I have a working query using INNER JOIN and a subquery but was wondering if there is a more effient way of writing it.
with prl
as
(
SELECT `number`, creator, notes
FROM ratings
INNER JOIN
projects on ratings.project_id = projects.project_id
WHERE ratings.rating = 5 AND projects.active = 1
)
SELECT prl.`number`, creator, notes
FROM prl
INNER JOIN(
SELECT `number`
HAVING COUNT(creator) > 1
)temp ON prl.`number` = temp.`number`
ORDER BY temp.`number`
projects table
project_id| number | creator | active |
| 1 | 3 | bob | 1 |
| 2 | 4 | mary | 1 |
| 3 | 5 | asi | 1 |
rating table
project_id| notes | rating |
| 1 | note1 | 5 |
| 1 | note2 | 5 |
| 3 | note3 | 5 |
| 1 | note4 | 1 |
| 2 | note5 | 5 |
| 3 | note6 | 2 |
result
| number | creator | notes |
| 3 | bob | note1 |
| 3 | bob | note2 |
It seems like you're using MySQL version that support window function. If so, then try this:
SELECT number, creator, notes
FROM
(SELECT p.number, p.creator, r.notes,
COUNT(creator) OVER (PARTITION BY creator) AS cnt
FROM project p
JOIN rating r ON p.project_id=r.project_id
WHERE r.rating=5
AND p.active = 1) v
WHERE cnt=2;
As far as whether this is more efficient, I'm not really sure because it depends in your table indexes but for a small dataset, I assume this will do well.
Demo fiddle
I'm trying to figure out a MYSQL string and my noob-ness is getting in my way. I'm trying to count the total number of teams per phase.
Tables to consider:
phases
+----+------------+
| id | phase_name |
+----+------------+
| 1 | start |
| 2 | middle |
| 3 | end |
| 4 | finish |
+----+------------+
teams
+----+-----------+----------+
| id | team_name | phase_id |
+----+-----------+----------+
| 1 | team1 | 2 |
| 2 | team2 | 3 |
| 3 | team3 | 3 |
| 4 | team4 | 4 |
| 4 | team5 | 3 |
+----+-----------+----------+
Desired result
+----------+------------+-----------+
| phase_id | phase_name | tot_teams |
+----------+------------+-----------+
| 1 | start | NULL |
| 2 | middle | 1 |
| 3 | end | 3 |
| 4 | finish | 1 |
+----------+------------+-----------+
I've tried:
SELECT
T.phase_id, P.phase_name, COUNT(*) AS tot_teams
FROM
teams T
LEFT JOIN
phases P ON P.id = T.phase_id
GROUP BY
phase_id;
but that only shows the affected phase_id's...and I'm hoping to get ALL phase_id's in a table. I also tried:
SELECT
P.phase_name, T.phase_id, COUNT(*)
FROM
teams T
RIGHT JOIN
phases P on P.`id` = T.`phase_id`
GROUP BY
P.id
but that shows invalid data. (For example, phase_id has a qty of 1 but doesn't show up in the teams table.
Can you point me in the right direction?
Thanks!
The RIGHT JOIN is correct, but you need to use COUNT(T.phase_id) instead of COUNT(*). Otherwise, you're counting the row containing NULL that's generated for the phase with no teams.
Most people prefer to use LEFT JOIN, putting the master table first.
SELECT P.phase_name, P.phase_name, COUNT(T.phase_id)
FROM phase AS P
LEFT JOIN teams AS T ON P.id = T.phase_id
GROUP BY P.id
I have two tables users and services and i am try to write a single query that will create a new column skills. The values in the column skills will be the service_title which maps to the service_id stored in user_skills.
Below are the examples of a the tables used:
Table users:
+---------+---------------+----------------+----------------+
| id | user_fname | user_lname | user_skills |
+---------+---------------+----------------+----------------+
| 1 | kiran | bhattarai | 1,2 |
| 2 | sujan | bhattarai | 2,4 |
| 3 | manorath | dad | 1,2,3,4 |
| 4 | bhagawoti | mom | 2,3 |
+---------+---------------+----------------+----------------+
Table services:
+-----------------+------------------+
| service_id | service_title |
+-----------------+------------------+
| 1 | cook |
| 2 | clean |
| 3 | grocessery |
| 4 | teach |
+-----------------+------------------+
Currently i am using this query:
SELECT users.user_fname,
users.user_lname,
(SELECT GROUP_CONCAT(service_title)
FROM `services`
WHERE `service_id` IN (1,2,3,4)) as skills
FROM users
WHERE
id =3;
Result of the above query:
+---------------+----------------+----------------------------------------+
| user_fname | user_lname | skills |
+---------------+----------------+----------------------------------------+
| manorath | dad | cook,clean,grocessery,teach |
+---------------+----------------+----------------------------------------+
Instead of using the IN (1,2,3,4) I tried IN (users.user_skills) because the values in user_skills changes all the time and the result was:
+---------------+----------------+----------------------------------------+
| user_fname | user_lname | skills |
+---------------+----------------+----------------------------------------+
| manorath | dad | cook |
+---------------+----------------+----------------------------------------+
Every time a new service is added i have to add that service_id in the IN (1,2,3,4,new service id) of my query which is not a proper solution. I have already tried using php and another query to do solve this, the disadvantage of doing that is it is slowing down the process. How should i solve this problem in a single query.
