i need help in select sql statement.
in my mysql database:
location table
serialID(AI)|locations | telephone | address
---------------------------------------------
1 | A
2 | B
3 | C
4 | D
users table
userID | location chosen
-------------------------
1 | A
2 | B
3 | B
I want to count the number of people who choose a particular location and display in the table. So if this particular location have more users choosen as their favourite location, it will move up to the first row. May I know how can I do this?
something like this when it populate into dynamic table ->
location | address | telephone | user's favourable
B | - | - | 2
A | - | - | 1
C | - | - | 0
D | - | - | 0
You could just do a query like this:
SELECT l.locations, l.telephone, l.address, COUNT (u.userID) as `location_count`
FROM location AS l
LEFT OUTER JOIN users AS u on l.locations = u.location_chosen
GROUP BY l.locations
ORDER BY `location_count` DESC
Try something like this:
SELECT l.location, l.address, l.telephone, COUNT(u.userID) AS [users favourable]
FROM location l
LEFT JOIN
users u
ON l.location = u.locationchosen
GROUP BY l.location, l.address, l.telephone
SELECT loc.*, countResult.usersFavourable
FROM location loc
LEFT JOIN
(
SELECT locationChoosen, COUNT(*) `usersFavourable`
FROM users
GROUP BY locationChoosen
) countResult ON loc.locations = countResult.locationChoosen
ORDER BY countResult.usersFavourable DESC, loc.locations
use this:
select count(userId) count,locations,address,telephone
from Table1 Left join Table2
on Table1.locations = Table2.location
group by locations order by count desc ;
see here.. link
SELECT LocationChosen, Count(*) FROM usersTable GROUP BY LocationChosen
Related
I've been trying for two days, without luck.
I have the following simplified tables in my database:
customers:
| id | name |
| 1 | andrea |
| 2 | marco |
| 3 | giovanni |
access:
| id | name_id | date |
| 1 | 1 | 5000 |
| 2 | 1 | 4000 |
| 3 | 2 | 1500 |
| 4 | 2 | 3000 |
| 5 | 2 | 1000 |
| 6 | 3 | 6000 |
| 7 | 3 | 2000 |
I want to return all the names with their last access date.
At first I tried simply with
SELECT * FROM customers LEFT JOIN access ON customers.id =
access.name_id
But I got 7 rows instead of 3 as expected. So I understood I need to use GROUP BY statemet as the following:
SELECT * FROM customers LEFT JOIN access ON customers.id =
access.name_id GROUP BY customers.id
As far I know, GROUP BY combines using a random row. In fact I got unordered access dates with several tests.
Instead I need to group every customer id with its corresponding latest access! How this can be done?
You have to get the latest date from the access table with a group by on the the name_id, then join this result with the customer table. Here is the query:
select c.id, c.name, a.last_access_date from customers c left join
(select id, name_id, max(access_date) last_access_date from access group by name_id) a
on c.id=a.name_id;
Here is a DEMO on sqlfiddle.
I think this is what you'd like to achieve:
SELECT c.id, c.name, max(a.date) last_access
FROM customers c
LEFT JOIN access a ON c.id = a.name_id
GROUP BY c.id, c.name
The LEFT join will return all entries in table customers regardless if the join criteria (c.id = a.name_id) is satisfied. This means that you might get some NULL entries.
Example:
Simply add a new row in the customers table (id: 4, name: manuela). The output will have 4 rows and the newest row will be (id: 4, last_access: null)
I would do this using a correlated subquery in the ON clause:
SELECT a.*, c.*
FROM customers c LEFT JOIN
access a
ON c.id = a.name_id AND
a.DATE = (SELECT MAX(a2.date) FROM access a2 WHERE a2.name_id = a.name_id);
If this statement is true:
I need to group every customer id with its corresponding latest access! How this can be done?
Then you can simply do:
select a.name_id, max(a2.date)
from access a
group by a.name_id;
You do not need the customers table because:
All customers are in access, so the left join is not necessary.
You need no columns from customers.
I'm stuck on a rather complex query.
I'm looking to write a query that shows the "top five customers" as well as some key metrics (counts with conditions) about each of those customers. Each of the different metrics uses a totally different join structure.
