I have 3 Tables: Jobs, Users, Applications.
I'd like a list of all jobs and optionally "any" applications submitted per each job but only if I have data for the user who submitted the application.
I vaguely remember seeing some obscure syntax in which 2 tables are joined to a query as if being a single table, something like:
select j.title, a.id, u.name from jobs j
left join applications a join users u on a.job_id=j.id and a.user_id = u.id
I know I could accomplish this with a subquery, but does a syntax of this nature exist?
Update
The answers I've received so far assume I want only a basic join. Though they break the intended logic posed in the question. Perhaps I've should've posted the subquery equivalent to illustrate the type of query I'd like to run.
select j.job_id, au.application_id, au.user_id from jobs j
left join (
select a.job_id, u.user_id from applications a
join users u on u.user_id = a.user_id
) au on j.job_id = au.job_id
You need both of these to be outer joins if you chain them the "simple" way:
select *
from jobs j
left outer join application a on a.job_id = j.id
left outer join users u on u.user_id = a.id
Since I take it that an application requires a user you can force the inner join to happen first in this way. Maybe that's the syntax question you were asking about. The parens are generally optional in my experience but I don't know a lot of MySQL:
select *
from jobs j
left outer join (application a
inner join users u on a.user_id = u.id) on a.job_id = j.id
This is where a right join comes up sometimes so the query can be written from top to bottom without any nesting:
select *
from application a
inner join users u on u.user_id = a.id on
right outer join jobs j on a.job_id = j.id
You were almost there, your only mistake was to put the both join conditions after the second join.
select *
from jobs j
left join application a on on.job_id = j.id
left join users u on u.user_id = u.id
Note that the maximum number of tables that can be referenced in a join is 61 (in MySQL and probably most of the popular DBMS).
See documentation.
Related
I am stuck with some SQL query.
I have four tables. Which are connected:
user =>user_account=>acount_profile_entries=>profile_entries
From left to right they are one to many.
user_account has a user_id field as FK.
account_profile_field has user_account_id and profile_entry_id.
Profile_entries has a text field that I need to show for each user (account).
I need to write a query that will show me, all accounts for every user, and its profile entries.
I am sorry if this is confusing, I tried to make it simple
This is what I have done so far. I can show all accounts for every user and this is the point I am stuck with. Last two commented out Joins are not working properly. I believe I am close somewhat, I just need a push :)
SELECT
u.email AS Email,
u.id AS UserId,
ua.id AS UserAccountId,
ua.app_id AS Application
FROM users AS u
INNER JOIN user_accounts ua ON ua.user_id = u.id
-- INNER JOIN account_profile_entries ape ON ape.user_account_id = ua.id
-- INNER JOIN profile_entries as pe ON pe.id = ape.profile_entry_id
limit 10
Try this SQL Query with using LEFT JOIN
Description :- The MySQL LEFT JOIN joins two tables and fetches rows based on a condition, which is matching in both the tables and the unmatched rows will also be available from the table written before the JOIN clause.
SYNTAX
SELECT column_name(s)
FROM table1
LEFT JOIN table2 ON table1.column_name = table2.column_name;
SELECT u.*,
u.id AS UserId,
ua.id AS UserAccountId,
ua.app_id AS Application,pe.* FROM `users` u
LEFT JOIN user_accounts ua ON ua.user_id = u.id
LEFT JOIN account_profile_entries ape ON ape.user_account_id = ua.id
LEFT JOIN profile_entries as pe ON pe.id = ape.profile_entry_id LIMIT 10
I have three mySQL-tables like this:
client network activities
\_id \_id \_id
\_name \_name \_client_id
\_[...] \[...] \_[...]
\_network_id
Now I want to have the following result:
client.*, network.name, number_of_activities_for_each_client
Actually I have this select-statement:
select client.*, network.name
from client
left join network
on client.network_id = network.id
How do I extend the statement? I would also like to see all clients.
SELECT c.*, n.name, COUNT(a.id) number_of_activities_for_each_client
FROM clients c
LEFT JOIN network n
ON n.id = c.network_id
LEFT JOIN activities a
ON a.client_id = c.id
GROUP BY c.id
Suppose we have this model:
As you see industry_id can be null. Can I fetch industry.name (if any), user.description, profile.name and project.title (all project titles) he/she has with a single MySQL query while having user.id?
