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 this Table (tblExample):
ID U_ID Title Desc Cat SubCat Country Date
----------------------------------------------------------------------------
1 2 Title1 Desc1 Orange Blue England 12/05/2015
2 3 Title2 Desc2 Orange Blue England 12/05/2015
3 2 Title3 Desc2 Orange Blue England 12/05/2015
I then have another table (tblRating):
ID U_ID rating
------------------
1 2 4
2 2 2
3 2 4
If I do an SQL statement like:
select e.*, r.*
from tblExample e
inner join tblRating r on e.U_ID = r.U_ID
The result I get is just the details of U_ID = 2, but I want to still show U_ID = 3, this is the user that has no record in tblRating. How can I do this? I tried left join but did not work.
Replace the inner join with a left join. This will give you all the relevant rows from tblExample and tblRating or nulls where tblRating does have a matching rows:
SELECT e.*, r.*
FROM tblExample e
LEFT JOIN tblRating r ON e.U_ID = r.U_ID
This is because of Join issue, when you perform INNER JOIN only the matching records from both table returns.
If you want to get all the records from first table and only the matching records from the second table then you need to perform LEFT JOIN.
select
first.*,
second.*
from tblExample first
LEFT JOIN tblRating second on first.U_ID = second.U_ID
For the second table it will return NULL in case of not matching conditions.
You can also refer this question about difference between JOINS,
I've got the following tables:
Articles:
Nr Name Price
1011 DU 10
1012 DA 5
1013 DO 20
Clients
Nr Name Street Zip
123 John ... ...
234 Will ... ...
Orders
Nr Client_Nr Art_Nr Quantity
1 123 1011 1
2 123 1012 2
3 234 1012 2
4 234 1013 5
To know the total sum of orders per customer,
I use the following statement:
SELECT Clients.Name,
SUM(Orders.Quantity * Article.Price) AS "Total"
FROM Orders
LEFT OUTER JOIN Articles
ON Orders.Art_Nr = Articles.Nr
LEFT OUTER JOIN Clients
ON Orders.Client_Nr = Clients.Nr
GROUP BY Clients.Name;
Is left outer joins used when there are rows in one table that may not be referenced in the second table.
What is the better way of writing the above query?
Can I do this:
SELECT clients.name, SUM(orders.quantity * articles.price)
FROM orders
INNER JOIN articles ON orders.art_nr = articles.nr
INNER JOIN clients ON orders.client_nr = clients.nr
GROUP BY clients.name;
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.
My tables
product
pid name
1 AA
2 bb
3 cc
History table
hid pid uid
1 1 1
2 1 2
3 1 1 // this one should join with pid 1
4 3 2 // this one should join with pid 3
5 2 3
6 2 1 // this one should join with pid 2
I like to display most recent bidder on a product.The history tables stores bidder
details.if no bid on product just need to return null.
Thanks
How about something like
SELECT *
FROM product p LEFT JOIN
(
SELECT ht.*
FROM History_table ht INNER JOIN
(
SELECT pid,
MAX(hid) last_hid
FROM History_table ht
GROUP BY pid
) lstItem ON ht.pid = lstItem.pid
AND ht.hid = lstItem.last_hid
) ht ON p.pid = ht.pid
First you need to retrieve the MAX hid per pid, which by definition should be the most recent entry.
Then join that back to the same history table to retrieve the uid.
And lastly join this (LEFT JOIN) back to the actual products table.
Hope that helps.