I have three tables named
**Student Table**
-------------
id name
-------------
1 ali
2 ahmed
3 john
4 king
**Course Table**
-------------
id name
-------------
1 physic
2 maths
3 computer
4 chemistry
**Bridge**
-------------
sid cid
-------------
1 1
1 2
1 3
1 4
2 1
2 2
3 3
3 4
4 1
4 2
Now to show the student name with the course name which he had studied like,
**Result**
---------------------------
Student Course
---------------------------
ahmed physic
ahmed maths
ahmed computer
ahmed chemistry
ali physic
ali maths
john computer
john chemistry
king physic
king maths
I build following query
select s.name as Student, c.name as Course from student s, course c join bridge b on c.id = b.cid order by s.name
But it does not return the required result...
And what would be for normalized form, if I want to find who is manager over other:
**employee**
-------------------
id name
-------------------
1 ali
2 king
3 mak
4 sam
5 jon
**manage**
--------------
mid eid
--------------
1 2
1 3
3 4
4 5
And wants to get this result:
**result**
--------------------
Manager Staff
--------------------
ali king
ali mak
mak sam
sam jon
Use ANSI syntax and it will be a lot more clear how you are joining the tables:
SELECT s.name as Student, c.name as Course
FROM student s
INNER JOIN bridge b ON s.id = b.sid
INNER JOIN course c ON b.cid = c.id
ORDER BY s.name
Simply use:
select s.name "Student", c.name "Course"
from student s, bridge b, course c
where b.sid = s.sid and b.cid = c.cid
For normalize form
select e1.name as 'Manager', e2.name as 'Staff'
from employee e1
left join manage m on m.mid = e1.id
left join employee e2 on m.eid = e2.id
SELECT *
FROM user u
JOIN user_clockits uc ON u.user_id=uc.user_id
JOIN clockits cl ON cl.clockits_id=uc.clockits_id
WHERE user_id = 158
Don't join like that. It's a really really bad practice!!! It will slow down the performance in fetching with massive data. For example, if there were 100 rows in each tables, database server have to fetch 100x100x100 = 1000000 times. It had to fetch for 1 million times. To overcome that problem, join the first two table that can fetch result in minimum possible matching(It's up to your database schema). Use that result in Subquery and then join it with the third table and fetch it. For the very first join --> 100x100= 10000 times and suppose we get 5 matching result. And then we join the third table with the result --> 5x100 = 500. Total fetch = 10000+500 = 10500 times only. And thus, the performance went up!!!
join query with three tables and we want two values from the same column we set the alias name for every table in the joins. Same table name also declare as a different names.
const sql = `select p.ID,p.purchaseamount,urs.name as
buyername,pd.productname,
pd.amount,urs1.name as sellername
from purchases p
left join products pd on p.productid=pd.ID
left join users urs on p.userid=urs.ID
left join users urs1 on pd.userid=urs1.ID`
SELECT
employees.id,
CONCAT(employees.f_name," ",employees.l_name) AS 'Full Name', genders.gender_name AS 'Sex',
depts.dept_name AS 'Team Name',
pay_grades.pay_grade_name AS 'Band',
designations.designation_name AS 'Role'
FROM employees
LEFT JOIN genders ON employees.gender_id = genders.id
LEFT JOIN depts ON employees.dept_id = depts.id
LEFT JOIN pay_grades ON employees.pay_grade_id = pay_grades.id
LEFT JOIN designations ON employees.designation_id = designations.id
ORDER BY employees.id;
You can JOIN multiple TABLES like this example above.
Just adding a point to previous answers that in MySQL we can either use
table_factor syntax
OR
joined_table syntax
mysql documentation
Table_factor example
SELECT prd.name, b.name
FROM products prd, buyers b
Joined Table example
SELECT prd.name, b.name
FROM products prd
left join buyers b on b.bid = prd.bid;
FYI: Please ignore the fact the the left join on the joined table example doesnot make much sense (in reality we would use some sort of join table to link buyer to the product table instead of saving buyerID in product table).
Query for three table join and limit set
SELECT * FROM (SELECT t1.follower_userid, t2.*, t3.login_thumb, t3.login_name,
t3.bio, t3.account_status, t3.gender
FROM videos t2
LEFT JOIN follower t1
ON t1.follower_userid = t2.user_id
LEFT JOIN videos_user t3
ON t1.follower_userid = t3.login_userid
WHERE t1.following_userid='$userid'
LIMIT $startpoint , $limit) AS ID
ORDER BY ID DESC
Query to join more than two tables:
SELECT ops.field_id, ops.option_id, ops.label
FROM engine4_user_fields_maps AS map
JOIN engine4_user_fields_meta AS meta ON map.`child_id` = meta.field_id
JOIN engine4_user_fields_options AS ops ON map.child_id = ops.field_id
WHERE map.option_id =39 AND meta.type LIKE 'outcomeresult' LIMIT 0 , 30
Use this:
SELECT s.name AS Student, c.name AS Course
FROM student s
LEFT JOIN (bridge b CROSS JOIN course c)
ON (s.id = b.sid AND b.cid = c.id);
I have below database structure:
students table
id name gender
1 abc male
2 xyz female
subjects table
id name
1 maths
2 science
3 english
studentmarks
id st_id sub_id marks
1 1 1 20
2 1 2 30
3 2 1 40
I want result like this:
name subjects marks
abc maths 20
abc science 30
xyz maths 40
abc english 0
xyz science 0
xyz english 0
Is it possible to achieve above result with MySQL query alone?
