Hello,

when I run same query with different indexes (USE INDEX to force another index), I get completely different results. I discovered this issue after upgrade to version 10.11, some queries started to return nonsense. Does work correctly in <10.11.

This fiddle shows the code but does not exhibit the problem (version 10.9 is not affected) - https://dbfiddle.uk/eJwzXdgt both queries returns the same value. But when I run this in 10.11 or 11.1, first query returns all NULLs (invalid result), second query returns valid results.

Queries differ only in index used.

SELECT 

    (

    SELECT

        SUM(ps3.quantity)

    FROM

        products_stores ps3 USE INDEX (products_stores_id_store_id_product_id_variation_uindex)

    WHERE

        ps3.id_product = p.id AND ps3.id_variation <=> ps.id_variation AND ps3.id_store = 1

) AS store3_quantity

FROM

    products_stores ps

LEFT JOIN products p ON

    p.id = ps.id_product;