How do you get the median of a row in MySQL?
I have a table which gives monthly stock for a series of categories:
cat_id | mar_stk | feb_stk | jan_stk
1 | 5 | 7 | 9
2 | 2 | 1 | 3
3 | 6 | 8 | 10
I need the median, maximum and minimum stock for each category.
Currently have minimum and maximum using:
SELECT
cat_id,
GREATEST(mar_stk, feb_stk, jan_stk) AS max_stk,
LEAST(mar_stk, feb_stk, jan_stk) AS min_stk
FROM example_table
Which leaves me with:
cat_id | max_stk | min_stk
1 | 9 | 5
2 | 3 | 1
3 | 10 | 6
But I can't find any straightforward way to find the median.
By statistics, Median is the middle number in a given out distribution. For instance if in the column cat_id where you have value 1,2,3 etc. Your median is 2 since its the number or value at the middle. Query the middle value and then hurray. Give me a shout if you still need further guide. ..Sectona
Related
For example, there are three rooms.
1|gold_room|1,2,3
2|silver_room|1,2,3
3|brown_room|2,4,6
4|brown_room|3
5|gold_room|4,5,6
Then, I'd like to get
gold_room|1,2,3,4,5,6
brown_room|2,3,4,6
silver_room|1,2,3
How can I achieve this?
I've tried: select * from room group by name; And it only prints the first row. And I know CONCAT() can combine two string values.
Please use below query,
select col2, GROUP_CONCAT(col3) from data group by col2;
Below is the Test case,
https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=ab35e8d66ffe3ac6436c17faf97ee9af
I'm not making an assumption that the lists don't have elements in common on separate rows.
First create a table of integers.
mysql> create table n (n int primary key);
mysql> insert into n values (1),(2),(3),(4),(5),(6);
You can join this to your rooms table using the FIND_IN_SET() function. Note that this cannot be optimized. It will execute N full table scans. But it does create an interim set of rows.
mysql> select * from n inner join rooms on find_in_set(n.n, rooms.csv) order by rooms.room, n.n;
+---+----+-------------+-------+
| n | id | room | csv |
+---+----+-------------+-------+
| 2 | 3 | brown_room | 2,4,6 |
| 3 | 4 | brown_room | 3 |
| 4 | 3 | brown_room | 2,4,6 |
| 6 | 3 | brown_room | 2,4,6 |
| 1 | 1 | gold_room | 1,2,3 |
| 2 | 1 | gold_room | 1,2,3 |
| 3 | 1 | gold_room | 1,2,3 |
| 4 | 5 | gold_room | 4,5,6 |
| 5 | 5 | gold_room | 4,5,6 |
| 6 | 5 | gold_room | 4,5,6 |
| 1 | 2 | silver_room | 1,2,3 |
| 2 | 2 | silver_room | 1,2,3 |
| 3 | 2 | silver_room | 1,2,3 |
+---+----+-------------+-------+
Use GROUP BY to reduce these rows to one row per room. Use GROUP_CONCAT() to put the integers together into a comma-separated list.
mysql> select room, group_concat(distinct n.n order by n.n) as csv
from n inner join rooms on find_in_set(n.n, rooms.csv) group by rooms.room
+-------------+-------------+
| room | csv |
+-------------+-------------+
| brown_room | 2,3,4,6 |
| gold_room | 1,2,3,4,5,6 |
| silver_room | 1,2,3 |
+-------------+-------------+
I think this is a lot of work, and impossible to optimize. I don't recommend it.
The problem is that you are storing comma-separated lists of numbers, and then you want to query it as if the elements in the list are discrete values. This is a problem for SQL.
It would be much better if you did not store your numbers in a comma-separated list. Store multiple rows per room, with one number per row. You can run a wider variety of queries if you do this, and it will be more flexible.
For example, the query you asked about, to produce a result with numbers in a comma-separated list is more simple, and you don't need the extra n table:
select room, group_concat(n order by n) as csv from rooms group by room
See also my answer to Is storing a delimited list in a database column really that bad?
I need to skip results with high price per day. I've got a table like this:
+------+-------------+-------+
| days | return_date | value |
+------+-------------+-------+
| 2 | 2017-12-27 | 15180 |
| 3 | 2017-12-28 | 14449 |
| 4 | 2017-12-29 | 13081 |
| 5 | 2017-12-30 | 11203 |
| 6 | 2017-12-31 | 9497 |
| 6 | 2017-12-31 | 9442 |
+------+-------------+-------+
How can I print only the lowest price for 6 days (9442 in this example).
We can use a GROUP BY clause and an aggregate function. For example:
SELECT t.days
, t.return_date
, MIN(t.value) AS min_value
FROM mytable t
GROUP
BY t.days
, t.return_date
This doesn't really "skip" rows. It accesses all the rows that satisfy the conditions in the WHERE clause (in this example, every row in the table). Then MySQL collapses rows into groups (in this example, rows with identical values of days and return_date get put into a group. The MIN(t.value) aggregate function selects out the minimum (lowest) value out of the group.
The query above is just an example of one approach of satisfying a particular specification.
Is it possible to select random rows from a table whose particular column total (sum) should be less than my condition value ?
My table structure is like -
id | question | answerInSec
1 | Quest1 | 15
2 | Quest2 | 20
3 | Quest3 | 10
4 | Quest4 | 15
5 | Quest5 | 10
6 | Quest6 | 15
7 | Quest7 | 20
I want to get those random questions whose total sum of 'answerInSec' column is less than (nearest total) or equal to 60.
So random combination can be [1,2,3,4] OR [2,3,5,7] OR [4,5,6,7] etc.
Is this possible in single MySQL query ?
Are you look for this :
SELECT * FROM tbl_name ORDER BY RAND() WHERE [condition] LIMIT 10
I've checked out a few of the stackoverflow questions and there are similar questions, but didn't quite put my fingers on this one.
If you have a table like this:
uid cat_uid itm_uid
1 1 4
2 1 5
3 2 6
4 2 7
5 3 8
6 3 9
where the uid column in auto_incremented and the cat_uid references a
category of relevance to filter on and the itm_uid values are the one
we're seeking
I would like to get a result set that contains the following sample results:
array (
0 => array (1 => array(4,5)),
1 => array (2 => array(6,7)),
2 => array (3 => array(8,9))
)
An example issue is - select 2 records from each category (however many categories there may be) and make sure they are the last 2 entries by uid in those categories.
I'm not sure how to structure the question to allow an answer, and any hints on a method for the solution would be welcome!
EDIT:
This wasn't a very clear question, so let me extend the scenario to something more tangible.
I have a set of records being entered into categories and I would like to select, with as few queries as possible, the latest 2 records entered per category, so that when I list out the contents of those categories, I will have at least 2 records per category (assuming that there are 2 or more already in the database). A similar query was in place that selected the last 100 records and filtered them into categories, but for small numbers of categories with some being updated faster than others can lead to having the top 100 not consisting of members from every category, so to try to resolve that, I was looking for a way to select 2 records from each category (or N-records assuming it's the same per-category) and for those 2 records to be the last entered. A date field is available to sort on, but the itm_uid itself could be used to indicate inserted order.
SELECT cat_uid, itm_uid,
IF( #cat = cat_uid, #cat_row := #cat_row + 1, #cat_row := 0 ) AS cat_row,
#cat := cat_uid
FROM my_table
JOIN (SELECT #cat_row := 0, #cat := 0) AS init
HAVING cat_row < 2
ORDER BY cat_uid, uid DESC
You will have two extra columns in the results, just ignore them.
This is the logic:
We sort the table by cat_uid, uid descending, then we start from the top and give each row a "row number" (cat_row) we reset this row number to zero whenever cat_uid changes:
---------------------------------------
| uid | cat_uid | itm_uid | cat_row |
| 45 | 4 | 34 | 0 |
| 33 | 4 | 54 | 1 |
| 31 | 4 | 12 | 2 |
| 12 | 4 | 51 | 3 |
| 56 | 6 | 11 | 0 |
| 20 | 6 | 64 | 1 |
| 16 | 6 | 76 | 2 |
| ... | ... | ... | ... |
---------------------------------------
now if we keep only the rows that have cat_row < 2 we get the results we want:
---------------------------------------
| uid | cat_uid | itm_uid | cat_row |
| 45 | 4 | 34 | 0 |
| 33 | 4 | 54 | 1 |
| 56 | 6 | 11 | 0 |
| 20 | 6 | 64 | 1 |
| ... | ... | ... | ... |
---------------------------------------
This is called an adjacent tree model or a parent-child tree model. It's one of the simplier tree model where there is only 1 pointer or 1 leaf. You would solve your query with a recursion or using a Self Join. Sadly MySQL doesn't support recursive queries, maybe it's working with prepared statements. I want to suggest you an Self Join. With a Self Join you can get all the rows from the right side and the left side with a special condition.
select t1.cat_uid, t2.cat_uid, t1.itm_uid, t2.itm_uid From t1 Inner Join t2 On t1.cat_uid = t2.cat_uid
First off, I apologize for the length. This is kind of complicated (at least for me).
Background on the database:
I have a products, variables, and prices table. "Products" are the main information regarding a product (description, title, etc). "Prices" have information about each price (price, cost, minimum qty required, shipping cost, etc), as some products can have more than one price (a 10" widget is a different price than a 12" widget, for instance). "Variables" are variations to the product that do not change the price, such as color, size, etc.
