Hits Table:
hid | lid | IP
1 | 1 | 123.123.123.123
2 | 1 | 123.123.123.123
3 | 2 | 123.123.123.123
4 | 2 | 123.123.123.123
5 | 2 | 123.123.123.124
6 | 2 | 123.123.123.124
7 | 3 | 123.123.123.124
8 | 3 | 123.123.123.124
9 | 3 | 123.123.123.124
As you can see, there following are the unique hits for the various lid:
lid 1: 1 unique hit
lid 2: 2 unique hits
lid 3: 1 unique hit
So basically, I need a query that will return the following:
lid | uhits |
1 | 1 |
2 | 2 |
3 | 1 |
Anybody know how to get that?
Select lid, count(distinct IP) as uhits
from hits
group by lid
Until you start getting into really complicated queries, SQL is made so it reads quite like a natural sentence. So first, if you can describe exactly what you want out of your query, you've already half written the SQL.
In this case, you can describe your problem like:
Get lid and the aggregate count of unique IP from my table for each lid.
The only thing that remains is to translate this, using SQL keywords. The important ones here being:
get -> SELECT
count -> COUNT
unique -> DISTINCT
aggregate..for each <field> -> SELECT <aggregate function>..GROUP BY <field>
So, your sentence above starts to look like:
SELECT lid and the aggregate COUNT of DISTINCT IP FROM my table GROUP BY lid.
Removing unnecessary words, and cleaning it up to use SQL syntax leaves the final query:
SELECT hits.lid, COUNT(DISTINCT hits.IP) AS uhits
FROM hits
GROUP BY hits.lid
SELECT lid, COUNT(DISTINCT IP)
FROM hits
GROUP BY lid
You need use group by:
SELECT lid, count(*)
FROM Table
GROUP BY lid
Related
class_table
+----+-------+--------------+
| id |teac_id| student_id |
+----+-------+--------------+
| 1 | 1 | 1,2,3,4 |
+----+-------+--------------+
student_mark
+----+----------+--------+
| id |student_id| marks |
+----+----------+--------+
| 1 | 1 | 12 |
+----+----------+--------+
| 2 | 2 | 80 |
+----+----------+--------+
| 3 | 3 | 20 |
+----+----------+--------+
I have these two tables and i want to calculate the total marks of student and my sql is:
SELECT SUM(`marks`)
FROM `student_mark`
WHERE `student_id` IN
(SELECT `student_id` FROM `class_table` WHERE `teac_id` = '1')
But this will return null, please help!!
DB fiddle
Firstly, you should never store comma separated data in your column. You should really normalize your data. So basically, you could have a many-to-many table mapping teacher_to_student, which will have teac_id and student_id columns.
In this particular case, you can utilize Find_in_set() function.
From your current query, it seems that you are trying to getting total marks for a teacher (summing up marks of all his/her students).
Try:
SELECT SUM(sm.`marks`)
FROM `student_mark` AS sm
JOIN `class_table` AS ct
ON FIND_IN_SET(sm.`student_id`, ct.`student_id`) > 0
WHERE ct.`teac_id` = '1'
In case, you want to get total marks per student, you would need to add a Group By. The query would look like:
SELECT sm.`student_id`,
SUM(sm.`marks`)
FROM `student_mark` AS sm
JOIN `class_table` AS ct
ON FIND_IN_SET(sm.`student_id`, ct.`student_id`) > 0
WHERE ct.`teac_id` = '1'
GROUP BY sm.`student_id`
Just in case you want to know why, The reason it returned null is because the subquery returned as '1,2,3,4' as a whole. What you need is to make it returned 1,2,3,4 separately.
