Question

SELECT * FROM
    (SELECT * FROM customer ORDER BY customer_id ASC  LIMIT 1 )DUMMY_ALIAS1
UNION ALL 
SELECT * FROM
    ( SELECT * FROM customer  ORDER BY customer_id DESC LIMIT 1)DUMMY_ALIAS11

获取最后和第一条记录的其他替代方法是什么，我认为我的查询未经过优化

Answer 1

您的查询很好，没有任何问题，但您可以稍微简化一下：

(SELECT * FROM customer ORDER BY customer_id ASC LIMIT 1)
UNION ALL
(SELECT * FROM customer  ORDER BY customer_id DESC LIMIT 1)

没有必要使用外部查询和别名，但不要忘记在customer_id上添加索引：

alter table customer add index idx_customer_id (customer_id);

或（可能更好，但这取决于上下文）将其定义为主键：

alter table customer add primary key (customer_id);

这将使您的查询得到优化。

Answer 2

试试这个：

SELECT c.* 
FROM customer c
INNER JOIN ( SELECT MIN(customer_id) AS minCustomerId, 
                    MAX(customer_id) AS maxCustomerId 
             FROM customer
           ) AS b ON c.customer_id IN (minCustomerId, maxCustomerId);

从数据库表中获取最后一条和第一条记录的替代方法

2 个答案: