I'm new to MySQL, and I'd like some help in setting up a MySQL query to pull some data from a few tables (~100,000 rows) in a particular output format.
This problem involves three SQL tables:
allusers : This one contains user information. The columns of interest are userid and vip
table1 and table2 contain data, but they also have a userid column, which matches the userid column in allusers.
What I'd like to do:
I'd like to create a query which searches through allusers, finds the userid of those that are VIP, and then count the number of records in each of table1 and table2 grouped by the userid. So, my desired output is:
userid | Count in Table1 | Count in Table2
1 | 5 | 21
5 | 16 | 31
8 | 21 | 12
What I've done so far:
I've created this statement:
SELECT userid, count(1)
FROM table1
WHERE userid IN (SELECT userid FROM allusers WHERE vip IS NOT NULL)
GROUP BY userid
This gets me close to what I want. But now, I want to add another column with the respective counts from table2
I also tried using joins like this:
select A.userid, count(T1.userid), count(T2.userid) from allusers A
left join table1 T1 on T1.userid = A.userid
left join table2 T2 on T2.userid = A.userid
where A.vip is not null
group by A.userid
However, this query took a very long time and I had to kill the query. I'm assuming this is because using Joins for such large tables is very inefficient.
Similar Questions
This one is looking for a similar result as I am, but doesn't need nearly as much filtering with subqueries
This one sums up the counts across tables, while I need the counts separated into columns
Could someone help me set up the query to generate the data I need?
Thanks!
You need to pre-aggregate first, then join, otherwise the results will not be what you expect if a user has several rows in both table1 and table2. Besides, pre-aggregation is usually more efficient than outer aggregation in a situation such as yours.
Consider:
select a.userid, t1.cnt cnt1, t2.cnt cnt2
from allusers a
left join (select userid, count(*) cnt from table1 group by userid) t1
on t1.userid = a.userid
left join (select userid, count(*) cnt from table2 group by userid) t2
on t2.userid = a.userid
where a.vip is not null
This is a case where I would recommend correlated subqueries:
select a.userid,
(select count(*) from table1 t1 where t1.userid = a.userid) as cnt1,
(select count(*) from table2 t2 where t2.userid = a.userid) as cnt2
from allusers a
where a.vip is not null;
The reason that I recommend this approach is because you are filtering the alllusers table. That means that the pre-aggregation approach may be doing additional, unnecessary work.
Related
I have table like this one:
I would like to all rows, but if there is user_id 5 if this case, override other rows which have no user_id.
I tried both with MAX(user_id) and GROUP BY country_name, but it still returns, wrong results.
Final result I'm expecting:
Try this;)
select t1.*
from yourtable t1
inner join (
select max(user_id) as user_id, country_name from yourtable group by country_name
) t2 on t1.country_name = t2.country_name and t1.user_id = t2.user_id
This is just a solution based on your sample data. If you have a variety of user_id, it should be more different.
As of SQL Select only rows with Max Value on a Column you can easily get rows with max value on a column by using both MAX(column) and GROUP BY other_column in one statement.
But if you want to select other columns too, you have to this in a subquery like in the following example:
SELECT a.*
FROM YourTable a
INNER JOIN (
SELECT country_name, MAX(user_id) user_id
FROM YourTable
GROUP BY country_name
) b ON a.country_name = b.country_name AND a.user_id = b.user_id
I have 3 tables and want to join all in one query to show latest 10 entries by datetime.
t1: id, username
t2: id, id_t1, med_id, ga_id, au_id, re_id, text, datetime
t3: id, id_t1, pro_id, au_id, re_id, text, datetime
First I saw it would be easy with simple left join and where id, but i got double results. Then i tried inner and outer join, also group by, but the result was bad.
So my question is how can i join all without double results of the last 10 of t2 and t3?
Hard to tell what exactly you are trying to acheive, but here is a clue how it could be complemented.
SELECT TOP 10 DISTINCT T1.*
FROM T1
INNER JOIN T2 ON T1.id = T2.id_t1
INNER JOIN T3 ON T1.id = T3.id_t1
ORDER BY (CASE WHEN T2.[DateTime] > T3.[DateTime] THEN
T2.[DateTime]
ELSE
T3.[DateTime]
END) DESC
If you need to select field from T2 and T3, GROUP BY on all T1 field with aggregate on field from t2 and t3 is an option. Otherwise, linked-subquery is the way to go.
As sgeddes commented already, it's hard to know what you need, without seeing some example data from your tables. It would really help to know what the relationship between the three tables is.
One question I have, in particular, is: how are t2 and t3 related, if at all? It looks like they might not be, as each of them has its own datetime column.