What your query returned
SELECT SUM(`marks`)
FROM `student_mark`
WHERE `student_id` IN ('1,2,3,4')
What you expect is
SELECT SUM(`marks`)
FROM `student_mark`
WHERE `student_id` IN (1,2,3,4)
The best way is it normalize as #madhur said. In your case you need to make the teacher and student as one to many link
+----+-------+--------------+
| id |teac_id| student_id |
+----+-------+--------------+
| 1 | 1 | 1 |
+----+-------+--------------+
| 2 | 1 | 2 |
+----+-------+--------------+
| 3 | 1 | 3 |
+----+-------+--------------+
| 4 | 1 | 4 |
+----+-------+--------------+
If you want to filter your table based on a comma separated list with ID, my approach is to
append extra commas at the beginning and at the end of a list as well as at the beginning and at the end of an ID, eg.
1 becomes ,1, and list would become ,1,2,3,4,. The reason for that is to avoid ambigious matches like 1 matches 21 or 12 in a list.
Also, EXISTS is well-suited in that situation, which together with INSTR function should work:
SELECT SUM(`marks`)
FROM `student_mark` sm
WHERE EXISTS(SELECT 1 FROM `class_table`
WHERE `teac_id` = '1' AND
INSTR(CONCAT(',', student_id, ','), CONCAT(',', sm.student_id, ',')) > 0)
Demo
BUT you shouldn't store related IDs in one cell as comma separated list - it should be foreign key column to form proper relation. Joins would become trivial then.
I am not very good at sql but I am getting there. I have searched stackoverflow but I can't seem to find the solution and I hope someone out there can help me. I have a table (users) with data like the following. The book_id column is a key to another table that contains a book the user is subscribed to.
|--------|---------------------|------------------|
| id | book_id | name |
|--------|---------------------|------------------|
| 1 | 1 | jim |
| 2 | 1 | joyce |
| 3 | 1 | mike |
| 4 | 1 | eleven |
| 5 | 2 | max |
| 6 | 2 | dustin |
| 7 | 2 | lucas |
|--------|---------------------|------------------|
I have a function in my PHP code that returns two random users from a specific book id (either 1 or 2). Query one returns the result in column 1 and result two returns the results in column 2 like:
|---------------------|------------------|
| 1 | 2 |
|---------------------|------------------|
| jim | max |
| joyce | dustin |
|---------------------|------------------|
I have achieved this by running two separate queries as seen below. I want to know if it's possible to achieve this functionality with one query and how.
$random_users_with_book_id_1 = SELECT name FROM users WHERE book_id=1 LIMIT 2
$random_users_with_book_id_2 = SELECT name FROM users WHERE book_id=2 LIMIT 2
Again, I apologise if it's too specific. The query below has been closest to what I was trying to achieve.:
SELECT a.name AS book_id_1, b.name AS book_id_2
FROM users a, users b
WHERE a.book_id=1 AND b.book_id = 2
LIMIT 2
EDIT: I have created a fiddle to play around with his. I appreciate any help! Thank you!! http://sqlfiddle.com/#!9/7fcbca/1
It is easy actually :)
you can use UNION like this:
SELECT * FROM (
(SELECT * FROM user WHERE n_id=1 LIMIT 2)
UNION
(SELECT * FROM user WHERE n_id=2 LIMIT 2))
collection;
if you read this article about the documentation you can use the () to group the individual queries and the apply the union in the middle. Without the parenthesis it would still LIMIT 2 and show only the two first. Ref. "To apply ORDER BY or LIMIT to an individual SELECT, place the clause inside the parentheses that enclose the SELECT:"
If you want to combine the queries in MySQL, you can just use parentheses:
(SELECT name
FROM users
WHERE n_id = 1
LIMIT 2
) UNION ALL
(SELECT name
FROM users
WHERE n_id = 2
LIMIT 2
);
First, only use UNION if you specifically want to incur the overhead of removing duplicates. Otherwise, use UNION ALL.
Second, this does not return random rows. This returns arbitrary rows. In many cases, this might be two rows near the beginning of the data. If you want random rows, then use ORDER BY rand():
(SELECT name
FROM users
WHERE n_id = 1
ORDER by rand()
LIMIT 2
) UNION ALL
(SELECT name
FROM users
WHERE n_id = 2
ORDER BY rand()
LIMIT 2
);
There are other methods that are more efficient, but this should be fine for up to a few thousand rows.