I tried this query:
SELECT *
FROM students
LEFT JOIN studentmarks
ON studentmarks.std_id = students.id
LEFT JOIN subjects
ON subjects.id = studentmarks.sub_id
The result is not as I want, because I am using join so it will only return the matching id.
This may work
SELECT cr.st_name, cr.sub_name, COALESCE(c.marks, 0)
FROM (SELECT a.id st_id,
a.NAME st_name,
b.NAME sub_name,
b.id sub_id
FROM students a,
subjects b) cr
LEFT JOIN studentmarks c
ON cr.sub_id = c.sub_id
AND c.st_id = cr.st_id
Try that one
SELECT A.name, B.name, C.marks
FROM students A, subjects B, studentmarks C
WHERE A.id = C.st_id AND B.id = C.sub_id;
You can achieve the result using following query
SELECT SM.marks,
S.NAME AS Student_name,
SBJ.NAME as Subject
FROM studentmarks AS SM
JOIN students AS S ON SM.st_id = S.id
JOIN subjects AS SBJ ON SM.sub_id = SBJ.id
You can also use CROSS join as well I guess if you want to stick with your current query
I am trying to select whether or not an entry exists in another table. Here's a simple example:
Two tables:
Student
ID Major
1 CS
2 CS
3 CS
4 CS
Student_Teacher
SID TID
1 A
1 B
1 C
3 B
3 D
The first table has a list of student IDs (key = Student ID)
The 2nd table has a list of student -> teachers (key = Student ID, Teacher ID combination).
I would like to select ALL students (1,2,3,4; one in each row) and a flag for whether or not they have a teacher.
SELECTED:
ID Flag
1 1
2 0
3 1
4 0
I know this is possible to do using group by:
select Student.ID, count(Student_Teacher.TID)
from Student left join Student_Teacher
group by Student.ID
Is there a simpler way?
You can try joining to a derived table that contains the distinct student id values of the second table:
SELECT ID, IF(ST.SID IS NOT NULL, 1, 0) AS FLAG
FROM Student AS S
LEFT JOIN (
SELECT DISTINCT SID
FROM Student_Teacher
) AS ST ON S.ID = ST.SID
I have a table say Student . This has 2 columns studentid and classid
Anotehr table Class which has ClassID and ClassDescription
Assume , Class has values
ClassID ClassDescription
1 A
2 B
3 C
4 D
5 E
I want to create a query to find out students who have attended A and B . This should be a dynamic query so that next time I require a qry to find out students who have attended A, B and C or B, C and D I should be able to use it.
Create a new table filterClass to be your dinamic source like
FilterID
'A'
'B'
'C'
Then your query is
SELECT S.StudentID
FROM Student S
JOIN Class C
ON S.class_id = C.class_id
JOIN filterClass F
ON C.ClassDescription = F.FilterID
GROUP BY S.StudentID
HAVING COUNT(C.ClassDescription) = (SELECT COUNT(FilterID) FROM filterClass)
In this case SELECT COUNT(FilterID) FROM filterClass will be 3 (A,B,C)
I am planning to create a website similar to IMDB.com. To reduce execution time I am using the following structure. Is it okay for faster working?
Table - 1
Id Movie_name description
1 name one some description
2 name two some description
3 name three some description
Table 2
id actorname
1 name 1
2 name 2
3 name 3
4 name 4
Table 3
id movieid actorid
1 1 1
2 1 2
3 1 3
4 1 9
5 2 6
6 2 5
7 2 8
8 2 1
When I want to list actors in a movie program will retrieve actors ids from table 3 and find respective names from table 2 (using single query). When I want to list the movies of a actor it will retrieve movie ids from table 3 and find respective names from first table. Will it work properly? Any other ideas?
This will give all actors in a specified movie,
SELECT c.ID, c.actorName
FROM table1 a
INNER JOIN table3 b
ON a.ID = b.movieID
INNER JOIN table2 c
ON b.actorid = c.ID
WHERE a.ID = 1
This one will give all movies for a specified actor
SELECT a.*
FROM table1 a
INNER JOIN table3 b
ON a.ID = b.movieID
INNER JOIN table2 c
ON b.actorid = c.ID
WHERE c.ID = 1
SQLFiddle Demo (both queries)
To further gain more knowledge about joins, kindly visit the link below:
Visual Representation of SQL Joins
UPDATE 1
This is called Relational Division
SELECT a.ID, a.Movie_Name
FROM table1 a
INNER JOIN table3 b
ON a.ID = b.movieID
INNER JOIN table2 c
ON b.actorid = c.ID
WHERE c.ID IN (1, 2, 3)
GROUP BY a.ID, a.Movie_Name
HAVING COUNT(DISTINCT c.ID) = 3
SQL of Relational Division
I suggest that you modify table3 by taking away the id field. Use the movieid and actorid together as your primary key. You might want to add other fields to this table such as name of character and order of appearance as suggested in the comment by Jermaine Xu.