Yes, JOIN the two tables:
SELECT
i.name,
u.id
FROM Industry AS i
LEFT JOIN `User` AS u ON u.industry_id = i.industry_id;
Update:
For multiple tables:
SELECT
i.Name AS InustryName,
p.Name AS UserName,
u.Description,
j.title AS ProjectTitle
FROM Industry AS i
INNER JOIN User AS u ON i.id = u.id
INNER JOIN Profile AS p ON p.user_id = u.id
INNER JOIN Project AS j ON u.id = j.user_id;
Note that: I used INNER JOIN between the tables, this will give you only the matched rows from the joined tables, you might need to use LEFT JOIN instead of innner join to include the untmatched rows, i.e., to get those industries that has no entries in the other tables. See this blog post:
A Visual Explanation of SQL Joins
i have a problem with sql query.
I need to get list of users. The problem is the left join i use.
this is my query
SELECT
u.*
FROM
users u LEFT JOIN game g on g.user_id = u.user_id
LEFT JOIN game_actions ga on ga.game_id = g.id
LEFT JOIN emails e on e.id = ga.email_id
WHERE
u.user_id = 0
AND u.is_contact_by_email = 1
AND email.type = 2
this query returns the same user more then once because of the join with other tables
i want this query to return each user just one time.
i'm using sql developer.
thanks in advanced.
Given that you're not using game, game_actions, or emails for any purpose (they're not filtering users, and you're not enriching the results with data from either of these tables), there's no need to join those tables at all:
SELECT
u.*
FROM users u
WHERE u.user_id = 0
AND u.is_contact_by_email = 1
You may group result by user_id and use aggregate functions to return other fields, for eaxmple -
SELECT u.user_id, GROUP_CONCAT(g.game_id) games FROM users u
LEFT JOIN game g
ON g.user_id = u.user_id
LEFT JOIN game_actions ga
ON ga.game_id = g.id
LEFT JOIN emails e
ON e.id = ga.email_id
WHERE
u.user_id = 0 AND u.is_contact_by_email = 1
GROUP BY
u.user_id
I suppose there are more games, actions, and emails for each user. How do you imagine the result table to look like? Because when you are selecting only from user table (SELECT u.*), then there is no point in joining others. If you need the other tables, use GROUP BY (u.user_id) to group rows by user.
Try to use keyword distinct with your query
Been coding for 48 hours straight and am banging my head against the wall here. Please help me with this small issue.
My SQL query is this:
SELECT u.Firstname, u.Lastname, u.Rep, u.Email, u.Password, u.Gender, u.Level,
u.Birthday, u.Achievements, u.Height, u.Unit, u.cityid, u.countryid,
r.RegDate, ci.Name AS City, co.Name AS Country
FROM Users u, Registry r, Cities ci, Countries co
WHERE u.id = 1 AND r.uid = u.id AND u.cityid = ci.id AND u.countryid = co.id
LIMIT 1
My problem is that I just noticed that sometimes Users.cityid and Users.countryid are NULL (which is OK).
I want the query to give me all the other info (like, return NULL for City and Country) for this user even if one or both those fields are NULL. How to make the AND-parts conditional?
I hope I'm making myself clear in my fogginess.
I think you need a couple of OUTER joins if I have understood your situation correctly.
SELECT ...
FROM Users u
INNER JOIN Registry r ON r.uid = u.id
LEFT JOIN Cities ci ON u.cityid = ci.id
LEFT JOIN Countries co ON u.countryid = co.id
WHERE u.id = 1
You need to use a LEFT JOIN on your tables instead of using a WHERE.
So your FROM turns into:
FROM Users u JOIN Registry r on u.id = r.uid
LEFT JOIN Cities ci ON u.cityid = ci.id
LEFT JOIN Countries co ON u.countryid = co.id
WHERE u.id = 1 LIMIT 1
The LEFT JOIN is an OUTER join; it will join across the tables where the leftmost (hence the LEFT in the JOIN) term in the JOIN (i.e., the first one that appears) has an entry but the other table does not. OUTER JOINs are useful for these situations where you don't necessarily have data entries in all the tables for what you want from a query; they can be confusing at first, but they become very important to using SQL well.