How can I join 3 tables in MySQL?

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I have these 4 tables:

Suppliers(id_sup, name, city)
Companies( id_co, name, city)
Products(id_p, name, city)
Deliveries (id_sup, id_co, id_p)

in one query, I need to get a list of all cities (no duplicates) and for each, show the number of suppliers, companies, and products that can be found in that city.

In oracle SQL I would have used some Full OUTER JOIN. what's the alternative?

This is a suggested solution for joining 2 of the tables:

SELECT city                                          
     , COUNT(DISTINCT id_sup) Suppliers                   
     , COUNT(DISTINCT id_co) Companies                    
FROM ( SELECT COALESCE(s.city,c.city) city     
              , id_sup                           
              , id_co                            
         FROM Suppliers AS s                   
            LEFT OUTER JOIN Companies AS c ON c.city = s.city                  
         UNION                                   
         SELECT COALESCE(s.city,c.city) city     
              , id_sup                           
              , id_co                            
         FROM Suppliers AS s                   
            RIGHT OUTER JOIN Companies AS c ON c.city = s.city ) AS union_query

GROUP BY city 

How to add the final table Products to the mix?

Just use union all and group by:

select city, sum(is_supplier), sum(is_company),
       sum(is_product), sum(is_delivery)
from ((select city, 1 as is_suppler, 0 as is_company, 0 as is_product, 0 as is_delivery
       from suppliers
      ) union all
      (select city, 0 as is_suppler, 1 as is_company, 0 as is_product, 0 as is_delivery
       from companies
      ) union all
      (select city, 0 as is_suppler, 0 as is_company, 1 as is_product, 0 as is_delivery
       from products
      ) union all
      (select city, 0 as is_suppler, 0 as is_company, 0 as is_product, 1 as is_delivery
       from deliveries
      ) 
     ) c
group by city;

Or, even more simply in MySQL:

select city, sum(which = 'supplier'), sum(which = 'company'),
       sum(which = 'product'), sum(which = 'delivery')
from ((select city, 'suppler' as which from suppliers
      ) union all
      (select city, 'company' as which from companies
      ) union all
      (select city, 'product' as which from products
      ) union all
      (select city, 'delivery' as which from deliveries
      ) 
     ) c
group by city;

Joining three tables using MySQL, 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. 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 = 10200 times only. And thus, the performance went up!!!

With UNION get all the cities from all 3 tables and LEFT join to the results the 3 tables to finally aggregate:

select t.city,
  count(distinct s.id_sup) counter_suppliers,
  count(distinct c.id_co) counter_companies,
  count(distinct p.id_p) counter_products
from (
  select city from suppliers union  
  select city from companies union
  select city from products 
) t
left join suppliers s on s.city = t.city
left join companies c on c.city = t.city
left join products p on p.city = t.city
group by t.city

See a simplified demo.

How to join three tables in SQL query – MySQL , Joining multiple tables in SQL is always a tricky task, It can be more difficult if you need to join more than two tables in single SQL query, worry not. This article� Two approaches to join three or more tables: 1. Using joins in sql to join the table: The same logic is applied which is done to join 2 tables i.e. minimum number of join statements to join n tables are (n-1). Query: select s_name, score, status, address_city, email_id, accomplishments from student s inner join marks m on s.s_id = m.s_id inner

to get all cities, since we don't have a city table as a dimension, we can get the domain from each of the city columns from each of the three tables, and combine them with UNION set operator:

SELECT cs.city
  FROM suppliers cs
 GROUP BY cs.city 

 UNION

SELECT cc.city 
  FROM companies cc
 GROUP BY cc.city 

 UNION

SELECT cp.city
  FROM products cp
 GROUP BY cp.city

That should get us a list of distinct city values that appear in the three tables.

We could take that set, and do outer join operations to the individual tables. But that has the potential to generate cross product... if there are three suppliers related to a city and four companies related to the same city, we would generate a resultset of twelve rows.

To fix that, we could get a count of DISTINCT primary key values.

Or, we can pre-aggregate the results in inline views, returning a single row per city. That avoids the problem of semi-cartesian products.

Let's reference the query above in an line view in another query. We will alias it ci. (If we had a dimension table city, we could reference that,)

Something like this:

SELECT ci.city 
     , IFNULL(np.cnt_,0)   AS cnt_products
     , IFNULL(nc.cnt_,0)   AS cnt_companies
     , IFNULL(ns.cnt_,0)   AS cnt_suppliers

  FROM ( /* inline view query */ ) ci

  LEFT
  JOIN ( SELECT p.city
              , COUNT(1) AS cnt_
           FROM products p
          GROUP BY p.city
       ) np
    ON np.city = ci.city

  LEFT
  JOIN ( SELECT c.city
              , COUNT(1) AS cnt_
           FROM companies c
          GROUP BY c.city
       ) nc
    ON nc.city = ci.city

  LEFT
  JOIN ( SELECT s.city
              , COUNT(1) AS cnt_
           FROM suppliers s
          GROUP BY s.city
       ) ns
    ON ns.city = ci.city

 ORDER BY ci.city

(In place of /* inline view query */, use the SQL text from the first query, to generate the distinct list of city.)

How to join 3 tables in MySQL, This should be straightforward, probably something like this: SELECT u.UserID, o .OrderID, p.PassengerID FROM Users u JOIN Orders o ON u. As you can clearly see it has returned only those results which matches user_id and where messages is not null.. RIGHT JOIN. RIGHT JOIN joins the two tables in such a way that it returns all the value from the right and matched value from left tables and also return null on left table when there is no match found.

SQL JOIN, JOIN Syntax, JOIN Differences, 3 tables, A JOIN locates related column values in the two tables. A query can contain zero, one, or multiple JOIN operations. INNER JOIN is the same as JOIN; the keyword � As you can see we executed inner join for three tables and retrieved 2 columns: student.name and course.name. Note that result doesn’t contain nullable values. You can join 4 or even more SQL tables in the same way. If you want to filter the result by student name, for example, you can add WHERE clause at the end:

MySQL INNER JOIN, In MySQL the INNER JOIN selects all rows from both participating part of SELECT statements and multiple-table UPDATE and DELETE� MySQL LEFT JOIN clause. Similar to an inner join, a left join also requires a join-predicate. When joining two tables using a left join, the concepts of left and right tables are introduced. The left join selects data starting from the left table. For each row in the left table, the left join compares with every row in the right table.

MySQL, MySQL Inner-join for 3 tables. Example#. let's assume we have three table which can be used for simple website with Tags� In all three queries, table1 and table2 are the tables to be joined. You can join more than two tables. In both queries, col1 and col2 are the names of the columns being matched to join the tables. The tables are matched based on the data in these columns.

Comments
  • You will get better help here . If you can put together some dml and some sample inserts. I can take a stab at helping you with this , but odds are that I wont be precise because I cant see some sorta sample data.