select a.* ,b.flow_id from daiban_order_serve as a left join daiban_order_serve_flow as b on b.daiban_serve_id = a.id where 1 and supplier_id = 23 and b.uid = 100031 and b.is_kais = 2 and b.is_accept = 1 order by create_time desc limit 0,20 帮我优化一下这个mysql语句去除重复daiban_serve_id值的，但是要优先显示is_kais不等于2的

好的，这个 mysql 语句可以这样优化：

SELECT DISTINCT a.*, b.flow_id
FROM daiban_order_serve AS a
LEFT JOIN (
SELECT daiban_serve_id, MAX(flow_id) flow_id
FROM daiban_order_serve_flow
WHERE uid = 100031 AND is_accept = 1
GROUP BY daiban_serve_id
) AS b
ON b.daiban_serve_id = a.id
WHERE supplier_id = 23 AND IFNULL(b.is_kais != 2, true)
ORDER BY create_time DESC
LIMIT 0, 20;

这个语句会对 daiban_order_serve 和 daiban_order_serve_flow 两张表进行左联接，然后使用子查询获取每个 daiban_serve_id 对应的最大流程 ID 和去重后的结果集。

注意我用了 IFNULL(b.is_kais != 2, true) 来判断 is_kais 不等于 2，这样既可以显示 is_kais 不等于 2 的记录，也可以显示没有记录的 daiban_order_serve。