I have a database with 3 tables: students, courses and mistakes. I have one joining table (csm) where I connect the 3 tables. I am supposing mistakes are the same for each course.
Table Courses
+----------+---------------+
| crs_id | crs_name |
+----------+---------------+
| 1 | HTML |
| 2 | PHP |
| 3 | Python |
+----------+---------------+
Table Students
+----------+---------------+---------------+
| stu_id | stu_firstname | stu_lastname |
+----------+---------------+---------------+
| 1 | Tina | Turner |
| 2 | Lisa | Laroi |
| 3 | Dina | Donna |
| 3 | Jim | Leduc |
+----------+---------------+---------------+
Table Mistakes
+----------+---------------+------------+
| mis_id | mis_name | mis_weight |
+----------+---------------+------------+
| 1 | No camelCase | 7 |
| 2 | No brackets | 10 |
| 3 | Operator mist.| 12 |
+----------+---------------+------------+
Joining table CSM
+----------+------------+------------+------------+
| csm_id | fk_crs_id | fk_stu_id | fk_mis_id |
+----------+------------+------------+------------+
| 1 | 1 | 1 | 1 |
| 2 | 1 | 1 | 3 |
| 3 | 2 | 3 | 1 |
| 4 | 3 | 2 | 2 |
| 5 | 3 | 2 | 1 |
| 6 | 3 | 3 | 1 |
+----------+------------+------------+------------+
If I select a specific course, I want to get a list of ALL students with the minus points for this course. So I also want to get the students with no result in the joining table csm.
The closest result I got is with the following sql statement:
select stu_firsname, stu_lastname, csm.*, sum(mis_weight)
from students s
left join crs_stu_mis csm on s.stu_id = csm.fk_stu_id
left join mistakes m on csm.fk_mis_id = m.mis_id
where fk_crs_id = 4 or fk_crs_id is null
group by stu_firstname;
With this I get the sum of the mistakes for a certain course and also the students who don't have any records in CSM table, but some results are missing. For example, this doesn't show the students who have records in the CSM table, but not for the requested course.
How do I get these students in my result table?
In your query :
left join crs_stu_mis csm on s.stu_id = csm.fk_stu_id`
...
where fk_crs_id = 4 or fk_crs_id is null
This is not exactly what you want, since this condition will filter out students that have records in the csm table for only courses other than 4. You want to move that condition to the corresponding LEFT JOIN:
left join crs_stu_mis csm on s.stu_id = csm.fk_stu_id AND csm.fk_crs_id = 4
Another potential source of problems is the way the query handles aggregation. There are non-aggregated columns in the SELECT clause that do not appear in the GROUP BY clause. This syntax is not good SQL coding practice, and is not supported anymore since version 5.7 of MySQL. I assumed that you want to one record in the result for each student.
Query:
select
s.stu_firstname,
s.stu_lastname,
sum(m.mis_weight) total_misses_weight
from
students s
left join crs_stu_mis csm on s.stu_id = csm.fk_stu_id AND csm.fk_crs_id = 3
left join mistakes m on csm.fk_mis_id = m.mis_id
group by
s.stu_id,
s.stu_firstname,
s.stu_lastname
Demo on DB Fiddle for course id 3:
| stu_firstname | stu_lastname | total_misses_weight |
| ------------- | ------------ | ------------------- |
| Tina | Turner | |
| Lisa | Laroi | 17 |
| Dina | Donna | 7 |
| Jim | Leduc | |
if your primary data's is in CSM table, try this:
select s.stu_firsname, s.stu_lastname, csm.*, sum(m.mis_weight) from crs_stu_mis csm
join students s on s.stu_id = csm.fk_stu_id
join mistakes m on csm.fk_mis_id = m.fou_id
csm.fk_crs_id = 4
group by s.stu_naam;
Second case:
Your data's can affected by group by attribute, try attribute that it is not NULL , ex:
select s.stu_firsname, s.stu_lastname, csm.*, sum(m.mis_weight) from crs_stu_mis csm
join students s on s.stu_id = csm.fk_stu_id
join mistakes m on csm.fk_mis_id = m.fou_id
csm.fk_crs_id = 4
group by csm.csm_id;
Related
I have two tables users and services and i am try to write a single query that will create a new column skills. The values in the column skills will be the service_title which maps to the service_id stored in user_skills.
