I have two table:
Site:
id | name
1 | google
2 | stackoverflow
3 | cnn.com
Confirm:
id | site_id | type // (type = 1, 2 or 3)
1 | 1 | 2
2 | 2 | 1
so and would like get Sites which is not added to table Confirm with type for example 1.
SELECT *
FROM Site
LEFT JOIN Confirm
ON Site.id = Confirm.site_id
and what next?
A natural way to write this query is as a NOT EXISTS query:
SELECT s.*
FROM Sites s
WHERE NOT EXISTS (SELECT 1 FROM Confirm c WHERE c.site_id = s.id AND type = 1);
It is almost a 1-1 translation of the problem statement: "would like to get sites that are not added to Confirm with type = 1".
I do not understand what you meant. But if you are in doubt about how to work with result sets from the database, look at this, maybe it can help you: http://www.codeproject.com/KB/database/Visual_SQL_Joins/Visual_SQL_JOINS_orig.jpg
Related
I am making a web dating app that needs to match users and let them chat with each other.
I want to figure out how to find all the matches for a particular user.
Right now I have a table called follows that has 2 columns.
UserID | MatchUserID
--------------------
1 | 2
2 | 1
1 | 3
1 | 4
1 | 5
4 | 1
5 | 4
The idea is that for two users to match they need to follow one another. The table above shows which user follows which.
Assuming that the user who is currently logged on is UserID = 1.
I need a query that will return from the MatchUserID table the following results:
2, 4
In a way, I am looking to find all the opposite combinations between the two columns.
This is the code I use to create the table.
CREATE TABLE Match
(
UserID INT NOT NULL,
MatchUserID INT NOT NULL,
PRIMARY KEY (UserID, MatchUserID)
);
You can do it with a self join:
select m.MatchUserID
from `Match` m inner join `Match` mm
on mm.MatchUserID = m.UserId
where
m.UserId = 1
and
m.MatchUserID = mm.UserId
See the demo.
Results:
| MatchUserID |
| ----------- |
| 2 |
| 4 |
The simplest way possibly is to use EXISTS and a correlated subquery that searches for the other match.
SELECT t1.matchuserid
FROM elbat t1
WHERE t1.userid = 1
AND EXISTS (SELECT *
FROM elbat t2
WHERE t2.matchuserid = t1.userid
AND t2.userid = t1.matchuserid);
I have two tables, one is an index (or map) which helps when other when pulling queries.
SELECT v.*
FROM smv_ v
WHERE (SELECT p.network
FROM providers p
WHERE p.provider_id = v.provider_id) = 'RUU='
AND (SELECT p.va
FROM providers p
WHERE p.provider_id = v.provider_id) = 'MjU='
LIMIT 1;
Because we do not know the name of the column that holds the main data, we need to look it up, using the provider_id which is in both tables, and then query.
I am not getting any errors, but also no data back. I have spent the past hour trying to put this on sqlfiddle, but it kept crashing, so I just wanted to check if my code is really wrong, hence the crashing?
In the above example, I am looking in the providers table for column network, where the provider_id matches, and then use that as the column on smv.
I am sure i have done this before just like this, but after the weekend trying I thought i would ask on here.
Thanks in Advance.
UPDATE
Here is an example of the data:
THis is the providers, this links so no matter what the name of the column on the smv table, we can link them.
+---+---+---------------+---------+-------+--------+-----+-------+--------+
| | A | B | C | D | E | F | G | H |
+---+---+---------------+---------+-------+--------+-----+-------+--------+
| 1 | 1 | Home | network | batch | bs | bp | va | bex |
| 2 | 2 | Recharge | code | id | serial | pin | value | expire |
+---+---+---------------+---------+-------+--------+-----+-------+--------+
In the example above, G will mean in the smv column for recharge we be value. So that is what we would look for in our WHERE clause.
Here is the smv table:
+---+---+-----------+-----------+---+----+---------------------+-----+--+
| | A | B | C | D | E | F | value | va |
+---+---+-----------+-----------+---+----+---------------------+-----+--+
| 1 | 1 | X2 | Home | 4 | 10 | 2016-09-26 15:20:58 | | 7 |
| 2 | 2 | X2 | Recharge | 4 | 11 | 2016-09-26 15:20:58 | 9 | |
+---+---+-----------+-----------+---+----+---------------------+-----+--+
value in the same example as above would be 9, or 'RUU=' decoded.