+-----------+------------+ +-----------+------------+ +-----------+------------+
| customer | | | metricn | | | metricn_lineitem |
+-----------+------------+ +-----------+------------+ +-----------+------------+
| id | Name | | id | customer_id| |id |metricn_id |
| 1 | Customer1 | | 1 | 1 | | 1 | 1 |
| 2 | Customer2 | | 2 | 2 | | 2 | 1 |
+-----------+------------+ +-----------+------------+ +-----------+------------+
The issue this is that I always want to group by this customer table.
I first tried to put all of my joins into the original query, but the query was abysmal with performance. I then tried using subqueries, but I couldn't get them to group by the original hospital id.
Here's a sample query
SELECT
customer.name,
(SELECT COUNT(metric1_lineitem.id)
FROM metric1 INNER JOIN metric1_lineitem
ON metric1_lineitem.metric1_id = metric1.id
WHERE metric1.customer_id = customer_id
) as metric_1,
(SELECT COUNT(metric2_lineitem.id)
FROM metric2 INNER JOIN metric2_lineitem
ON metric2_lineitem.metric2_id = metric2.id
WHERE metric2.customer_id = customer_id
) as metric_2
FROM customer
GROUP BY customer.name
SORT BY COUNT(metric1.id) DESC
LIMIT 5
Any advice? Thanks!
SELECT name, metric_1, metric_2
FROM customer AS c
LEFT JOIN (SELECT customer_id, COUNT(*) AS metric_1
FROM metric1 AS m
INNER JOIN metric1_lineitem AS l ON m.id = l.metric1_id
GROUP BY customer_id) m1
ON m1.customer_id = c.customer_id
LEFT JOIN (SELECT customer_id, COUNT(*) AS metric_2
FROM metric2 AS m
INNER JOIN metric2_lineitem AS l ON m.id = l.metric2_id
GROUP BY customer_id) m1
ON m2.customer_id = c.customer_id
ORDER BY metric_1 DESC
LIMIT 5
You should also avoid using COUNT(columnname) when you can use COUNT(*) instead. The former has to test every value to see if it's null.
Although your data structure may be lousy, your query may not be so bad, with two exceptions. I don't think you need the aggregation on the outer level. Also, the "correlation"s in the where clause (such as metric1.customer_id = customer_id) are not doing anything, because customer_id is coming from the local tables. You need metric1.customer_id = c.customer_id:
SELECT c.name,
(SELECT COUNT(metric1_lineitem.id)
FROM metric1 INNER JOIN
metric1_lineitem
ON metric1_lineitem.metric1_id = metric1.id
WHERE metric1.customer_id = c.customer_id
) as metric_1,
(SELECT COUNT(metric2_lineitem.id)
FROM metric2 INNER JOIN
metric2_lineitem
ON metric2_lineitem.metric2_id = metric2.id
WHERE metric2.customer_id = c.customer_id
) as metric_2
FROM customer c
ORDER BY 1 DESC
LIMIT 5;
How can you make this run faster? One way is to introduce indexes. I would recommend metric1(customer_id), metric2(customer_id), metric1_lineitem(metric1_id) and metric2_lineitem(metric2_id).
This may be faster than the aggregation method (proposed by Barmar) because MySQL is inefficient with aggregations. This should allow the aggregations to take place only using indexes instead of the base tables.
I have 2 tables that look like this:
users (uid, name)
-------------------
| 1 | User 1 |
| 2 | User 2 |
| 3 | User 3 |
| 4 | User 4 |
| 5 | User 5 |
-------------------
highscores (user_id, time)
-------------------
| 3 | 12005 |
| 3 | 29505 |
| 3 | 17505 |
| 5 | 19505 |
-------------------
I want to query only for users that have a highscore and only the top highscore of each user. The result should look like:
------------------------
| User 3 | 29505 |
| User 5 | 19505 |
------------------------
My query looks like this:
SELECT user.name, highscores.time
FROM user
INNER JOIN highscores ON user.uid = highscores.user_id
ORDER BY time ASC
LIMIT 0 , 10
Actually this returns multiple highscores of the same user. I also tried to group them but it did not work since it did not return the best result but a random one (eg: for user id 3 it returned 17505 instead of 29505).
