Specify field query in using mybatis

1: Requirement: query the student numbers and names of students who have studied all the courses taught by teacher "Ye Ping";

1 List<Map<String,Object>> selectYepingAllCourse(@Param("name") String name);

use

List<Map<String,Object>> to receive the data queried from the database

1 <!--Student number and name of all the students taught by Mr. Yeping-->
 2 <select id="selectYepingAllCourse" resultMap="Base_ResultMap">
 3              SELECT
 4              a.s_id,
 5              a.sname
 6          FROM
 7              a_student a
 8          WHERE
 9              a.s_id IN (
 10                  SELECT
 11              a.s_id
 12          FROM
 13              a_sc a
 14          INNER JOIN a_course b ON a.c_id = b.c_id
 15          INNER JOIN a_teacher c ON c.t_id = b.t_id
16         WHERE
17             c.tname = #{name}
18         GROUP BY
19             a.s_id
20         HAVING
21             count(a.c_id) = (
22                 SELECT
23                     count(a_course.c_id)
24                 FROM
25                     a_course
26                 INNER JOIN a_teacher ON a_teacher.t_id = a_course.t_id
27                 WHERE
28                     a_teacher.tname = #{name}
29             )
30             );
31 </select>

Analyze this sql.

1 : Which students have studied Teacher Ye Ping's class?
    SELECT
    a.s_id,count(a.c_id)
    FROM
    a_sc a
    INNER JOIN a_course b ON a.c_id = b.c_id
    INNER JOIN a_teacher c ON c.t_id = b.t_id
            WHERE
    c.tname = 'Yeping'
    GROUP BY
    a.s_id
    2 : Mr. Ye Ping taught several classes.
    SELECT
            count(a_course.c_id)
        FROM
            a_course
        INNER JOIN a_teacher ON a_teacher.t_id = a_course.t_id
        WHERE
            a_teacher.tname = 'Yeping'
    )
    3 : Learn the information of the students who have the same class as Mr. Ye Ping's class.
    SELECT
    a.s_id
FROM
    a_sc a
INNER JOIN a_course b ON a.c_id = b.c_id
INNER JOIN a_teacher c ON c.t_id = b.t_id
WHERE
    c.tname = 'Yeping'
GROUP BY
    a.s_id
HAVING
    count(a.c_id) = (
        SELECT
            count(a_course.c_id)
        FROM
            a_course
        INNER JOIN a_teacher ON a_teacher.t_id = a_course.t_id
        WHERE
            a_teacher.tname = 'Yeping' 
    )

test:

/**
     * Query the student numbers and names of students who have studied all the courses taught by teacher "Ye Ping";
     */
    @Test
    public void testSelectYepingAllCourse(){
        List<Map<String, Object>> list = ascMapper.selectYepingAllCourse("李一");
        for (Map<String,Object> i:list){
            System.out.println(i);
        }
    }

The result of the output:

Get the value of the Map collection in the List collection.

1  for ( int i=0;i<list.size();i++ ){
 2              Map map= list.get(i);
 3              // It is received by set. cannot be repeated. No order 
4              Set set = map.keySet();
 5              System.out.println("set value" + set);
 6              Object sId = map.get("sId" );
 7              System.out.println("Get sId value "+ sId);
 8          }

Output result: This one has only one result.

See below for several results.

Specify field query in using mybatis

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