So, I am trying to select some data from 4 tables using a query I have attempted to throw together.
SELECT *
FROM cards
LEFT JOIN cards_viewers ON cards.card_id = cards_viewers.card_id
(SELECT *
FROM folders
WHERE folder_id = cards.card_folderID)
(SELECT user_firstName,
user_lastName,
user_avatar
FROM user_data
WHERE user_id = cards_viewers.user_id)
WHERE cards_viewers.user_id = '.$u_id.'
ORDER BY cards.card_lastUpdated DESC
Basically, the query selects data from the four tables depending on the user_id in table user_data. I have attempted to initially fetch all data from the tables cards, and cards_viewers, and have went on to use this data to select values from the other tables (user_data and folders).
The query is wrong, I know that. I have learnt the majority of basic MySQL, but I am still struggling with more complex queries like the one I am trying to write now. What query can I use to select the data I want?
Links to any documentation to parts of queries would prove very useful in helping me learn how to create queries in future, rather than just relying on StackOverflow.
Many thanks.
You don't need "MULTI-WHERE" but multiple joins, you just need to keep doing joins until you get the tables you need.
Here's an example:
SELECT *
FROM cards LEFT JOIN cards_viewers
ON cards.card_id = cards_viewers.card_id
LEFT JOIN folders
ON folders.folder_id = cards.card_folderID
LEFT JOIN user_data
ON user_id = cards_viewers.user_id
WHERE cards_viewers.user_id = '.$u_id.'
ORDER BY cards.card_lastUpdated DESC
To custom the fields you want to get just change * for the name of the field being careful about ambiguous column naming.
For further information check MySql Joins. Hope this helped you :)
Related
I have a MySQL database that has three tables holding information about uploaded photos by users. I have a PHP page that displays all the photos in the database (tbl_uploads) and who uploaded them (tbl_users). To display the photos and who uploaded them I have a join in the MySQL query.
SELECT *
FROM tbl_uploads, tbl_users
WHERE tbl_uploads.user_id = tbl_users.user_id
ORDER BY date DESC
I now want to join a third table tbl_collab to the MySQL query that allows me to display all the users that collaborated with the photo (a form allows them to post the $file and their $user_id to tbl_collab). I guess I need to add a join from tbl_uploads.file with tbl_collab.user_id but I'm not sure how.
tbl_users
|//**user_id**//|int(11)|No|
|user_name|varchar(25)|No|
|user_email|varchar(60)|No|
|user_password|varchar(255)|No|
|joining_date|datetime|No|
tbl_uploads
|//**id**//|int(10)|No|
|file|varchar(100)|No|
|type|varchar(30)|No|
|size|int(11)|No|
|user_id|int(11)|No|
|user_name|varchar(25)|No|
tbl_collab
|//**id**//|int(11)|No|
|user_name|varchar(100)|No|
|user_id|int(11)|No|
|file|varchar(255)|No|
I have been trying your various suggestions and I can't really get them to work as I would hope so I have made a mysql fiddle that might be help me.
The problem is that when I loop through the rows that the query throws up in PHP I ether get just the rows where there is join with tbl_uploads.file and tbl.collab.file or I get the multiple rows duplicating themselves.
I'd suggest preferring ANSI SQL syntax for joins (over mentioning multiple tables in the "from" clause) as once the queries get complex I find the ANSI syntax easier to follow. Using that syntax, joining multiple tables is no big deal. e.g.,
SELECT uploads.<column>, users.<column>, collabs.<column>
FROM tbl_uploads uploads
JOIN tbl_users users ON users.user_id=uploads.user_id
JOIN tbl_collabs collabs ON collabs.file=uploads.file
ORDER BY uploads.date DESC
(Note, replace <column> above with the names of columns you want to select from the respective tables, using AS syntax to provide unique names where necessary.)
Consider that you will probably want to create indexes over the fields in the join conditions for performance if you expect the database will become large. You may also want to use left joins when joining, e.g., tbl_collabs if it is possible an upload will have no collaborators, otherwise the query will return no data if there are no matching rows in tbl_collabs.
The first thing to do is to normalize your data. If you look closely, username appears in all three tables. It shouldn't. It belongs only in the users table. Then your other tables need to have a user_id field instead of the username.
tbl_uploads
|//**id**//|int(10)|No|
|file|varchar(100)|No|
|type|varchar(30)|No|
|size|int(11)|No|
|user_id|int(11)|No|
tbl_collab
|//**id**//|int(11)|No|
|user_id|int(11)|No|
|file|varchar(255)|No|
In both cases the user_id is a foreign key to the id field in the users table. Now we have something consistent to join on.
