Mysql 一对多连接，行到列

Question

我在 MySql 数据库中有 2 个 table 名为 con01_objects 和 con01_object_contacts。他们有如图所示的外键 (con01_objects.id = con01_object_contacts.obj_id).

image

如您所见，con01_object_contacts table 包含 contact_type 列，其中将有多个一个对象的联系人类型及其对应的联系人（联系人类型：0-number, 1-web, 2-tolfree, 3- facebook, 4-twitter, 5-instagram, 6-youtube, 7- mail）。

我需要的是加入这2个table，这样就不会出现重复的对象了。我需要一个联合结果，它将每个联系人类型显示为一列。如果相应联系类型中的对象没有联系，则该条目应为 NULL。

+++++++++++++++++++++++++++++++++++++++++++++ ++++++++++++++++++

objects--- contype_0(num)---- contype1(WEB) ----- contype(tolfree) ++++++++++++++++++++++++++++++++++++++++++++++++++++ +++++++++++++

obj1 ---- +96785445578700 ---- SOMETHING.c0M ----- 45469889

obj2 ---- +55457875748787 ------ NULL ---------------------- 42499898

我试过这个查询，但它 returns 重复行，因为一个对象具有不同的联系人类型。 :

SELECT * FROM con01_objects LEFT JOIN con01_object_contacts ON con01_objects.id= con01_object_contacts.obj_id

先谢谢了。

Answer 1

我想你正在寻找这个：

Select distinct(a.jid), 
(SELECT contact FROM con01_object_contacts where contact_type = '0') as contype_0, 
(SELECT contact FROM con01_object_contacts where contact_type = '1') as contype_1,
(SELECT contact FROM con01_object_contacts where contact_type = '2') as contype_2
from con01_objects a
left join con01_object_contacts as b
on a.id = b.obj_id;

Mysql 一对多连接，行到列

Mysql one to many join, rows to columns

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