我正在处理将采用表的查询,并使用动态SQL将其作为数据透视表加入。我已经在Stack Overflow以及其他互联网上阅读了一些问题,并且无法找到我想要完成的解决方案。
我有一张像这样的桌子
+---------------------------------------+
| ID First_name Last_name owner |
+---------------------------------------+
| 1 Joe Bob 1 |
| 2 Fluffy Bob 0 |
| 3 Killer Bob 0 |
| 4 Bob Joe 1 |
| 5 Yapper Bob 0 |
+---------------------------------------+
这样的连接表就是这样(不要问我为什么它会自己加入,我没有设计它)
+-----------------------------------+
| contact_id relation_contact_id |
+-----------------------------------+
| 1 2 |
| 1 3 |
| 4 5 |
+-----------------------------------+
因此,每个用户都有可能拥有一只或多只宠物。我需要的枢轴是每个所有者的宠物名称,我希望它被编号(即Pet1_name,Pet2_name等)像这样
+---------------------------------------------------+
| First_name Last_name Pet1_name Pet2_name |
+---------------------------------------------------+
| Joe Bob Fluffy Killer |
| Bob Joe Yapper NULL |
+---------------------------------------------------+
我在这里遇到的主要问题是让数字正常运行。目前,它在每行之后不会重置为0,因此我将获得一堆空条目。使用上面的数据,这是我的结果集当前的样子:
+----------------------------------------------------------------+
| First_name Last_name Pet1_name Pet2_name Pet3_name |
+----------------------------------------------------------------+
| Joe Bob Fluffy Killer NULL |
| Bob Joe NULL NULL Yapper |
+----------------------------------------------------------------+
这是我正在运行的SQL
SET @sql = NULL;
SET @counter = 0;
Select GROUP_CONCAT(distinct
CONCAT('MAX(case when c2.id = ''', cc.relation_contact_id,
''' AND c.id = ''', cc.contact_id, '''
then c2.first_name end) AS ', CONCAT('`Pet_', @counter := @counter + 1, '_Name`')
)) INTO @sql
From contacts_contacts as cc;
SET @counter = 0;
SET @sql = CONCAT('SELECT c.id, c.first_name, c.last_name, c.email, ', @sql, '
FROM contacts c
LEFT JOIN contacts_contacts cc on c.id = cc.contact_id
LEFT JOIN contacts c2 on c2.id = cc.relation_contact_id
WHERE c.owner = 1
GROUP BY c.id
');
PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
这是一个SQLFiddle,其中有一个工作示例。
提前感谢您的帮助,期待这项工作!
答案 0 :(得分:0)
我得到了它来处理这个查询,但它有点性能,所以我可能会切换到PHP。在this question上找到了我的答案,所以有人可以将其标记为Dupe,如果他们愿意的话。
与此同时,这里有link to the updated SQLFiddle查询有效。
SET @sql = NULL;
Select
GROUP_CONCAT(distinct
CONCAT('max(case when rownum = ',
rownum,
' then c2.first_name end) AS Pet_', rownum, '_Name'
)
) INTO @sql
from
(
select contact_id, relation_contact_id,
@row:=if(@prev=contact_id, @row,0) + 1 as rownum,
@prev:=contact_id
from contacts_contacts, (SELECT @row:=0) r
) cc;
SET @sql = CONCAT('SELECT c.id, c.first_name, c.last_name, c.email as e, ', @sql, '
FROM
(
select contact_id, relation_contact_id,
@row:=if(@prev=contact_id, @row,0) + 1 as rownum,
@prev:=contact_id
from contacts_contacts, (SELECT @row:=0) r
) cc
LEFT JOIN contacts c on c.id = cc.contact_id
LEFT JOIN contacts c2 on c2.id = cc.relation_contact_id
WHERE c.owner = 1
GROUP BY e
');
PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
答案 1 :(得分:-1)
here中的存储过程将为您生成SQL。