SELECT * FROM tbl_uploads
INNER JOIN tbl_users ON tbl_uploads.user_id = tbl_users.user_id
INNER JOIN tbl_collab ON tbl_collab.file = tbl_uploads.file
Whether you should use INNER JOIN or LEFT JOIN depends on exactly what you need to do with your data, but INNER JOIN seems more appropriate based on information provided.
Update: As #drew pointed out, none of your tables have a column named date did you perhaps intend to sort by tbl_users.joining_date?
Seems the join is on file to me
SELECT *
FROM tbl_uploads
inner join tbl_users on tbl_uploads.user_id = tbl_users.user_id
inner join tbl_collab on tbl_collab.file = tbl_uploads.file
ORDER BY date DESC
You can just add another join condition. Also, note that implicit joins (having multiple tables in the from clause) isn't considered a good practice, and you should probably use explicit join clauses:
SELECT *
FROM tbl_uploads up
JOIN tbl_users us ON up.user_id = us.user_id
JOIN tbl_collab c ON c.user_id = up.user_id
ORDER BY date DESC
I'm facing a problem here:
I'm building a forum, this forum has several tables and I'm trying to fetch the comments and user info in a single query.
So far, it should be easy, the problem is that I can't change the structure and with the following query I get a perfect result IF there is a like to the answer. If no one likes the answer it fails.
Select
mfr.mfr_forum_answers.id,
mfr.mfr_forum_answers.date_created,
mfr.mfr_forum_answers.last_updated,
mfr.mfr_forum_answers.content,
mfr.mfr_forum_answers.accepted,
mfr.mfr_forum_answers.user_id,
mfr.mfr_users.level,
mfr.mfr_users.avatar,
mfr.mfr_forum_likes.subject_id,
mfr.wp_users.ID As ID1,
mfr.mfr_forum_topics.user_id As owner_id,
(SELECT count(mfr.mfr_forum_likes.id) FROM mfr.mfr_forum_likes WHERE mfr.mfr_forum_likes.subject_id = :id AND mfr.mfr_forum_likes.type = 'answer') as likes,
(SELECT count(mfr.mfr_forum_likes.id) FROM mfr.mfr_forum_likes WHERE mfr.mfr_forum_likes.subject_id = :id AND makefitreal.mfr_forum_likes.type = 'answer' AND mfr.mfr_forum_likes.user_id = :sessionId ) as i_like,
mfr.wp_users.user_nicename
From
mfr.mfr_forum_likes Inner Join
mfr.mfr_forum_answers
On mfr.mfr_forum_answers.topic_id =
mfr.mfr_forum_likes.subject_id Inner Join
mfr.mfr_users
On mfr.mfr_forum_answers.user_id = mfr.mfr_users.id
Inner Join
mfr.wp_users
On mfr.mfr_users.id = mfr.wp_users.ID Inner Join
mfr.mfr_forum_topics
On mfr.mfr_forum_answers.topic_id = mfr.mfr_forum_topics.id
Where
mfr.mfr_forum_answers.topic_id = :id
And
mfr.mfr_forum_likes.type = 'answer'
So far as said it returns only if an answer has a like, I'm thinking on adding a add to the user who posts the answer by default but I'm trying to improve my skills by solving new issues.
If someone has a suggestion in how I could overcome the fact that if a table is empty, the query continues I'd be really thankfull.
Thanks in advance-
Pihh
Yes. What you are looking for are called left and right joins. According to the documentation, with a LEFT JOIN you still join two tables as normal but
If there is no matching row for the right table in the ON or USING part in a LEFT JOIN, a row with all columns set to NULL is used for the right table.
This means that you can try to join two tables, but if a row does not have any results it will still return the results from the first table. The same is true for a RIGHT JOIN only it works the opposite way: it will return results if the tabled being joined to has results, but the original table does not.
It looks like you have 3 tables for 3 relationships: there are answers, a user gives an answer, and an answer might or might not have like. To grab this data, I would suggest starting from your answers table, performing an INNER JOIN on your users table (assuming there are always users), and a LEFT JOIN on your likes table. Here is a simple example:
SELECT *
FROM answers
INNER JOIN users ON users.id = answers.user_id
LEFT JOIN likes ON likes.answer_id = answer.id
WHERE answers.id = :id
AND likes.type = 'answers'
Of course, if for some unknown reason you need to start from your likes table, then you'd have to RIGHT JOIN the other tables. I hope that gives you a good idea of how you'd make your query.
