MySQL 如何针对单个表优化多个SELECT语句

为了优化多个SELECT语句，只需使用一次并将IN()应用于抓取多个值。 首先让我们创建一个表 –

mysql> create table DemoTable
(
    Id int,
    Name varchar(100),
    Age int
);
Query OK, 0 rows affected (0.77 sec)

使用insert命令将一些记录插入表中 –

mysql> insert into DemoTable values(1,'Chris',23);
Query OK, 1 row affected (0.39 sec)
mysql> insert into DemoTable values(2,'David',21);
Query OK, 1 row affected (0.56 sec)
mysql> insert into DemoTable values(3,'Mike',24);
Query OK, 1 row affected (0.28 sec)
mysql> insert into DemoTable values(4,'Robert',22);
Query OK, 1 row affected (0.12 sec)

使用select语句显示表中的所有记录 –

mysql> select *from DemoTable ;

这将产生以下输出 –

+------+--------+------+
| Id   | Name   | Age  |
+------+--------+------+
|    1 | Chris  |   23 |
|    2 | David  |   21 |
|    3 | Mike   |   24 |
|    4 | Robert |   22 |
+------+--------+------+
4 rows in set (0.00 sec)

以下是针对单个表优化多个SELECT语句的查询 –

mysql> select Name from DemoTable where Age in(21,22,23);

这将产生以下输出 –

+--------+
| Name   |
+--------+
| Chris  |
| David  |
| Robert |
+--------+
3 rows in set (0.00 sec)

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