I need to get the count from one of the sub tables / joined tables involved in the query. I will demonstrate with a simple example:
Table: user
id name etc
-------------------------------------------
1 u1
2 u2
Table: exercise
id userId etc
-------------------------------------------
1 1
2 1
Now I need to select from user table various fields like id, name, etc along with the count of various user id in exercise table.
For example, in the above case I need the output:
id name count
-------------------------------------------
1 u1 2 --since two u1's are present in exercise
2 u2 0 --since no u2's are present in exercise
I tried this: but I get syntax error:
--actual query is very complex
SELECT u.id, u.name, COUNT(e.*)
FROM user AS u
JOIN exercise AS e ON u.id = e.userId
I tried this: but I get syntax error again:
--actual query is very complex
SELECT u.id, u.name, (SELECT COUNT(*) FROM e)
FROM user AS u
JOIN exercise AS e ON u.id = e.userId
This works, as a sub query, but is painfully slow (5 to 13 seconds for about 10000 rows in each table):
--actual query is very complex
SELECT u.id, u.name, (SELECT COUNT(*) FROM exercise WHERE e.userId = u.id)
FROM user AS u
Is there a way I can get the count info in one single query, with the help of join or so? Sub query is very slow for my needs.
Try using a GROUP BY, like this:
SELECT u.id, u.name, COUNT(e.userId)
FROM user AS u
LEFT JOIN exercise AS e
ON u.id = e.userId
GROUP BY u.id
Try this:
SELECT u.id, u.name, COUNT(e.userId)
FROM user AS u
LEFT JOIN exercise AS e
ON u.id = e.userId
GROUP BY u.id,u.name
Left join will still return you row from user table even if there are no records in exercise table.
Related
I have 2 tables: user and review, a one-to-many relationship.
When I execute the following query:
SELECT
user_id,
count(*) totalReviews,
USER . NAME
FROM
review,
USER
WHERE
USER .id = review.user_id
GROUP BY
user_id
I get:
1 2 marius
2 2 daniela
3 1 alin
What I want to do now is to display first 2 users because they have given the most reviews(2).
I tried adding having, if I hardcode having totalReviews=2 it works, but if I write having total = max(total) I get 0 results, while if I'm trying with,
SELECT
*
FROM
(
SELECT
user_id,
count(*) total,
USER . NAME
FROM
review,
USER
WHERE
USER .id = review.user_id
GROUP BY
user_id
) A
WHERE
total = (SELECT max(total) FROM A) `
I get an error (table A doesn't exist)
You would do this with ORDER BY and LIMIT:
SELECT u.id, count(*) as totalReviews, u.name
FROM review r JOIN
user u
ON u.id = r.user_id
GROUP BY u.id, u.name
ORDER BY totalReviews DESC
LIMIT 2;
Notes:
Never use commas in the FROM clause. Always use proper, explicit JOIN syntax.
Table aliases make the query easier to write and read.
EDIT:
If occurs to me that you want all users with the maximum number of reviews, not exactly 2. Here is one method:
SELECT u.id, COUNT(*) as totalReviews, u.name
FROM review r JOIN
user u
ON u.id = r.user_id
GROUP BY u.id, u.name
HAVING totalReviews = (SELECT COUNT(*)
FROM review r2
GROUP BY r2.user_id
ORDER BY COUNT(*) DESC
LIMIT 1
);
Note that the subquery in the HAVING clause is simpler than the outer query. There is no need to bring in the user name.
SELECT DISTINCT u.id AS userId,u.type AS userType
FROM User AS u,Personal AS p,Company AS c
WHERE (p.realName LIKE '%adf%' AND u.type=1 AND u.id=p.userId)
OR (c.name LIKE '%grge%' AND u.id=c.userId)
LIMIT 0 , 10000
You can write your query as:
SELECT DISTINCT u.id AS userId,u.type AS userType
FROM User AS u inner join Personal AS p on u.id=p.userId
inner join Company AS c on u.id=c.userId
where p.realName LIKE '%adf%' or c.name LIKE '%grge%'
LIMIT 0 , 10000
Try to avoid comma seperated JOINS
You appear to be doing a quite hideous cross join, and then selectively narrowing down the records in the WHERE clause.
