var_storage:
id | var_name | var_value | user


post:
id | user

post_var_storage:
post_id | var_storage_id

SELECT * FROM
post p
WHERE

    # MEAL=DINNER
    EXISTS (
        SELECT * FROM (
            SELECT *
            FROM post p2
            INNER JOIN post_var_storage pvs ON pvs.post_id = p2.id
            INNER JOIN vars_storage vs ON pvs.var_storage_id = vs.id
            WHERE p2.id = p.id
        ) vs
        WHERE
            vs.var_name = "MEAL" AND vs.value = "DINNER"
    ) AND

    # FOOD=FRIES
    EXISTS (
        SELECT * FROM (
            SELECT *
            FROM post p2
            INNER JOIN post_var_storage pvs ON pvs.post_id = p2.id
            INNER JOIN vars_storage vs ON pvs.var_storage_id = vs.id
            WHERE p2.id = p.id
        ) vs
        WHERE
            vs.var_name = "FOOD" AND vs.value = "FRIED"
    ) AND

    ....