MySQL Nested Select可以返回结果列表吗 [英] Can MySQL Nested Select return list of results

问题描述

我想编写一条mysql语句，该语句将返回一个表的结果列表以及用逗号分隔的另一表的字段列表.我认为一个例子可能会更好地解释它

I want to write a mysql statement which will return a list of results from one table along with a comma separated list of field from another table. I think an example might better explain it

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

我想返回一个用逗号分隔的job_ids列表的人.所以我的结果集将是

I want to return a list of people with a comma separated list of job_ids. So my result set would be

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

但是显然这是行不通的，因此需要将(将表2中的select job_id从表2中选择)作为job_id"部分更改.

but obviously this does not work so need to change the '(SELECT job_id FROM Table 2) as job_id' part.

希望这很有意义

谢谢 约翰

推荐答案

您可能要使用

You may want to use the GROUP_CONCAT() function, as follows:

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;

让我们用您的示例数据对其进行测试:

Let's test it with your example data:

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，默认情况下，GROUP_CONCAT()的结果为截断为最大长度1024 .但是，可以设置为更大的值.如果需要修改，请使用SET命令，如下所示:

Note that by default, the result of GROUP_CONCAT() is truncated to the maximum length of 1024. However this can be set to a much larger value. Use the SET command if you require to modify it, as follows:

SET GLOBAL group_concat_max_len = 2048;

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