Mysql Select specific data from 2 tables base on the third table - php

Question

I have three tables
tbl_project
db_projectid db_projectname
1 test
2 xxx
tbl_activities
db_id db_projectid db_category
1 1 Civil Work
2 1 Mechanical
3 1 Electrical
tbl_dailypercentage
db_dpid db_aid db_projectid db_status
1 1 1 red
2 1 1
3 2 1
db_projectid is a primary key in tbl_project
db_id is a primary key and db_projectid is a foreign key in tbl_activities
db_dpid is a primary key and db_aid is a foreign key in tbl_dailypercentage
I tried this query
select
activities.db_id,
activities.db_category as cat,
dailypercentage.db_status,
dailypercentage.db_aid,
dailypercentage.db_projectid
from tbl_activities as activities,tbl_dailypercentage as dailypercentage
where
dailypercentage.db_projectid='$projectId'
and
activities.db_id=dailypercentage.db_aid
and
dailypercentage.db_status='red'
But i Have ab error
Undefined variable: cat
while($row=mysqli_fetch_array($statusQuery)){
$status=$row['db_status'];
$cat=$row['cat'];
}
<td> <?php if($cat=="Civil Work" && $status="red"){
echo"<p style='color:$status'>".($sumcivil/$civilCount)."</p>";}
else{echo ($sumcivil/$civilCount);}?>
</td>
I try also many thing the left join and the right join
to have the result i want
The Result i want is
For Project who have an id=1
category status
civil work red
mechanical work
electrical work
For Project who have an id=2
category status
civil work
mechanical work
electrical work

Answer 1

You showed this code:
while($row=mysqli_fetch_array($statusQuery)){
$status=$row['db_status'];
$cat=$row['cat'];
}
If your query returns no rows, $status and $cat will never get defined. I guess this is what went wrong. What happens if you run that query with a MySQL client like phpMyadmin?
Similarly, if your query returns more than one row, $status and $cat will capture the values of only the last row.
It's important to work out what you want to happen with no rows and multiple rows.

Answer 2

Based only on the tables in your question I have put together the following schema (I've not added constraints to the foreign keys as this is just for testing).
create table tbl_project (
`db_projectid` INT(11) UNSIGNED NOT NULL AUTO_INCREMENT,
`db_projectname` VARCHAR(255) NOT NULL DEFAULT 'Undefined',
PRIMARY KEY (`db_projectid`)
);
create table tbl_activities (
`db_id` INT(11) UNSIGNED NOT NULL AUTO_INCREMENT,
`db_projectid` INT(1) NOT NULL,
`db_category` VARCHAR(255) NOT NULL DEFAULT 'Undefined',
PRIMARY KEY (`db_id`)
);
create table tbl_dailypercentage (
`db_dpid` INT(11) UNSIGNED NOT NULL AUTO_INCREMENT,
`db_aid` INT(1) NOT NULL,
`db_projectid` INT(1) NOT NULL,
`db_status` VARCHAR(255) NULL,
PRIMARY KEY (`db_dpid`)
);
insert into tbl_project (db_projectname) values ('Test'), ('xxx');
insert into tbl_activities (db_projectid, db_category) values ('1', 'Civil Work'), ('1', 'Mechanical'), ('1', 'Electrical');
insert into tbl_dailypercentage (db_aid, db_projectid, db_status) values
('1', '1', 'red'),
('1', '1', null),
('2', '1', null);
select a.db_category as cat, dp.db_status from tbl_project p
left join tbl_activities a on p.db_projectid = a.db_projectid
left join tbl_dailypercentage dp on dp.db_aid = a.db_id
where p.db_projectid = 1
group by a.db_id;
I've had to add the group by into the final query as you have multiple rows in tbl_dailypercentage with the same db_aid and db_projectid values.
After that, you want to tweak your php code, putting the td stuff inside the while loop:
<?php while($row=mysqli_fetch_array($statusQuery)):?>
$status=$row['db_status'];
$cat=$row['cat'];
<td> <?php if($cat=="Civil Work" && $status="red"){
echo"<p style='color:$status'>".($sumcivil/$civilCount)."</p>";}
else{echo ($sumcivil/$civilCount);}?>
</td>
<?php endwhile; ?>