You can use FIND_IN_SET() to JOIN the two tables.
SELECT
u.user_fname,
u.user_lname,
GROUP_CONCAT(s.service_title) as skills
FROM users u
LEFT JOIN services s
ON FIND_IN_SET(s.service_id, u.user_skills)
WHERE u.id = 3
Note that a JOIN with a FIND_IN_SET() condition cannot utilize any index. And that can lead to poor performance.
In general it's a bad idea to store relations in a separated string column. See Is storing a delimited list in a database column really that bad?.
You should normalize your design and create a separate table for your many-to-many relation. The table would look like
Table users_services:
+---------+------------+
| user_id | service_id |
+---------+------------+
| 1 | 1 |
| 1 | 2 |
| 2 | 2 |
| 2 | 4 |
| 3 | 1 |
| 3 | 2 |
| 3 | 3 |
| 3 | 4 |
| 4 | 2 |
| 4 | 3 |
+---------+------------+
And the query would be
SELECT
u.user_fname,
u.user_lname,
GROUP_CONCAT(s.service_title) as skills
FROM users u
LEFT JOIN users_services us ON us.user_id = u.id
LEFT JOIN services s ON s.service_id = us.service_id
WHERE u.id = 3
I have two tables, users and survey. I want query the table user and to join the table survey in a way that only the survey record with the lowest value is returned for each record in user table.
I want to avoid subqueries and temporary tables.
table users:
--------------
| uid | name |
--------------
| 1 | mike |
| 2 | john |
| 3 | bill |
--------------
table survey:
----------------------
| id | uid | value |
----------------------
| 1 | 3 | 9 |
| 2 | 3 | 5 |
| 3 | 1 | 3 |
| 4 | 1 | 7 |
| 5 | 1 | 2 |
| 6 | 2 | 4 |
| 7 | 2 | 9 |
| 8 | 1 | 0 |
| 9 | 2 | 5 |
---------------------
expected output:
---------------------
| id | name | value |
---------------------
| 8 | mike | 0 |
| 2 | bill | 5 |
| 6 | john | 4 |
---------------------
What kind of JOIn should I do, or how should I write the query?
The following query gets all rows with minimum value (doesn't exist another survey with value under the selected value)
Try this:
SELECT u.*, s.value
FROM survey s
JOIN users u
ON s.uid = u.uid
WHERE NOT EXISTS(
SELECT 'maximum'
FROM survey s2
WHERE s2.uid = s.uid
AND s2.value < s.value)
You could use something like this:
select s.id, u.name, y.min_value
from
(
select uid, min(value) as min_value
from survey
group by uid
) y
join survey s
on s.value = y.min_value
and s.uid = y.uid
join user u
on u.uid = y.uid
I think this will help you
SELECT * FROM SURVEY S
INNER JOIN USERS U
ON S.UID=U.UID
QUALIFY ROW_NUMBER() OVER (PARTITION BY S.UID ORDER BY S.VALUE1 ASC )=1;
Here is the case I have two tables tags and customers as the following structure
Tags Table
ID Name
1 Tag1
2 Tag2
Customers Table
ID Tag_ID Name
1 1 C1
2 2 C2
3 1 C3
I want a SQL statement to get the first 10 customers (alphabetically) for each tag? is it possible to be done in one query.
P.S the data in the tables are sample data not the actual data
Consider the following:
DROP TABLE IF EXISTS tags;
CREATE TABLE tags
(tag_id INT NOT NULL AUTO_INCREMENT PRIMARY KEY
,name VARCHAR(12) NOT NULL
);
INSERT INTO tags VALUES
(1,'One'),
(2,'Two'),
(3,'Three'),
(4,'Four'),
(5,'Five'),
(6,'Six');
DROP TABLE IF EXISTS customers;
CREATE TABLE customers
(customer_id INT NOT NULL
,customer VARCHAR(12)
);
INSERT INTO customers VALUES
(1,'Dave'),
(2,'Ben'),
(3,'Charlie'),
(4,'Michael'),
(5,'Steve'),
(6,'Clive'),
(7,'Alice'),
(8,'Ken'),
(9,'Petra');
DROP TABLE IF EXISTS customer_tag;
CREATE TABLE customer_tag
(customer_id INT NOT NULL
,tag_ID INT NOT NULL
,PRIMARY KEY(customer_id,tag_id)
);
INSERT INTO customer_tag VALUES
(1,1),
(1,2),
(1,4),
(2,3),
(2,2),
(3,1),
(4,4),
(4,2),
(5,2),
(5,5),
(5,6),
(6,6);
The following query returns all customers associated with each tag, and their respective 'rank' when sorted alphabetically...
