好资源导航 » 文章资讯 » MySQL查询有效选择多行？

MySQL查询有效选择多行？

2024-04-24 03:30:27 378

您需要使用索引来有效地选择多行。让我们首先创建一个表-

mysql> create table DemoTable1501
   -> (
   -> Id int NOT NULL PRIMARY KEY,
   -> URL text
   -> );

这是创建索引的查询-

mysql> create index id_index on DemoTable1501(Id);
Records: 0  Duplicates: 0  Warnings: 0

使用插入命令在表中插入一些记录-

mysql> insert into DemoTable1501 values(101,'www.facebook.com');
mysql> insert into DemoTable1501 values(110,'www.google.com');
mysql> insert into DemoTable1501 values(220,'www.gmail.com');
mysql> insert into DemoTable1501 values(350,'www.youtube.com');

使用select语句显示表中的所有记录-

mysql> select * from DemoTable1501;

这将产生以下输出-

+-----+------------------+
| Id  | URL              |
+-----+------------------+
| 101 | www.facebook.com |
| 110 | www.google.com   |
| 220 | www.gmail.com    |
| 350 | www.youtube.com  |
+-----+------------------+
4 rows in set (0.00 sec)

以下是查询以有效地选择多行-

mysql> select * from DemoTable1501
   -> where Id in(101,220,350);

这将产生以下输出-

+-----+------------------+
| Id  | URL             |
+-----+------------------+
| 101 | www.facebook.com |
| 220 | www.gmail.com    |
| 350 | www.youtube.com  |
+-----+------------------+
3 rows in set (0.00 sec)

为了证明这一点，请使用SHOW命令，其中Handler_read_key使用4个ID中的3个-

mysql> SHOW STATUS LIKE 'Handler_%';

这将产生以下输出-

+----------------------------+-------+
| Variable_name              | Value |
+----------------------------+-------+
| Handler_commit             |     1 |
| Handler_delete             |     0 |
| Handler_discover           |     0 |
| Handler_external_lock      |     2 |
| Handler_mrr_init           |     0 |
| Handler_prepare            |     0 |
| Handler_read_first         |     0 |
| Handler_read_key           |     3 |
| Handler_read_last          |     0 |
| Handler_read_next          |     0 |
| Handler_read_prev          |     0 |
| Handler_read_rnd           |     0 |
| Handler_read_rnd_next      |     0 |
| Handler_rollback           |     0 |
| Handler_savepoint          |     0 |
| Handler_savepoint_rollback |     0 |
| Handler_update             |     0 |
| Handler_write              |     0 |
+----------------------------+-------+
18 rows in set (0.00 sec)

返回顶部
3162201930
czq8825@qq.com

MySQL查询有效选择多行？

热门推荐

随机推荐