Suppose we have a table like the one below.
Id | Name | Group
-----------------
1 | John | 1
2 | Zayn | 2
3 | Four | 2
4 | Ben_ | 3
5 | Joe_ | 2
6 | Anna | 1
The query below will select all of them.
SELECT `Name` FROM `Table` WHERE 1;
How would I select only one person from each group? Who it is doesn't really matter, as long as there's only one name from group 1 and one name from group 2 etc.
The GROUP BY clause isn't fit for this (according to my error console) because I am selecting non aggregated values, which makes sense.
The DISTINCT clause isn't great here either, since I don't want to select the "Group" and definitely not group by their names.
If is not important the resulting name You can anawy leverage some group functions eg with max or min..
leverage the group functions
select max(name) from your_table
group by Group;
otherwise you can use subquery
select name from your_table
where Id in (select min(Id) from your_table group by Group);
I have a table like this:
Table: p
+----------------+
| id | w_id |
+---------+------+
| 5 | 8 |
| 5 | 10 |
| 5 | 8 |
| 5 | 10 |
| 5 | 8 |
| 6 | 5 |
| 6 | 8 |
| 6 | 10 |
| 6 | 10 |
| 7 | 8 |
| 7 | 10 |
+----------------+
What is the best SQL to get the following result? :
+-----------------------------+
| id | most_used_w_id |
+---------+-------------------+
| 5 | 8 |
| 6 | 10 |
| 7 | 8 |
+-----------------------------+
In other words, to get, per id, the most frequent related w_id.
Note that on the example above, id 7 is related to 8 once and to 10 once.
So, either (7, 8) or (7, 10) will do as result. If it is not possible to
pick up one, then both (7, 8) and (7, 10) on result set will be ok.
I have come up with something like:
select counters2.p_id as id, counters2.w_id as most_used_w_id
from (
select p.id as p_id,
w_id,
count(w_id) as count_of_w_ids
from p
group by id, w_id
) as counters2
join (
select p_id, max(count_of_w_ids) as max_counter_for_w_ids
from (
select p.id as p_id,
w_id,
count(w_id) as count_of_w_ids
from p
group by id, w_id
) as counters
group by p_id
) as p_max
on p_max.p_id = counters2.p_id
and p_max.max_counter_for_w_ids = counters2.count_of_w_ids
;
but I am not sure at all whether this is the best way to do it. And I had to repeat the same sub-query two times.
Any better solution?
Try to use User defined variables
select id,w_id
FROM
( select T.*,
if(#id<>id,1,0) as row,
#id:=id FROM
(
select id,W_id, Count(*) as cnt FROM p Group by ID,W_id
) as T,(SELECT #id:=0) as T1
ORDER BY id,cnt DESC
) as T2
WHERE Row=1
SQLFiddle demo
Formal SQL
In fact - your solution is correct in terms of normal SQL. Why? Because you have to stick with joining values from original data to grouped data. Thus, your query can not be simplified. MySQL allows to mix non-group columns and group function, but that's totally unreliable, so I will not recommend you to rely on that effect.
MySQL
Since you're using MySQL, you can use variables. I'm not a big fan of them, but for your case they may be used to simplify things:
SELECT
c.*,
IF(#id!=id, #i:=1, #i:=#i+1) AS num,
#id:=id AS gid
FROM
(SELECT id, w_id, COUNT(w_id) AS w_count
FROM t
GROUP BY id, w_id
ORDER BY id DESC, w_count DESC) AS c
CROSS JOIN (SELECT #i:=-1, #id:=-1) AS init
HAVING
num=1;
So for your data result will look like:
+------+------+---------+------+------+
| id | w_id | w_count | num | gid |
+------+------+---------+------+------+
| 7 | 8 | 1 | 1 | 7 |
| 6 | 10 | 2 | 1 | 6 |
| 5 | 8 | 3 | 1 | 5 |
+------+------+---------+------+------+
Thus, you've found your id and corresponding w_id. The idea is - to count rows and enumerate them, paying attention to the fact, that we're ordering them in subquery. So we need only first row (because it will represent data with highest count).