Below are the examples of a the tables used:
Table users:
+---------+---------------+----------------+----------------+
| id | user_fname | user_lname | user_skills |
+---------+---------------+----------------+----------------+
| 1 | kiran | bhattarai | 1,2 |
| 2 | sujan | bhattarai | 2,4 |
| 3 | manorath | dad | 1,2,3,4 |
| 4 | bhagawoti | mom | 2,3 |
+---------+---------------+----------------+----------------+
Table services:
+-----------------+------------------+
| service_id | service_title |
+-----------------+------------------+
| 1 | cook |
| 2 | clean |
| 3 | grocessery |
| 4 | teach |
+-----------------+------------------+
Currently i am using this query:
SELECT users.user_fname,
users.user_lname,
(SELECT GROUP_CONCAT(service_title)
FROM `services`
WHERE `service_id` IN (1,2,3,4)) as skills
FROM users
WHERE
id =3;
Result of the above query:
+---------------+----------------+----------------------------------------+
| user_fname | user_lname | skills |
+---------------+----------------+----------------------------------------+
| manorath | dad | cook,clean,grocessery,teach |
+---------------+----------------+----------------------------------------+
Instead of using the IN (1,2,3,4) I tried IN (users.user_skills) because the values in user_skills changes all the time and the result was:
+---------------+----------------+----------------------------------------+
| user_fname | user_lname | skills |
+---------------+----------------+----------------------------------------+
| manorath | dad | cook |
+---------------+----------------+----------------------------------------+
Every time a new service is added i have to add that service_id in the IN (1,2,3,4,new service id) of my query which is not a proper solution. I have already tried using php and another query to do solve this, the disadvantage of doing that is it is slowing down the process. How should i solve this problem in a single query.
You can use FIND_IN_SET() to JOIN the two tables.
SELECT
u.user_fname,
u.user_lname,
GROUP_CONCAT(s.service_title) as skills
FROM users u
LEFT JOIN services s
ON FIND_IN_SET(s.service_id, u.user_skills)
WHERE u.id = 3
Note that a JOIN with a FIND_IN_SET() condition cannot utilize any index. And that can lead to poor performance.
In general it's a bad idea to store relations in a separated string column. See Is storing a delimited list in a database column really that bad?.
You should normalize your design and create a separate table for your many-to-many relation. The table would look like
Table users_services:
+---------+------------+
| user_id | service_id |
+---------+------------+
| 1 | 1 |
| 1 | 2 |
| 2 | 2 |
| 2 | 4 |
| 3 | 1 |
| 3 | 2 |
| 3 | 3 |
| 3 | 4 |
| 4 | 2 |
| 4 | 3 |
+---------+------------+
And the query would be
SELECT
u.user_fname,
u.user_lname,
GROUP_CONCAT(s.service_title) as skills
FROM users u
LEFT JOIN users_services us ON us.user_id = u.id
LEFT JOIN services s ON s.service_id = us.service_id
WHERE u.id = 3
I need a help with mySQL SELECT query from multiple tables. I have got four tables: school, discipline, pupils and teams.
School table looks like:
+------+---------+---------------+----------+
| id | name | discipline_id | pupil_id |
+------+---------+---------------+----------+
| 1 | one | 2 | 5 |
+------+---------+---------------+----------+
| 2 | two | 3 | 8 |
+------+---------+---------------+----------+
| 3 | three | 4 | 12 |
+------+---------+---------------+----------+
Discipline table looks like:
+------+---------+
| id | name |
+------+---------+
| 1 | math |
+------+---------+
| 2 | bio |
+------+---------+
| 3 | liter |
+------+---------+
| 4 | geo |
+------+---------+
Teams table looks like:
+------+---------+---------------+-----------+
| id | name | school_id | member_id |
+------+---------+---------------+-----------+
| 1 | T1 | 1 | 3 |
+------+---------+---------------+-----------+
| 2 | T2 | 3 | 3 |
+------+---------+---------------+-----------+
| 3 | T3 | 2 | 9 |
+------+---------+---------------+-----------+
The result of disciplines I need to get with a "SELECT from discipline..." query by "member_id = 3" is:
+-----------------+---------------+
| discipline_name | discipline_id |
+-----------------+---------------+
| bio | 2 |
+-----------------+---------------+
| geo | 4 |
+-----------------+---------------+
By matching member's school and then getting its discipline, if it makes sense...Is it possible to do with just one mySQL query?