Initially (when I built this database about 7 years ago) I had the variable information stored in the first price in a list of prices for the same product in a pipe-delimited format (yes, I know, badbadbad). This worked in general, but we've always had a problem, though, where sometimes a variable wouldn't be consistent among all the prices.
For instance, a Widget (product) may be 10" or 12" and sell for $10 and $20 (prices) respectively. However, while the 10" widget may be available in blue and red (variables), the 12" widget is only available in red. We ameliorated this problem by adding a little parenthetical statement in the incongruent variable like "Red (10" ONLY)". This sort of works, but customers are not always that smart and a lot of time is devoted to fixing mistakes when a customer selects a 12" widget in red.
I have since been tasked with modernizing the database and have decided to put the variables in their own table and making them more dynamic and easier to match with certain prices, as well as keep a more dummy-proof inventory (you can't imagine the nightmares).
My first step was to write a stored procedure on my test db (for when I do the conversion) to process all the existing variables into a new variable table (and label table, but that's not really important, I don't think). I effectively parsed out the variables and listed them with the correct product id and the product id they were initially associated with in the variable table. However, I realized this is only a part of the problem, since I (at least for the initial transformation of the database) want each variable to be listed as being connected to each price for a given product.
To do this, I created another table, like so:
tblvariablesprices
variablepriceid | variableid | priceid | productid
which is a many-to-many with the variable table.
Problems:
My problem now is, I don't know how to create the rows. I can create a left join on my prices and variables tables to get (I think) all the necessary data, I just don't know how to go through it. My sql is (mysql 5.0):
SELECT p.priceid, p.productid, variableid, labelid
FROM tblprices p
LEFT JOIN tblvariables v ON p.priceid = v.priceid
ORDER BY productid, priceid
This will get me every priceid and productid and any matching variable and label ids. This is good in certain instances, such as when I have something like:
priceid | productid | variableid | labelid
2 | 7 | 10 | 4
2 | 7 | 11 | 4
2 | 7 | 12 | 4
3 | 7 | (null) | (null) --- another price for product
because now I know that I need to create a record for priceid 2 and variableids 10, 11, 12, and then also for priceid 3 for that product. However, I also get results from this dataset for products with no variables, products with one price and multiple variables, and products with multiple prices and no variables, for instance:
priceid | productid | variableid | labelid
2 | 7 | 10 | 4
2 | 7 | 11 | 4
2 | 7 | 12 | 4
3 | 7 | (null) | (null)
4 | 8 | (null) | (null) --- 1 price no variables
5 | 9 | 13 | 5 --- mult vars, 1 price
5 | 9 | 14 | 5
5 | 9 | 15 | 6
5 | 9 | 16 | 6
6 | 10 | (null) | (null) --- mult price, no vars
7 | 10 | (null) | (null)
8 | 10 | (null) | (null)
Taking the above dataset, I want to add entries into my tblpricesvariables table like so:
variablepriceid | variableid | priceid | productid
1 | 10 | 2 | 7
2 | 11 | 2 | 7
3 | 12 | 2 | 7
4 | 10 | 3 | 7
5 | 11 | 3 | 7
6 | 12 | 3 | 7
7 | 13 | 5 | 9
8 | 14 | 5 | 9
9 | 15 | 5 | 9
10 | 16 | 5 | 9
I have thousands of records to process, so obviously doing this manually is not the answer. Can anyone at least point me in the correct direction, if not come up with a sproc that could handle this type of operation? I also would welcome any comments on how to better organize and/or structure this data.
Thank you so much for reading all this and helping me out.
How about:
SELECT DISTINCT b.variableid, a.priceid, a.productid
FROM tblprices AS a
JOIN tblprices AS b ON a.productid = b.productid
WHERE b.labelid IS NOT NULL
ORDER BY priceid;
+------------+---------+-----------+
| variableid | priceid | productid |
+------------+---------+-----------+
| 10 | 2 | 7 |
| 11 | 2 | 7 |
| 12 | 2 | 7 |
| 10 | 3 | 7 |
| 11 | 3 | 7 |
| 12 | 3 | 7 |
| 13 | 5 | 9 |
| 14 | 5 | 9 |
| 15 | 5 | 9 |
| 16 | 5 | 9 |
+------------+---------+-----------+
INSERTing into tblvariables is left as an exercise for the reader ;)
I think this should work:
SELECT v.variableid, p.productid, p.priceid
FROM tblvariables v, tblprices p
WHERE v.priceid IN (SELECT s.priceid
FROM tblprices s
WHERE s.productid = p.productid);
Next time, can you throw in create and insert statements to replicate your setup? Thanks.