a b c三表联合查询问题

问：

SELECT
            a.channel,
            b.type proOperateType,
            c.type catOperateType,
            a.shop_code shopCode,
            a.status syncStatus,
            a.type errorType,
            a.name,
            a.code,
            a.reason
        FROM fresh_menu_error_msg a
        LEFT JOIN fresh_product_sync b on a.request_id = b.request_id
        LEFT JOIN fresh_category_sync c on a.request_id = c.request_id
        where a.company_id = '2399'
        order by a.create_date desc

大佬 这个sql a b c三张表关联，，但是一个关联条件requestId只能同时存在 a b ，或者 a c两张表里，，这里用inner join查出来的100%是空的，，所以还有什么别的优化方法么？

答：

SELECT  a.*,b.`type` FROM fresh_menu_error_msg a
INNER JOIN fresh_product_sync b ON a.request_id = b.request_id 
WHERE a.`company_id` = '2399'
UNION ALL
SELECT a.*,c.`type` FROM fresh_menu_error_msg a
INNER JOIN fresh_category_sync c ON a.request_id = c.request_id
WHERE a.`company_id` = '2399'

哦 忘了 a.company_id， b.request_id ，c.request_id 都加个索引