This may be replaced with single GROUP BY id - but, again, server is free to choose any row in that case (it will work because it will take first row, but documentation says nothing about that for common case).
One little nice thing about this is - you can select, for example, 2-nd by frequency or 3-rd, it's very flexible.
Performance
To increase performance, you can create index on (id, w_id) - obviously, it will be used for ordering and grouping records. But variables and HAVING, however, will produce line-by-line scan for set, derived by internal GROUP BY. It isn't such bad as it was with full scan of original data, but still it isn't good thing about doing this with variables. On the other hand, doing that with JOIN & subquery like in your query won't be much different, because of creating temporery table for subquery result set too.
But to be certain, you'll have to test. And keep in mind - you already have valid solution, which, by the way, isn't bound to DBMS-specific stuff and is good in terms of common SQL.
Try this query
select p_id, ccc , w_id from
(
select p.id as p_id,
w_id, count(w_id) ccc
from p
group by id,w_id order by id,ccc desc) xxx
group by p_id having max(ccc)
here is the sqlfidddle link
You can also use this code if you do not want to rely on the first record of non-grouping columns
select p_id, ccc , w_id from
(
select p.id as p_id,
w_id, count(w_id) ccc
from p
group by id,w_id order by id,ccc desc) xxx
group by p_id having ccc=max(ccc);
Alright so I have a table, in this table are two columns with ID's. I want to make one of the columns distinct, and once it is distinct to select all of those from the second column of a certain ID.
Originally I tried:
select distinct inp_kll_id from kb3_inv_plt where inp_plt_id = 581;
However this does the where clause first, and then returns distinct values.
Alternatively:
select * from (select distinct(inp_kll_id) from kb3_inv_plt) as inp_kll_id where inp_plt_id = 581;
However this cannot find the column inp_plt_id because distinct only returns the column, not the whole table.
Any suggestions?
Edit:
Each kll_id may have one or more plt_id. I would like unique kll_id's for a certain kb3_inv_plt id.
| inp_kll_id | inp_plt_id |
| 1941 | 41383 |
| 1942 | 41276 |
| 1942 | 38005 |
| 1942 | 39052 |
| 1942 | 40611 |
| 1943 | 5868 |
| 1943 | 4914 |
| 1943 | 39511 |
| 1944 | 39511 |
| 1944 | 41276 |
| 1944 | 40593 |
| 1944 | 26555 |
If you do mean, by "make distinct", "pick only inp_kll_ids that happen just once" (not the SQL semantics for Distinct), this should work:
select inp_kll_id
from kb3_inv_plt
group by inp_kll_id
having count(*)=1 and inp_plt_id = 581;
Get all the distinct first (alias 'a' in my following example) and then join it back to the table with the specified criteria (alias 'b' in my following example).
SELECT *
FROM (
SELECT
DISTINCT inp_kll_id
FROM kb3_inv_plt
) a
LEFT JOIN kb3_inv_plt b
ON a.inp_kll_id = b.inp_kll_id
WHERE b.inp_plt_id = 581
in this table are two columns with
ID's. I want to make one of the
columns distinct, and once it is
distinct to select all of those from
the second column of a certain ID.
SELECT distinct tableX.ID2
FROM tableX
WHERE tableX.ID1 = 581
I think your understanding of distinct may be different from how it works. This will indeed apply the where clause first, and then get a distinct list of unique entries of tableX.ID2, which is exactly what you ask for in the first part of your question.
By making a row distinct, you're ensuring no other rows are exactly the same. You aren't making a column distinct. Let's say your table has this data:
ID1 ID2
10 4
10 3
10 7
4 6
When you select distinct ID1,ID2 - you get the same as select * because the rows are already distinct.
Can you add information to clear up what you are trying to do?