I am having 3 tables (c19 , c19b2, g26) in a database
I want to write a SQL Query to search and display all fields of the matched record.
I am using following query:
$query = "SELECT * FROM c19,c19b2,g26 WHERE armyno LIKE '%$searchTerm%'";
But it only works for table c19,
Data from the other 2 tables is not fetched.Each table has a field armyno
Please help me with this
Thank you.
Alright, you are not looking for a JOIN, but a UNION.
SELECT * FROM c19 WHERE armyno LIKE '%$searchTerm%'
UNION
SELECT * FROM c19b2 WHERE armyno LIKE '%$searchTerm%'
UNION
SELECT * FROM g26 WHERE armyno LIKE '%$searchTerm%'
That will let you query all three tables at the same time.
Which DB are you using? This would have worked in SQL Server. However, notice you are doing a cross join of every record to every record... usually you only want to match some records by restriction of a matching key, for example:
select
*
from a
left join b on b.somekey = a.somekey
left join c on c.someotherkey = b.someotherkey
In SQL server you can just say *, but I'm taking it that in your DB engine that didn't work, so try specifying which table. This may in some environments require aliasing as well:
select
a.*,
b.*,
c.*
from tableA as a
left join tableB as b on b.somekey = a.somekey
left join tableC as c on c.someotherkey = b.someotherkey
Generally, you should see the columns from the first table, followed by the columns from the second table, followed by columns from the third table for a given row. If you wanted to get all columns from all tables, but separately, then that would be 3 separate selects.
Lastly, if all 3 tables have "armyno" then I'd expect it to throw an ambiguous field error. In such case you'd want to specify which table's "armyno" field to filter on.
I am trying to query two tables: finished_events and flagged_events. 1st of all I need everything related to the company_id so
SELECT *
FROM finished_events
WHERE company_id=$id
ORDER by schedule, timestamp
I then changed this to:
SELECT * FROM finished_events
INNER JOIN flagged_events
ON finished_events.company_id=flagged_events.company_id
WHERE finished_events.company_id=$id
ORDER by finished_events.schedule, finished_events.timestamp
I have tried using FULL JOIN, LEFT JOIN, and RIGHT JOINs all unsuccessful. Specifically what I want is to get is a combined effort of the following code:
$sql = "SELECT *
FROM finished_events
WHERE company_id=$id
ORDER by schedule, time_stamp";
$flagged_sql = "SELECT *
FROM flagged_events
WHERE company_id=$id
ORDER by schedule, time_stamp";
The tables are a bit different so UNION won't work here. I can post dummy database entries but this won't be of too much help as I need all from both tables. The 2 links between the tables would be the company_id and the schedule columns. Essentially what is going on behind the scenes is timestamps being put into a different table to which I then process either into finished_events or flagged_events. Flagged events will need the user to do something about it until it is a finished event. So this script is generating the data for the GUI, hence why I need to query both tables and create an associative array of customer details then an array of events (from these 2 tables). So creating the assoc_array is no problem I just need to get this query to spit out all the events and order them correctly. Let me know if you need anything specific to solve this one, thanks :)
EDIT
SQL Fiddle: http://sqlfiddle.com/#!2/d4c30/1
this almost fixes it but not quite right, it repeats entries at the bottom
If I understood correctly, this may be useful for you:
SELECT a.* FROM (
SELECT *, 'finished' as event_type FROM finished_events
UNION
SELECT *, 'flagged' as event_type FROM flagged_events) a
ORDER BY a.schedule, a.time_stamp
I'm having trouble with a join query, my issue is as follows.
Table: battles
Fields: id,attacker_id,defender_id
Table: users
Fields: id,profile_image
I would like to do a query to retrieve a battle and get the profile images as well from the other table.
Is there a way to do this in a single or do I have to do more than one?
Thanks in advance.
I wanted to wait a while to see if you had any attempt or if you will answer my first question to know if I understood the problem. But maybe you don't have a starting point. Try something like:
SELECT
a.profile_image as attacker_profile_image,
d.profile_image as defender_profile_image
FROM
`battles` b
LEFT JOIN
`users` a
ON
b.`attacker_id` = a.`id`
LEFT JOIN
`users` d
ON
b.`defender_id` = d.`id`
the problem here is the fact that you need to join with the users table twice, so you will need to create aliases for the columns you plan to use
This query will fetch the two images only, you will need to add the extra fields