SELECT t.*, c1.*, COUNT(ct2.tag_id) rank
FROM tags t
JOIN customer_tag ct1
ON ct1.tag_id = t.tag_id
JOIN customers c1
ON c1.customer_id = ct1.customer_id
JOIN customer_tag ct2
ON ct2.tag_id = ct1.tag_id
JOIN customers c2
ON c2.customer_id = ct2.customer_id
AND c2.customer <= c1.customer
GROUP
BY t.tag_id, c1.customer_id
ORDER
BY t.tag_id,rank;
+--------+-------+-------------+----------+------+
| tag_id | name | customer_id | customer | rank |
+--------+-------+-------------+----------+------+
| 1 | One | 3 | Charlie | 1 |
| 1 | One | 1 | Dave | 2 |
| 2 | Two | 2 | Ben | 1 |
| 2 | Two | 1 | Dave | 2 |
| 2 | Two | 4 | Michael | 3 |
| 2 | Two | 5 | Steve | 4 |
| 3 | Three | 2 | Ben | 1 |
| 4 | Four | 1 | Dave | 1 |
| 4 | Four | 4 | Michael | 2 |
| 5 | Five | 5 | Steve | 1 |
| 6 | Six | 6 | Clive | 1 |
| 6 | Six | 5 | Steve | 2 |
+--------+-------+-------------+----------+------+
If we just want the top 2, say, for each tag, we can rewrite that as follows...
SELECT t.*
, c1.*
FROM tags t
JOIN customer_tag ct1
ON ct1.tag_id = t.tag_id
JOIN customers c1
ON c1.customer_id = ct1.customer_id
JOIN customer_tag ct2
ON ct2.tag_id = ct1.tag_id
JOIN customers c2
ON c2.customer_id = ct2.customer_id
AND c2.customer <= c1.customer
GROUP
BY t.tag_id, c1.customer_id
HAVING COUNT(ct2.tag_id) <=2
ORDER
BY t.tag_id, c1.customer;
+--------+-------+-------------+----------+
| tag_id | name | customer_id | customer |
+--------+-------+-------------+----------+
| 1 | One | 3 | Charlie |
| 1 | One | 1 | Dave |
| 2 | Two | 2 | Ben |
| 2 | Two | 1 | Dave |
| 3 | Three | 2 | Ben |
| 4 | Four | 1 | Dave |
| 4 | Four | 4 | Michael |
| 5 | Five | 5 | Steve |
| 6 | Six | 6 | Clive |
| 6 | Six | 5 | Steve |
+--------+-------+-------------+----------+
This is fine, but where performance is an issue, a solution like the following will be faster - although you may need to run SET NAMES utf8; prior to constructing the tables (as I had to) in order for it to work properly:
SELECT tag_id, name, customer_id,customer
FROM
(
SELECT t.*
, c.*
, CASE WHEN #prev=t.tag_id THEN #i:=#i+1 ELSE #i:=1 END rank
, #prev := t.tag_id
FROM tags t
JOIN customer_tag ct
ON ct.tag_id = t.tag_id
JOIN customers c
ON c.customer_id = ct.customer_id
JOIN ( SELECT #i:=1, #prev:=0) vars
ORDER
BY t.tag_id
, c.customer
) x
WHERE rank <=2
ORDER
BY tag_id,customer;
+--------+-------+-------------+----------+
| tag_id | name | customer_id | customer |
+--------+-------+-------------+----------+
| 1 | One | 3 | Charlie |
| 1 | One | 1 | Dave |
| 2 | Two | 2 | Ben |
| 2 | Two | 1 | Dave |
| 3 | Three | 2 | Ben |
| 4 | Four | 1 | Dave |
| 4 | Four | 4 | Michael |
| 5 | Five | 5 | Steve |
| 6 | Six | 6 | Clive |
| 6 | Six | 5 | Steve |
+--------+-------+-------------+----------+
To achieve this, we have to use two session variables, one for the row number and the other for storing the old customer ID to compare it with the current one as the following query:
select c.name, #row_number:=CASE
WHEN #cid = c.id THEN #row_number + 1
ELSE 1
END AS rows,
#id:=c.id as CustomerId from tags t, customers c where t.id=c.id group by c.name where Rows<=10
We used CASE statement in the query. If the customer number remains the same, we increase the row_number variable
Reference
Your question reminds me of this one (see especially the top-voted answer), so I came up with this query:
SELECT Tags.ID,
Tags.Name,
SUBSTRING_INDEX(GROUP_CONCAT(Customers.Name
ORDER BY Customers.Name),
',', 10) AS Customers
FROM Customers
INNER JOIN Tags
ON Tags.ID = Customers.Tag_ID
GROUP BY Tags.ID
ORDER BY Tags.Id;
It works, but this is clearly a hacky way to do this, because MySQL does not offer yet tools to do this more naturally.