Many thanks!
You should use the aggregated function MAX() together with group by clause.
SELECT a.name, MAX(b.`time`) maxTime
FROM users a
INNER JOIN highscores b
on a.uid = b.user_id
GROUP BY a.name
SQLFiddle Demo
Your effort of grouping users was correct. You just needed to use MAX(time) aggregate function instead of selecting only time.
I think you wrote older query was like this:
SELECT name, time
FROM users
INNER JOIN highscores ON users.uid = highscores.user_id
GROUP BY name,time
But actual query should be:
SELECT user.name, MAX(`time`) AS topScore
FROM users
INNER JOIN highscores ON users.uid = highscores.user_id
GROUP BY user.name
I have an implementation messages system.
My problem is, I would like to know whether a user already has a thread with another user and if so what is the mid
I have a messages_recips table which look like this
---------------------------
| mid | seq | uid | status|
|--------------------------
| 4 | 1 | 1 | A |
| 4 | 1 | 2 | A |
---------------------------
if user id 1 having a thread with user id 2 I hold 2 rows with same mid.
I know I can create 2 sqls to achieve what I'm asking for, but I'm trying to do it in 1 sql.
As noted by Waqar Janjua, the key to this is a self-join query:
SELECT m1.mid
FROM messages_recips AS m1
JOIN messages_recips AS m2 ON m1.mid = m2.mid
WHERE m1.uid = 1
AND m2.uid = 2
I think you have to write a self-join query:
Select u.uid, u1.uid from tablename u
INNER JOIN tablename u1 on u.mid = u1.mid
You will get all the users who have the same mid.
In order to get only user1 and user2 records you have to place a where clause at the end of the query lik this.
Select u.uid, u1.uid from tablename u
INNER JOIN tablename u1 on u.mid = u1.mid
Where ( u.uid In ( 1,2 ) OR u1.uid In ( 1,2 ) ) ;
I have 2 tables in my database that look like so:
clients
+-------------+
| id | sms |
|------+------|
| 1 | 0 |
| 2 | 1 |
| 3 | 1 |
| 4 | 1 |
+------+------+
clients_lists_relationships
+----------------------+
| listid | clientid |
|----------+-----------|
| 1 | 1 |
| 1 | 2 |
| 2 | 1 |
| 3 | 1 |
+----------+-----------+
Now what I'm trying to do is get a list of clients who are in a bunch of lists. I do that like so:
SELECT c.id,
l.*
FROM clients AS c,
clients_lists_relationships AS l
WHERE c.id = l.clientid
AND c.sms = '1'
AND ( l.listid = '1'
OR l.listid = '2' );
This does give me a list of the clients that I need. But because a client can be in more than one list I get the same client more than once. How would I limit this to only one row for each client no matter how many lists they are in?
If you just need any client that is in a list, you can just query the relationship table:
SELECT DSITINCT(clientid) FROM clients_lists_relationships
You can also use that distinct on your combined query, but be aware that the "listid" you'll get is just one.
Use GROUP BY:
SELECT c.id,
l.listid
FROM clients c
INNER JOIN clients_lists_relationships l
ON c.id = l.clientid
WHERE c.sms = 1
AND l.listid IN (1,2)
GROUP BY c.id
Note that by doing this you lose information on which lists the client was a member of. This means that you should probably not select anything from client_lists_relationships as this information is either redundant (clientid) or incomplete (listid).
First of all take a look at MySQL:: JOIN It's much better than the WHERE statements you use now.
I think you are looking for GROUP BY.
In total, the query look like:
SELECT
c.id,
l.*
FROM
clients AS c
INNER JOIN
clients_lists_relationships AS l
ON
l.clientid = c.id
AND
c.sms = '1'
AND
( l.listid = '1'
OR l.listid = '2' );
GROUP BY
c.id
To return just the clients participating in more than 1 list you may want to consider using the HAVING clause:
SELECT c.id
FROM Clients c
INNER JOIN Client_Lists_Relationships l
ON l.clientid = c.id
WHERE c.sms = 1
HAVING COUNT(L.listid) > 1
GROUP BY c.id