So we do not know the name of the rows, until the row from smv is called, once we have this, we can look up what column name we need to get the correct information.
Hope this helps.
MORE INFO
At the point of triggering, we do not know what the row consists of the right data because some many of the fields would be empty. The map is there to help we query the right column, to get the right row (smv grows over time depending on whats uploaded.)
1) SELECT p.va FROM providers p WHERE p.network = 'Recharge' ;
2) SELECT s.* FROM smv s, providers p WHERE p.network = 'Recharge';
1) gives me the correct column I need to look up and query smv, using the above examples it would come back with "value". So I need to now look up, within the smv table, C = Recharge, and value = '9'. This should bring me back row 2 of the smv table.
So individually both 1 and 2 queries work, but I need them put together so the query is done on the database server.
Hope this gives more insight
Even More Info
From reading other posts, which are not really doing what I need, i have come up with this:
SELECT s.*
FROM (SELECT
(SELECT p.va
FROM dh_smv_providers p
WHERE p.provider_name = 'vodaphone'
LIMIT 1) AS net,
(SELECT p.bex
FROM dh_smv_providers p
WHERE p.provider_name = 'vodaphone'
LIMIT 1) AS bex
FROM dh_smv_providers) AS val, dh_smv_ s
WHERE s.provider_id = 'vodaphone' AND net = '20'
ORDER BY from_base64(val.bex) DESC;
The above comes back blank, but if i replace net, in the WHERE clause with a column I know exists, I do get the results expected:
SELECT s.*
FROM (SELECT
(SELECT p.va
FROM dh_smv_providers p
WHERE p.provider_name = 'vodaphone'
LIMIT 1) AS net,
(SELECT p.bex
FROM dh_smv_providers p
WHERE p.provider_name = 'vodaphone'
LIMIT 1) AS bex
FROM dh_smv_providers) AS val, dh_smv_ s
WHERE s.provider_id = 'vodaphone' AND value = '20'
ORDER BY from_base64(val.bex) DESC;
So what I am doing wrong, which is net, not showing the value derived from the subquery "value" ?
Thanks
SELECT
v.*,
p.network, p.va
FROM
smv_ v
INNER JOIN
providers p ON p.provider_id = v.provider_id
WHERE
p.network = 'RUU=' AND p.va = 'MjU='
LIMIT 1;
The tables talk to each other via the JOIN syntax. This completely circumvents the need (and limitations) of sub-selects.
The INNER JOIN means that only fully successful matches are returned, you may need to adjust this type of join for your situation but the SQL will return a row of all v columns where p.va = MjU and p.network = RUU and p.provider_id = v.provider_id.
What I was trying to explain in comments is that subqueries do not have any knowledge of their outer query:
SELECT *
FROM a
WHERE (SELECT * FROM b WHERE a)
AND (SELECT * FROM c WHERE a OR b)
This layout (as you have in your question) is that b knows nothing about a because the b query is executed first, then the c query, then finally the a query. So your original query is looking for WHERE p.provider_id = v.provider_id but v has not yet been defined so the result is false.
I'm having 2 tables. Table A contains a list of people who booked for an event, table B has a list of people the booker from table A brings with him/her. Both tables have many colums with unique data that I need to do certain calculations on in PHP , and as of now I do so by doing queries on the tables with a recursive PHP function to resolve it. I want to simplify the PHP and reduce the amount of queries that come from this recursive function by doing better MYSQL queries but I'm kind of stuck.
Because the table has way to many columns I will give an Excerpt of table A instead:
booking_id | A_customer | A_insurance
1 | 134 | 4
Excerpt of table B:
id | booking_id | B_insurance
1 | 1 | 0
2 | 1 | 1
3 | 1 | 1
4 | 1 | 3
The booking_id in table A is unique and set to auto increment, the booking_id in table b can occur many times (depending on how many guests the client from table A brings with him). Lets say I want to know every selected insurance from customer 134 and his guests, then I want the output like this:
booking_id | insurance
1 | 4
1 | 0
1 | 1
1 | 1
1 | 3
I have tried a couple of joins and this is the closest I've came yet, unfortunately this fails to show the row from A and only shows the matching rows in B.
