I need to know the COUNT of a query, and also the same query with a HAVING clause
By way of illustration (not the real case, but illustrative), if table pupilTable contains a list of pupil and their class, and I want to know the number of classes, and also the number of classes with more than 25 children:
I know I can get the total number of classes using:
SELECT COUNT( * ) AS NumAllClasses FROM pupilTable GROUP BY class
I know I can get the number of big classes with the condition using:
SELECT COUNT( * ) AS NumBigClasses FROM pupilTable GROUP BY class HAVING COUNT(pupil) > 25
Is there a simple (single query) way of getting both at the same time? Google has not been my friend :(
Edited to add illustrative data
Without any verification:
SELECT COUNT(*) AS count1 FROM table WHERE condition UNION ALL
SELECT COUNT(*) AS count2 FROM table WHERE condition HAVING second-condition
But note that i guess the second label will get lost so you will have both count-nrs returned under the label count1
You can user the following query:
select count(users.id) count1, count(u.id) count2 from users left join users u on users.id = u.id and u.fname = "abc" where users.id > 10
Here, I have used two conditions. You need to make relevant changes in this query to get desired output.
Here, user. and u. are the conditions.
In above query,
user.<condition1> : u.fname = "abc"
u.<condition2> : users.id > 10
Related
Suppose I have two tables, users and posts. Posts has the following fields, userid, postid, etc and userid can appear multiple times as one user can write multiple posts....I'm just trying sort the users table based off the # of occurrences per userid in the posts table. I can get the # of occurrences per user using this
SELECT userid, COUNT(*)
FROM posts
GROUP BY userid;
I would like to use the values under COUNT(*) column, maybe add it to my other table because then I can simply to something like this
SELECT * FROM users
ORDER BY newcolumn ASC;
but I'm having trouble doing that. Or can I do it without having to add an extra column? Hints please. Thanks
Left join is the key here!
SELECT users.userid,count(posts.userid) AS total_count
FROM users
LEFT JOIN posts on posts.userid = users.userid
GROUP BY users.userid
ORDER BY total_count DESC;
We are taking the left join on two tables with same user_id and we are counting the total number of posts per user using group by. Finally sort by count and show results.
try an left join:
select users.userid, [user fields],count(postid) as posts_count
from users
left join posts on posts.userid = users.userid
group by users.userid,[user fields]
order by posts_count desc.
You want to select users (FROM users) but you want to sort based on criteria in another table (COUNT(*) FROM posts) -- therefore you need to use a JOIN
Off-hand I can't seem to recall if "JOIN" or "RIGHT JOIN" or "FULL JOIN" is what you need if you wanted to get a cartesian product of the tables then group and aggregate on a single field, but I can avoid the need to remember with a subquery (hopefully someone will soon post a smaller and smarter answer):
SELECT users.* FROM users
JOIN (
SELECT userid, COUNT(*) as count
FROM posts
GROUP BY userid
) as subquery ON users.id = subquery.userid
ORDER BY subquery.count
Note: I haven't tested this query, but it looks good to me. Again: hopefully someone will post a better answer soon as I'm not doing my due dilligence, but you definitely need a JOIN :)
You could add a post_count column to the users table, but you would also have to update that count column every time a user creates a new post and you would have to build that logic into your application.
Otherwise, it looks like the answer from FallAndLearn will get you what you need.
I'm working on a project and I have a problem. I have a table namedfriendswith three columnid,from_emailandto_email(it's a social networking site and "from_email" is the person that follows the "to_email"). I want a query to return the top 5 friends I follow according to the number of their followers. I know that the query for top 5 is:
SELECT
to_mail,
COUNT(*) AS friendsnumber
FROM
friends
GROUP BY
to_email
ORDER BY
friendsnumber DESC
LIMIT 5
Any ideas?
I would also like to return friends with the same number of followers ordered by their name. Is it possible?
You should use COUNT(from_email) instead of COUNT(*); because you want to calculate the number of followers, which is represented by from_email.
Thus, your select clause would be something like:
SELECT to_email, COUNT(from_email) as magnitude
as for getting the most popular people that you follow, you could use IN clause:
WHERE to_email IN (SELECT to_email FROM friends WHERE from_email='MY_EMAIL');
and about name, you shall join this query with the other table which contains the name value.
Since you've got the essentials now, I hope you can try to compose the full query on your own =)
Join again to the table for the 2nd tier count:
SELECT f1.to_email
FROM friends f1
JOIN friends f2 on f2.to_mail = f1.to_email
WHERE f1.from_email = 'myemail'
GROUP BY 1
ORDER BY count(*) DESC
LIMIT 5
If an index is defined on to_email, this will perform very well.
I have an SQL query which calculates a sum of values for a certain column and also needs to retrieve a single value, both from the same table.
I was wondering, since the whole table will be read to calculate the sum, is there a way I can select the wanted value at the same moment ?
Is this possible or do I need to make 2 distinct SELECTs on the table as shown below?
