MyBatis-Plus Select Query Examples and Usage

The article introduces a series of MyBatis‑Plus tutorials titled “每天玩转3分钟 MyBatis‑Plus”, focusing on the select query functionality. After a brief recap of previous advanced query examples, it presents a new case study on using select queries.

Data preparation includes creating a user table and inserting sample records with fields such as id, name, age, email, manager_id, and create_time. The SQL statements are shown in a code block:

#创建用户表</code>
<code>CREATE TABLE user (</code>
<code>    id BIGINT(20) PRIMARY KEY NOT NULL COMMENT '主键',</code>
<code>    name VARCHAR(30) DEFAULT NULL COMMENT '姓名',</code>
<code>    age INT(11) DEFAULT NULL COMMENT '年龄',</code>
<code>    email VARCHAR(50) DEFAULT NULL COMMENT '邮箱',</code>
<code>    manager_id BIGINT(20) DEFAULT NULL COMMENT '直属上级id',</code>
<code>    create_time DATETIME DEFAULT NULL COMMENT '创建时间',</code>
<code>    CONSTRAINT manager_fk FOREIGN KEY (manager_id)</code>
<code>        REFERENCES user (id)</code>
<code>)  ENGINE=INNODB CHARSET=UTF8;</code>
<code>#初始化数据：</code>
<code>INSERT INTO user (id, name, age, email, manager_id, create_time)</code>
<code>VALUES (1087982257332887553, '大boss', 40, '[email protected]', NULL, '2019-01-11 14:20:20'),</code>
<code>    (1088248166370832385, '王天风', 25, '[email protected]', 1087982257332887553, '2019-02-05 11:12:22'),</code>
<code>    (1088250446457389058, '李艺伟', 28, '[email protected]', 1088248166370832385, '2019-02-14 08:31:16'),</code>
<code>    (1094590409767661570, '张雨琪', 31, '[email protected]', 1088248166370832385, '2019-01-14 09:15:15'),</code>
<code>    (1094592041087729666, '刘红雨', 32, '[email protected]', 1088248166370832385, '2019-01-14 09:48:16');

Case 1.1 – Query users aged 20, 21, 25, 26 and return only id and name (difficulty ★). The Java test method demonstrates using QueryWrapper with in and select:

/*</code>
<code> * 描述：例1.9 查询年龄为20、21、25、26的用户，且只返回id和name字段</code>
<code> * SQL语句：SELECT id,name FROM user WHERE age IN (20,21,25,26)</code>
<code> */</code>
<code>@Test</code>
<code>public void testSelectByQueryWrapper9() {</code>
<code>    System.out.println(("----- 查询年龄为20、21、25、26的用户，且只返回id和name字段 ------"));</code>
<code>    QueryWrapper<User> queryWrapper = new QueryWrapper<>();</code>
<code>    queryWrapper.in("age", Arrays.asList(20,21,25,26)).select("id","name");</code>
<code>    List<User> userList = userMapper.selectList(queryWrapper);</code>
<code>    userList.forEach(System.out::println);</code>
<code>}

Execution logs and result screenshots are included in the original article.

Case 1.2 – Query the same age set but return id , name , and manager_id (difficulty ★★). This example shows how to exclude unwanted columns using a lambda expression:

/*</code>
<code> * 描述：例1.10 查询年龄为20、21、25、26的用户，且只返回id、name、manager_id 字段</code>
<code> * SQL语句：SELECT id,name,manager_id FROM user WHERE age IN (20,21,25,26)</code>
<code> */</code>
<code>@Test</code>
<code>public void testSelectByQueryWrapper10() {</code>
<code>    System.out.println(("----- 查询年龄为20、21、25、26的用户，且只返回id、name、manager_id 字段 ------"));</code>
<code>    QueryWrapper<User> queryWrapper = new QueryWrapper<>();</code>
<code>    queryWrapper.in("age", Arrays.asList(20,21,25,26))</code>
<code>            .select(User.class, info -> !info.getColumn().equals("email") && !info.getColumn().equals("create_time"));</code>
<code>    List<User> userList = userMapper.selectList(queryWrapper);
<code>    userList.forEach(System.out::println);
<code>}

Logs and result images are also provided.

The article concludes with links to other parts of the “每天玩转3分钟 MyBatis‑Plus” series and a call‑to‑action to follow the “悟空聊架构” public account for more resources.