SELECT a.booking_id,a.A_customer,a.A_insurance,b.booking_id,b.insurance FROM b INNER JOIN a ON (b.booking_id = a.booking_id) WHERE a.booking_id = 134
Can someone point me into the right direction ?
Please note: I have altered the table and column names for stackoverflow so it's easy for you guys to read, so it's possible that there is a typo that would break the query in it right now.
I think you need a union all for this:
select a.booking_id, a.insurance
from a
where a.a_customer = 134
union all
select b.booking_id, b.insurance
from a join
b
on a.booking_id = b.booking_id
where a.a_customer = 134;
The simplest way I can think of to achieve this is to use a UNION:
SELECT booking_id, A_insurance insurance
FROM A
WHERE booking_id = 134
UNION
SELECT booking_id, B_insurance insurance
FROM B
WHERE booking_id = 134
As my understanging of your isso is right, that should give you the result you need:
SELECT a.booking_id,a.insurance FROM a WHERE a.booking_id = 134
union
SELECT a.booking_id,b.insurance FROM b INNER JOIN a ON (b.booking_id = a.booking_id) WHERE a.booking_id = 134
I currently have a web app where users can share posts and connect with other users. I store each post in a table named "posts" and all of the relationships between users in a table called "relations"
The structure of "posts" is:
+-------------+-----------+---------+------------+----------------+
| post_id | user_id | text | date | privacy |
+-------------+-----------+---------+------------+----------------+
| 1 | 4 | Hello | 1/13/2014 | 2 |
+-------------+-----------+---------+------------+----------------+
Privacy can either be 1 or 2
The structure of "relations" is:
+-------------+-----------+------------+------------+
|rel_id | sender | recipient | status |
+-------------+-----------+------------+------------+
| 1 | 17 | 4 | 1 |
+-------------+-----------+------------+------------+
Status can either be 1 or 2
Now, I want to have a "News Feed" like page where the user can see all of the posts from the people they are either friends with (status= 2) or following (status= 1). But I am having trouble with the query. I know how to do simple select queries, but I don't think that is possible with this.
So, I would like to select all of the posts from the "posts" table where the 'user_id' is the same as 'recipient' in the "relations" table where also the sender equals '17' (I am going to use a variable). Now on top of that, if the status of that row from "relations" is '1' and the 'privacy' from the "posts" row is '2', then skip that post.
How would I write this query?
Use joins
SELECT * FROM `posts`
join `relations` on `recipient` = `user_id`
WHERE `status` = 2
Use joins and where clauses, as follows:
SELECT *
FROM posts p
JOIN relations r ON p.user_id = r.recipient
WHERE (r.status = 1 OR r.status = 2)
AND (r.status != 1 OR p.privacy != 2);
For succinctness, it helps to alias the tables (eg "posts p") so that you can subsequently refer to fields from each of them specifically (eg "p.privacy").
This will join the tables, including any where relations.status is 1 or 2, yet skipping any where both relations.status is 1 and posts.privacy is 2.
Here is the question
we have 3 database variable(Person, event,invited)
Person(pid,passwd,fname,lname),
Event(eid, start_time,duration,description,pid)
Invited(pid,eid,response,visibility)
I want to make a query witch will do
show all people each event user X create.
For example Person David create the event with eid= 1 and 3. (2events)
and if Jany and Will invited to the eid =1 , and Mike invited to event 3
it should show
EID PID
1 Jany
1 will
3 mike
The part I confused is Person and Event 's PID is a creater of the event
and invited's PID is for person who invited. so its different PID value.
so i can not just natural join them
I can solve this problem with create view mysql command but I'm writing this code
on PHP form so I want to finish this command in one command.
what i tried is this
select *
from invited
where eid
in (SELECT eid
from person natural join event
where pid = 'DD')
But it does not give what I expected.
How to write the code in One command without 'create view' command for this problem?
Are you looking for this?
SELECT e.eid, i.pid, p.fname
FROM event e JOIN invited i
ON e.eid = i.eid JOIN person p
ON i.pid = p.pid
WHERE e.pid = ?
Sample output:
| EID | PID | FNAME |
|-----|-----|-------|
| 1 | 2 | Jany |
| 1 | 3 | Will |
| 3 | 4 | Mike |
Here is SQLFiddle demo
Recommended reading
A Visual Explanation of SQL Joins