可以MySQL嵌套选择返回结果列表

Question

我想编写一个mysql语句,它将返回一个表中的结果列表以及另一个表中逗号分隔的字段列表.我想一个例子可能更好地解释它

Table 1
========================

id First_Name Surname
----------------------
1  Joe       Bloggs
2  Mike      Smith
3  Jane      Doe

Table 2
========================

id Person_Id Job_id
---------------------
1  1         1
2  1         2
3  2         2
4  3         3
5  3         4

我想返回一个逗号分隔的job_id列表的人员列表.所以我的结果集将是

id First_Name Surname job_id
------------------------------
1  Joe       Bloggs   1,2
2  Mike      Smith    2
3  Jane      Doe      3,4

我猜sql会是这样的

select id, First_Name, Surname, (SELECT job_id FROM Table 2) as job_id from Table 1

但显然这不起作用,因此需要将'(SELECT job_id FROM Table 2)更改为job_id'部分.

希望这是有道理的

谢谢约翰

Answer 1

您可能想要使用该GROUP_CONCAT()功能,如下所示:

SELECT    t1.id, 
          t1.first_name, 
          t1.last_name,
          GROUP_CONCAT(DISTINCT job_id ORDER BY job_id SEPARATOR ',') job_id
FROM      Table1 t1
JOIN      Table2 t2 ON (t2.Person_id = t1.id)
GROUP BY  t1.id;

让我们用你的示例数据测试它:

CREATE TABLE Table1 (
    id int AUTO_INCREMENT PRIMARY KEY, 
    first_name varchar(50), 
    last_name varchar(50));

CREATE TABLE Table2 (
    id int AUTO_INCREMENT PRIMARY KEY, 
    person_id int,
    job_id int);

INSERT INTO Table1 VALUES (NULL, 'Joe', 'Bloggs');
INSERT INTO Table1 VALUES (NULL, 'Mike', 'Smith');
INSERT INTO Table1 VALUES (NULL, 'Jane', 'Doe');

INSERT INTO Table2 VALUES (NULL, 1, 1);
INSERT INTO Table2 VALUES (NULL, 1, 2);
INSERT INTO Table2 VALUES (NULL, 2, 2);
INSERT INTO Table2 VALUES (NULL, 3, 3);
INSERT INTO Table2 VALUES (NULL, 3, 4);

查询结果:

+----+------------+-----------+--------+
| id | first_name | last_name | job_id |
+----+------------+-----------+--------+
|  1 | Joe        | Bloggs    | 1,2    | 
|  2 | Mike       | Smith     | 2      | 
|  3 | Jane       | Doe       | 3,4    | 
+----+------------+-----------+--------+

请注意,在默认情况下,结果GROUP_CONCAT()是截断为1024的最大长度.但是,这可以设置为更大的值.如果需要修改它,请使用SET命令,如下所示:

SET GLOBAL group_concat_max_len = 2048;