Type of: member_id 3 => school_id 1,3 => discipline_id = show related disciplines names and ids which are 2, 4
Thank you very much...
Your goal is not clear or makes no sense to me.
But here is what you are literally asking for:
SELECT
s.discipline_id
d.name
FROM teams t
LEFT JOIN school s
ON s.id = t.school_id
LEFT JOIN discipline d
ON d.id = s.discipline_id
WHERE t.member_id = 3
I have three tables. Two of them are separate irrelevant tables (students and subjects), the third (entries) is one which links them both with foreign keys (student_id and subject_id).
Here are all the tables with the records:
students:
+------------+------------+-----------+---------------------+---------------------+
| student_id | first_name | surname | email | reg_date |
+------------+------------+-----------+---------------------+---------------------+
| 1 | Emily | Jackson | emilym#gmail.com | 2012-10-14 11:14:13 |
| 2 | Daniel | ALexander | daniela#hotmail.com | 2014-08-19 08:08:23 |
| 3 | Sarah | Bell | sbell#gmail.com | 1998-07-04 13:16:32 |
| 4 | Alex | Harte | AHarte#hotmail.com | 1982-06-14 00:00:00 |
+------------+------------+-----------+---------------------+---------------------+
subjects:
+------------+--------------+------------+----------------+
| subject_id | subject_name | exam_board | level_of_entry |
+------------+--------------+------------+----------------+
| 1 | Art | CCEA | AS |
| 2 | Biology | CCEA | A |
| 3 | Computing | OCR | GCSE |
| 4 | French | CCEA | GCSE |
| 5 | Maths | OCR | AS |
| 6 | Chemistry | CCEA | GCSE |
| 7 | Physics | OCR | AS |
| 8 | RS | CCEA | GCSE |
+------------+--------------+------------+----------------+
entries:
+----------+---------------+---------------+------------+
| entry_id | student_id_fk | subject_id_fk | entry_date |
+----------+---------------+---------------+------------+
| 1 | 1 | 1 | 2012-10-15 |
| 2 | 1 | 4 | 2011-09-21 |
| 3 | 1 | 3 | 2015-08-10 |
| 4 | 2 | 6 | 1992-07-13 |
| 5 | 3 | 7 | 2013-02-12 |
| 6 | 3 | 8 | 2016-01-14 |
+----------+---------------+---------------+------------+
How would I go about selecting the names of all the students (students.first_name), and the name (subjects.subject_name) of whichever subject entries they have? What I mean is that all student names are returned, and all the subject names for their entries listed beside them, with NULL for those which don't have any entries. I also want it grouped by the first_name alphabetically.
I want the output to be something like:
first_name subject_name
--------------------------
Alex NULL
Daniel Chemistry
Emily French
Emily Computing
Sarah Physics
Sarah RS
though I'm not sure if that's entirely correct.
My guess is it's like this:
SELECT students.first_name, subjects.subject_name
FROM students
JOIN entries ON entries.student_id_fk = students.student_id
JOIN subjects ON entries.subject_id_fk = subjects.subject_id
GROUP BY students.first_name;
Really the only thing I'm not sure about is which join to use and where to put it, or if the tables need to be listed in a different order. I'm thinking it should be a left join but I'm not sure.
Help is much appreciated!
You should use left join since you want to return also row for student that has no subject assigned. Plus you want to sort the result, not group. So in the end should be like this:
SELECT students.first_name, subjects.subject_name
FROM students
LEFT JOIN entries ON entries.student_id_fk = students.student_id
LEFT JOIN subjects ON entries.subject_id_fk = subjects.subject_id
ORDER BY students.first_name;
I think this could be the query but use order by and not group by (group by is for aggregate function like count() or max() )
SELECT students.first_name, subjects.subject_name
FROM entries
LEFT JOIN students ON entries.student_id_fk = students.student_id
LEFT JOIN subjects ON entries.subject_id_fk = subjects.subject_id
ORDER BY students.first_name;
You likely want a LEFT OUTER JOIN:
select stu.first_name, sub.subject_name
from students stu
join entries e
on stu.student_id = e.student_id_fk
left outer join subjects sub
on sub.subject_id = e.subject_id_fk
order by stu.first_name;
I'm away from my PC with any SQL installed, so this is untested, but should give you what you want.
