对于这种简单的情况,通常来说,使用IN的查询性能会稍微优于JOIN。 JOIN涉及多表的连接操作,而IN只是简单地过滤出指定条件的数据。在某些情况下,数据库优化器可能会将IN子查询转换为JOIN,但这仍然取决于具体的查询和表结构。 何时使用JOIN 虽然上述简单的性能对比显示IN可能稍微快一些,但在实际应用中,JOIN通常更具灵活...
$mysqli = new mysqli('127.0.0.1', 'root', 'root', 'test');if ($mysqli->connect_error) { die('Connect Error (' . $mysqli->connect_errno . ') ' . $mysqli->connect_error);}$result = $mysqli->query('select order.id, price, user.`name` from `order` join user on ...
$result = $mysqli->query('select order.id, price, user.`name` from `order` join user on order.user_id = user.id;');$orders = $result->fetch_all(MYSQLI_ASSOC);var_dump($orders);$mysqli->close(); 下面是 in 查询的执行脚本: $mysqli = new mysqli('127.0.0.1', 'root', '...
k , i I would only like to get a set of unique pairs that is a b g h i k I tried joins and selecting distinct but I get twice the set or just a subset Any suggestions very much appreciated. Subject Written By Posted Distinct and join query in MySQL ...
in 复制 $mysqli = new mysqli('127.0.0.1', 'root', 'root', 'test'); if ($mysqli->connect_error) { die('Connect Error (' . $mysqli->connect_errno . ') ' . $mysqli->connect_error); } $result = $mysqli->query('select `id`,price,user_id from `order`'); ...
1 row in set (0.00 sec) 这里的显示和通过紧凑索引扫描实现 GROUP BY 也完全一样。实际上,这个 Query 的实现过程中,MySQL 会让存储引擎扫描 group_id = 2 的所有索引键,得出所有的 user_id, 然后利用索引的已排序特性,每更换一个 user_id 的索引键值的时候保留一条信息,即可在扫描完所有 gruop_id = ...
1)在关联查询的时候，尽量在被驱动表的关联字段上加索引，让MySQL做join操作时尽量选择INLJ算法。2）小...
今天在查询mysql表连接的时候发现一篇对join深度解析的文章感觉很不错,讲解的很到位,放在这里给大家分享一下。 join简介 多表联合查询,有内连接,外连接,右连接,左连接,自然连接。 笛卡尔积CROSS JOIN 笛卡尔积就是将A表的每一条记录与B表的每一条记录强行拼在一起。所以,如果A表有n条记录,B表有m条记录,笛卡...
Query OK, 2 rows affected (0.02 sec) mysql> insert into test2 (a,d,e) values(1,3,"test2_record1"),(2,3,"test2_record2"); Query OK, 2 rows affected (0.02 sec) mysql> select * from test1 join test2 on test1.b=test2.d; ...
IN查询语句:SELECT CONCAT(first_name,last_name) FROM customer WHERE customer_id IN (SELECT customer_id FROM rental WHERE rental_id <=16000); 结果(返回了599条客户名字信息): 慢查询日志: #Time:16071721:17:58#User@Host: root[root] @ localhost [127.0.0.1] Id:17# Query_time:0.000000Lock_time...