Php 从两个具有总成本的表中选择全部

我尝试从mysql数据库的两个表中选择全部，总成本的总和在第二个表中 我有一个表名

tbl_project

contain

db_id   db_projectname  db_totalcost
1        test            200
2        test            300
3        test2           800

db\u id db\u projectname

和其他列

 1        test
 2        test2
 3        test3

第二个表名

tbl_活动

contain

db_id   db_projectname  db_totalcost
1        test            200
2        test            300
3        test2           800

我想要的是

test  500
test2 800
test3  

我尝试了这个查询，但没有给出那个结果

    select tbl_project.db_id, tbl_project.db_projectname,tbl_project.db_location,tbl_project.db_client,tbl_project.db_transferredto,tbl_project.db_psd,tbl_project.db_pdd,tbl_project.db_duration,tbl_project.db_past,tbl_project.db_padd,tbl_project.db_aduration,tbl_project.db_percent,tbl_project.db_pnote,tbl_project.db_user,tbl_project.db_cpercentage,tbl_project.db_epercentage,tbl_project.db_mpercentage,tbl_project.db_status,tbl_project.db_offer,tbl_project.db_sheet,tbl_project.db_invoice,tbl_project.db_po,sum(tbl_activities.db_totalcost) as total_cost from tbl_project,tbl_activities where 
tbl_project.db_projectname=tbl_activities.db_projectname

它给我

---

测试但只测试另一个项目和一个项目的总和，而不是所有项目

您需要使用

左加入和分组方式

SELECT
    tbl_project.db_id,
    tbl_project.db_projectname,
    tbl_project.db_location,
    tbl_project.db_client,
    tbl_project.db_transferredto,
    tbl_project.db_psd,
    tbl_project.db_pdd,
    tbl_project.db_duration,
    tbl_project.db_past,
    tbl_project.db_padd,
    tbl_project.db_aduration,
    tbl_project.db_percent,
    tbl_project.db_pnote,
    tbl_project.db_user,
    tbl_project.db_cpercentage,
    tbl_project.db_epercentage,
    tbl_project.db_mpercentage,
    tbl_project.db_status,
    tbl_project.db_offer,
    tbl_project.db_sheet,
    tbl_project.db_invoice,
    tbl_project.db_po,
    sum(
        tbl_activities.db_totalcost
    ) AS total_cost
FROM
    tbl_project
LEFT JOIN tbl_activities ON tbl_project.db_projectname = tbl_activities.db_projectname
GROUP BY tbl_project.db_id

---

注意：

使用

aggregate

函数（例如SUM、COUNT..），而不使用

groupby

将结果集压缩为一行。

尝试此操作

SELECT 
db_projectname.db_projectname,SUM(tbl_activities.db_totalcost) AS total_cost 
FROM db_projectname
LEFT JOIN tbl_activities 
ON 
db_projectname.db_projectname = tbl_activities.db_projectname
GROUP BY db_projectname.db_projectname

---

选择的字段比所需输出中的字段多得多-是否需要选择所有字段？我不确定，但我认为您应该按“db_projectname”分组。因为db_id将有不止一个。