Modified my answer to replace the group by with an order by as pointed out by the others. That is the proper way to do it, unless the group is there as part of a larger query that you may have trimmed out.
Left join students table on the remaining two tables sequentially is the right choice to grab all the students first name.
To order the names order by should be used.
I have create a sql fiddle for better visualization of how to get the desired output.
Here is the link: http://sqlfiddle.com/#!9/a1c850/7
The query is
select students.student_name, subjects.subject_name
from
students
left join entries on entries.student_id=students.student_id
left join subjects on entries.subject_id=subjects.subject_id
order by students.student_name;
i have this two tables and i need to select everything from ENT table and display the name of the skill not the ID.
skill_1, skill_2, skill_3 refer to idSkill from skill table
Thank for you help
Ent Table :
+-------+---------+---------+---------+---------+
| idEnt | nameEnt | skill_1 | skill_2 | skill_3 |
+-------+---------+---------+---------+---------+
| 1 | testA | 1 | 2 | 3 |
| 2 | testB | 4 | 5 | 6 |
+-------+---------+---------+---------+---------+
Skill Table :
+---------+-------------+
| idSkill | nameSkill |
+---------+-------------+
| 1 | Storekeeper |
| 2 | Designer |
| 3 | Teacher |
| 4 | Baker |
| 5 | Gardener |
| 6 | Secretary |
+---------+-------------+
With this table structure you need to join the skill table 3 times on ent table, every time with different alias:
select idEnt, nameEnt, s1.nameSkill as skill1Name, s2.nameSkill as skill2Name, s3.nameSkill as skill3Name
from ent e
inner join skill s1 on e.skill_1=s1.idSkill
inner join skill s2 on e.skill_2=s2.idSkill
inner join skill s3 on e.skill_3=s3.idSkill
You may want to consider changing your table structure and have a connection table between ent and skill tables that hold idEnt - idSkill pairs.
Lets say that I have something table like this:
<b>Name</b>
+---------+--------+
| name_id | name |
+---------+--------+
| 5 | Betti |
| 6 | Derry |
| 7 | Alfred |
| 8 | Elsie |
| 9 | Cinta |
+---------+--------+
<b>Goods</b>
+----------+-----------+
| goods_id | goods |
+----------+-----------+
| 1 | Computer |
| 2 | AC |
| 3 | Microwave |
| 4 | TV |
+----------+-----------+
<b>Transaction</b>
+-------+---------+----------+
| ai_id | name_id | goods_id |
+-------+---------+----------+
| 1 | 7 | 2 |
| 2 | 5 | 4 |
| 3 | 9 | 3 |
+-------+---------+----------+
I want to replace name_id column on Transaction table with name column on Name table with corresponding name_id column and so for goods_id to produce something similar to this table:
<b>Transaction</b>
+-------+--------+-----------+
| ai_id | name | goods |
+-------+--------+-----------+
| 1 | Alfred | AC |
| 2 | Betti | TV |
| 3 | Cinta | Microwave |
+-------+--------+-----------+
If you're looking to just display the information rather than actually "replacing" your tables with new ones, then you could use a SELECT query with a simple INNER JOIN. This way you can display columns from multiple tables.
SELECT T.ai_id, N.Name, G.goods
FROM Transaction T
INNER JOIN Name N ON N.name_id = T.name_id
INNER JOIN Goods G ON G.goods_id = T.goods_id;
Try with inner join
SELECT T.ai_id,N.name,G.goods
FROM Transaction as T
INNER JOIN Goods as G ON T.goods_id = G.goods_id
INNER JOIN Name as N ON N.name_id = T.name_id;
Try this one
select tb3.ai_id,tb2.name,tb1.goods from Goods tb1,Name tb2,Transaction tb3 where tb3.name_id=tb2.name_id and tb3.goods_id=tb1.goods_id order by tb3.ai_id
try this:
SELECT C.ai_id,A.name,B.goods
FROM Transaction C
INNER JOIN Name A
ON A.name_id=C.name_id
INNER JOIN Goods B
ON B.goods_id=C.goods_id;
http://sqlfiddle.com/#!2/3c5f3/8