为什么这个SQL查询在外连接上失败？

Question

我正在尝试运行以下查询：

        SELECT tmp1.post_parent, external_qty, internal_qty
        FROM (
            SELECT wp_posts.post_parent, SUM(wp_shoesol_inventory.qty) as external_qty
            FROM wp_posts
            INNER JOIN wp_variation_sku ON (wp_posts.ID = wp_variation_sku.variation_id)
            INNER JOIN wp_shoesol_inventory ON (wp_shoesol_inventory.sku = wp_variation_sku.sku )
            GROUP BY wp_posts.post_parent
        ) as tmp1
        FULL OUTER JOIN (
            SELECT wp_posts.post_parent, SUM(wp_storage_manager.product_quantity) as internal_qty
            FROM wp_posts
            INNER JOIN wp_variation_sku ON (wp_posts.ID = wp_variation_sku.variation_id)
            INNER JOIN wp_storage_manager ON (wp_storage_manager.variation_id = wp_variation_sku.sku )
            GROUP BY wp_posts.post_parent
        ) as tmp2 ON tmp1.post_parent = tmp2.post_parent 

但它失败并显示以下消息：

  

您的SQL语法有错误;查看与您的MySQL服务器版本对应的手册，以便在'FULL OUTER JOIN附近使用正确的语法（               SELECT wp_posts.post_parent，SUM（第9行的wp_storage_manager.product'

感谢所有帮助者！