It is probably better to do 2 queries and union the results together. Each query can do one proper join. It is still going to have to access one column using the LIKE, and with a leading wild card that is not going to be quick (it can't use indexes).
SELECT u.id AS userId,
u.type AS userType
FROM User AS u
INNER JOIN Personal AS p
ON u.id = p.userId
WHERE p.realName LIKE '%adf%'
AND u.type = 1
UNION
SELECT u.id AS userId,
u.type AS userType
FROM User AS u
INNER JOIN Company AS c
ON u.id=c.userId
WHERE c.name LIKE '%grge%'
LIMIT 0 , 10000
I'm trying to join multiple table to get single row result for each id. This result will be send to angular UI
I have 3 tables user, friends and trip
A user can have multiple friends but one trip
I like to get all details corresponding to a user in one row, probably friends as field like an array?
This is how my table looks.
http://sqlfiddle.com/#!9/0879d/2
https://gist.github.com/tomalex0/9dee4fff85583732e7d0
group_concat should do the trick for you:
SELECT u.*, t.*, friendlist
FROM user u
LEFT JOIN trip t ON u.id = t.user_id
LEFT JOIN (SELECT user_id, GROUP_CONCAT(CONCAT (name, '- ', email)) friendlist
FROM friends
GROUP BY user_id) f ON f.user_id = u.id
I'm trying to write a script that will export modx users to CSV, fairly straightforward stuff, but in modx users can belong to many groups. Simply joining the modx_member_groups table will result in several rows for different users.
What I would like to do is somehow rewrite the query below so that the join on the modx_member_groups would return a list or array of group ids that the user belongs to.
For example, I would like the returned data to look like:
user_group | id | username | ...the rest
1,3,5,7 | 12 | johndoe | ...
here is the query I have.
SELECT mg.user_group, u.id, u.username, ua.*
FROM modx_users u
LEFT JOIN modx_user_attributes ua ON u.id = ua.internalKey
LEFT JOIN modx_member_groups mg ON u.id = mg.member
LIMIT 10
Ideally it would be awesome to somehow select the actual group names as columns. and then just force a true or false in the group name column.
UPDATE
I've updated the query after shtever's answer but have performance issues:
- GROUP_CONCAT was returning a BLOB type so I had to convert it, setting the group_concat_max_length to below 512 was not working
SELECT GROUP_CONCAT(CONVERT(mg.user_group, CHAR(10)) ORDER BY mg.user_group SEPARATOR ',') AS groups, u.id, u.username, ua.*
FROM modx_users u
LEFT JOIN modx_user_attributes ua ON u.id = ua.internalKey
LEFT JOIN modx_member_groups mg ON mg.member = u.id
GROUP BY u.id
The query now takes 27.5 seconds to execute if I limit it to 10 results or let it run on the entire 6000 users it always takes 27.5 seconds. If I remove the GROUP_CONCAT ~ same amount of time.
For MySQL, take a look at the GROUP_CONCAT function. Mysql GROUP_CONCAT Description
Your query might look something like:
SELECT GROUP_CONCAT(DISTINCT mg.user_group ASC SEPARATOR ',') , u.id, u.username, ua.*
FROM modx_users u
LEFT JOIN modx_user_attributes ua ON u.id = ua.internalKey
LEFT JOIN modx_member_groups mg ON u.id = mg.member
GROUP BY u.id, u.username
LIMIT 10
You might have to fiddle with the GROUP BY fields depending on the relation between the modx_user_attributes and modx_users table.
I have two table user and follow. I want to write view such that it will fetch all details of particular user along with that two extra column as follower count and followee count alias.
eg. user id=11 then all details from user tables plus followcount 1 and followed count1
SELECT u.id,
u.userid,
u.name,
u.mobile,
(SELECT Count(*)
FROM follow f
WHERE f.followerid = u.userid) AS follower,
(SELECT Count(*)
FROM follow f
WHERE f.followeeid = u.userid) AS followee
FROM users u
You can achieve this is by using JOIN statements in your query:
example of how you can achieve your final result:
CREATE VIEW [Followers] AS
SELECT a.name, a.email, a.mobile, COUNT(SELECT COUNT(followerID) FROM follow WHERE followerID = a.userid), COUNT(SELECT COUNT(followeeID) FROM follow WHERE followeeID = a.userid) FROM users a INNER JOIN follow b ON b.followerID = a.userid