1
INNER JOIN products P ON P.id=RP.product_id 
WHERE (RP.product_id IN (1)) 
GROUP BY RP.id;