The current code from my query is :
SELECT [columns],
(SELECT SUM(value) FROM votes WHERE postid=p.postid) AS charge,
(SELECT value FROM votes WHERE postid=p.postid AND userid=u.userid) AS currentVote
FROM posts p, users u WHERE p.userid=u.userid
Thanks !
In your specific case it is possible as you want the SUM of the value for votes related to the posts for a specific user.
Instead of using nested queries you could use something like this:
Based on the Comments I have updated the query:
SQL Fiddle: http://www.sqlfiddle.com/#!2/2a0920/9
SELECT p.postid, sum(v.value) AS charge,
v.value AS currentVote
FROM posts p,
users u,
votes v
WHERE p.userid=u.userid
AND v.postid = p.postid
group by p.postid;
I have three tables: users, groups and relation.
Table users with fields: usrID, usrName, usrPass, usrPts
Table groups with fields: grpID, grpName, grpMinPts
Table relation with fields: uID, gID
User can be placed in group in two ways:
if collect group minimal number of points (users.usrPts > group.grpMinPts ORDER BY group.grpMinPts DSC LIMIT 1)
if his relation to the group is manually added in relation tables (user ID provided as uID, as well as group ID provided as gID in table named relation)
Can I create one single query, to determine for every user (or one specific), which group he belongs, but, manual relation (using relation table) should have higher priority than usrPts compared to grpMinPts? Also, I do not want to have one user shown twice (to show his real group by points, but related group also)...
Thanks in advance! :) I tried:
SELECT * FROM users LEFT JOIN (relation LEFT JOIN groups ON (relation.gID = groups.grpID) ON users.usrID = relation.uID
Using this I managed to extract specified relations (from relation table), but, I have no idea how to include user points, respecting above mentioned priority (specified first). I know how to do this in a few separated queries in php, that is simple, but I am curious, can it be done using one single query?
EDIT TO ADD:
Thanks to really educational technique using coalesce #GordonLinoff provided, I managed to make this query to work as I expected. So, here it goes:
SELECT o.usrID, o.usrName, o.usrPass, o.usrPts, t.grpID, t.grpName
FROM (
SELECT u.*, COALESCE(relationgroupid,groupid) AS thegroupid
FROM (
SELECT u.*, (
SELECT grpID
FROM groups g
WHERE u.usrPts > g.grpMinPts
ORDER BY g.grpMinPts DESC
LIMIT 1
) AS groupid, (
SELECT grpUID
FROM relation r
WHERE r.userUID = u.usrID
) AS relationgroupid
FROM users u
)u
)o
JOIN groups t ON t.grpID = o.thegroupid
Also, if you are wondering, like I did, is this approach faster or slower than doing three queries and processing in php, the answer is that this is slightly faster way. Average time of this query execution and showing results on a webpage is 14 ms. Three simple queries, processing in php and showing results on a webpage took 21 ms. Average is based on 10 cases, average execution time was, really, a constant time.
Here is an approach that uses correlated subqueries to get each of the values. It then chooses the appropriate one using the precedence rule that if the relations exist use that one, otherwise use the one from the groups table:
select u.*,
coalesce(relationgroupid, groupid) as thegroupid
from (select u.*,
(select grpid from groups g where u.usrPts > g.grpMinPts order by g.grpMinPts desc limit 1
) as groupid,
(select gid from relations r where r.userId = u.userId
) as relationgroupid
from users u
) u
Try something like this
select user.name, group.name
from group
join relation on relation.gid = group.gid
join user on user.uid = relation.uid
union
select user.name, g1.name
from group g1
join group g2 on g2.minpts > g1.minpts
join user on user.pts between g1.minpts and g2.minpts
I'm trying to compare two set of resutls aving hard time to undesrtand how subqueries work and if they are efficient. I'm not gonna explain all my tables, but just think i have apair of arrays...i might do it in php but i wonder if i can do it in mysql right away...
this is my query to check how many items user 1 has in lists he owns
SELECT DISTINCT *
FROM list_tb
INNER JOIN item_to_list_tb
ON list_tb.list_id = item_to_list_tb.list_id
WHERE list_tb.user_id = 1
ORDER BY item_to_list_tb.item_id DESC
this is my query to check how many items user 2 has in lists he owns
SELECT DISTINCT *
FROM list_tb
INNER JOIN item_to_list_tb
ON list_tb.list_id = item_to_list_tb.list_id
WHERE list_tb.user_id = 1
ORDER BY item_to_list_tb.item_id DESC
now the problem is that i would intersect those results to check how many item_id they have in common...
thanks!!!
Unfortunately, MySQL does not support the Intersect predicate. However, one way to accomplish that goal would be to exclude List_Tb.UserId from your Select and Group By and then count by distinct User_Id:
Select ... -- everything except List_Tb.UserId
From List_Tb
Inner Join Item_To_List_Tb
On List_Tb.List_Id = Item_To_List_Tb.List_Id
Where List_Tb.User_Id In(1,2)
Group By ... -- everything except List_Tb.UserId
Having Count( Distinct List_Tb.User_Id ) = 2
Order By item_to_list_tb.item_id Desc
Obviously you would replace the ellipses with the actual columns you want to return and on which you wish to group.