Perhaps the following could do the job, but we need some more info to know for sure:
(SELECT DISTINCT t1.*, t2.id, t2.au_id, t2.re_id, t2.text, t2.`datetime`, t2.med_id, t2.ga_id, NULL AS pro_id
FROM t1
INNER JOIN t2 ON t1.id = t2.id_t1)
UNION
(SELECT DISTINCT t1.*, t3.id, t3.au_id, t3.re_id, t3.text, t3.`datetime`, NULL AS med_id, NULL AS ga_id, t3.pro_id
FROM t1
INNER JOIN t3 ON t1.id = t3.id_t1)
ORDER BY datetime DESC
LIMIT 10
The following selects the username and the datetime for the last ten posts.
SELECT username, last_ten.`datetime` AS lastpost
FROM t1
INNER JOIN (
SELECT 't2' AS tab, id, `datetime`, t2.id_t1
FROM t2
UNION ALL
SELECT 't3' AS tab, id, `datetime`, t3.id_t1
FROM t3
ORDER BY datetime DESC
LIMIT 10
) AS last_ten ON t1.id = last_ten.id_t1
I have two tables, one holds user info (id, name, etc) and another table that holds user tickets and ticket status (ticket_id, user_id, ticket_status, etc).
I want to produce a list of ALL the users for example: ( SELECT * FROM user_table )
And for each user I need a count of their tickets for example:
(SELECT t1.user_id, COUNT(*) FROM user_tickets t1 WHERE t1.ticket_status = 15 GROUP BY t1.ticket_status, t1.user_id )
I can do this query to achieve what I’m looking for but it takes 5sec. to run the query on 50000 tickets, while each query running separately only takes fraction of a second.
SELECT t1.user_id, COUNT(*)
FROM user_tickets t1
LEFT JOIN user_table t2 ON t1.user_id = t2.id
WHERE t2.group_id = 20 AND t1.status_id = 15
GROUP BY t1.status_id, user_id
Any idea how to write the query to get same performance as each separately?
An indexing where clause fixed the problem.
I am trying to SELECT records from two MySql tables. I would like all records from the first table excluding specific records, by date, from the second table. For example:
Table1 T1id, firstName, LastName
Table2 id, T1id, hours, rate, date
T1id is the link between the two tables, therefore when the tables are joined I would have T1id, firstName, lastName, hours, rate, date
Let's say there is a record in Table2 with a date of 2012-02-08. With one query, I need to select all records from Table1, excluding the record from Table2 that has the date of 2012-02-08.
I've tried a few variations of JOINS and UNIONS, however I either get all records, a bunch of duplicate records, or one record (i.e. Table2 date). I apologize, but I do not have a specific piece of code to include since nothing has worked for me.
So many times this is typically done with a NOT EXISTS subquery, but subqueries can be big performance hits in larger tables... However, by doing a LEFT JOIN and looking for NULL is in essence, the same result
select
t1.*
from
table1 t1
left join table2 t2
on t1.t2.t1id
AND t2.date = '2012-02-08'
where
t2.t1id IS NULL
USE INNER JOIN if you are sure that T1id exists in both tables:
SELECT a.T1id,
a.FirstName,
a.LastName,
b.hours,
b.rate,
b.date
FROM table1 a INNER JOIN table2 b
ON a.T1id = b.T1id
WHERE b.date <> DATE('2012-02-08')
but if you want to get all T1id from Table1 (which exists or does not exists in Table2) use LEFT JOIN
SELECT a.T1id,
a.FirstName,
a.LastName,
b.hours,
b.rate,
b.date
FROM table1 a LEFT JOIN table2 b
ON a.T1id = b.T1id
WHERE b.date <> DATE('2012-02-08')
I'm trying to do a join between tables 1 and 2 which have a 1 to many relationship.
table1 has the following fields
createdate
contact
tkey (surrogate key)
table2 has the following fields
tkey (primary key)
status
userfld1
description
I want to show all items in table2 with their corresponding items in table1 grouped by table2.userfld1
select distinct t2.userfld1, t2.status, t2.description, t1.createdate, t1.contact
from table2 as t2 left join table1 as t1
on t2.tkey = t1.tkey
group by t2.userfld1
is this correct?
No that's not correct, you can't select columns that aren't in the group by unless they are contained in an aggregate function. And I think what you are asking for doesn't even make sense. My best guess is that you mean ORDER BY, not GROUP BY:
SELECT DISTINCT t2.userfld1, t2.status, t2.description, t1.createdate, t1.contact
FROM table2 t2
LEFT JOIN table1 t1
ON t2.tkey = t1.tkey
ORDER BY t2.userfld1
Three other errors that I've fixed:
SELECT ... FROM not SELECT ... WHERE
You should join with a table, not a column.
You had no aliases after the table names, but later refer to these missing aliases.
I think what you're looking for is order by, not group by, and I also fixed your query:
select t2.userfld1, t2.status, t2.description, t1.createdate, t1.contact
where table2 t2 left join table1 t1
on t2.tkey = t1.tkey
order by t2.userfld1
Is this what you were looking for?