I have a table that looks like:
ID | TICKET PRICE | VIP
----------------------------
1 | $45.00 | 1
2 | $40.00 | 1
3 | $20.00 | 0
4 | $65.00 | 0
5 | $45.00 | 1
I need to query this table to order all rows by Price, but always show one random row which has a VIP=1 at the top. So for example, the query should return:
ID | TICKET PRICE | VIP
----------------------------
2 | $40.00 | 1
3 | $20.00 | 0
1 | $45.00 | 1
5 | $45.00 | 1
4 | $65.00 | 0
And when you refresh the page, row ID 5 may then become the first row, because it has a VIP=1.
I currently have my query looking like:
(SELECT * FROM tickets WHERE VIP=1 ORDER BY rand() LIMIT 1)
UNION
(SELECT * FROM tickets WHERE VIP=0 ORDER BY ticket_price ASC)
This issue with this is that it will only display one VIP row. How would I query this data properly?
Use order by. Here is one method:
select t.*
from (select t.*, (#rn := #rn + 1) as seqnum
from tickets t cross join
(select #rn := 0) params
order by vip desc, rand()
) t
order by (seqnum = 1) desc, price asc;
This uses the subquery to identify the one row to keep at the top. Then it uses this information for ordering in the outer query.
If your rows have a unique identifier, you could also do:
select t.*
from tickets t cross join
(select id from tickets where vip = 1 order by rand() limit 1) as t1
order by (t.id = t1.id) desc, price asc;
Related
Lets say we have a table that looks like this:
+---------------+----------------+-------------------+
| ID | random_string | time |
+---------------+----------------+-------------------+
| 2 | K2K3KD9AJ |2022-07-21 20:41:15|
| 1 | SJQJ8JD0W |2022-07-17 23:46:13|
| 1 | JSDOAJD8 |2022-07-11 02:52:21|
| 3 | KPWJOFPSS |2022-07-11 02:51:57|
| 1 | DA8HWD8HHD |2022-07-11 02:51:49|
------------------------------------------------------
I want to select the last 3 entries into the table, however they must all have separate ID's.
Expected Result:
+---------------+----------------+-------------------+
| ID | random_string | time |
+---------------+----------------+-------------------+
| 2 | K2K3KD9AJ |2022-07-21 20:41:15|
| 1 | SJQJ8JD0W |2022-07-17 23:46:13|
| 3 | KPWJOFPSS |2022-07-11 02:51:57|
------------------------------------------------------
I have already tried:
SELECT DISTINCT id FROM table ORDER BY time DESC LIMIT 3;
And:
SELECT MIN(id) as id FROM table GROUP BY time DESC LIMIT 3;
If you're not on MySQL 8, then I have two suggestions.
Using EXISTS:
SELECT m1.ID,
m1.random_string,
m1.time
FROM mytable m1
WHERE EXISTS
(SELECT ID
FROM mytable AS m2
GROUP BY ID
HAVING m1.ID=m2.ID
AND m1.time= MAX(time)
)
Using JOIN:
SELECT m1.ID,
m1.random_string,
m1.time
FROM mytable m1
JOIN
(SELECT ID, MAX(time) AS mxtime
FROM mytable
GROUP BY ID) AS m2
ON m1.ID=m2.ID
AND m1.time=m2.mxtime
I've not test in large data so don't know which will perform better (speed) however this should return the same result:
Here's a fiddle
Of course, this is considering that there will be no duplicate of exact same ID and time value; which seems to be very unlikely but still it's possible.
Using MySql 8 an easy solution is to assign a row number using a window:
select Id, random_string, time
from (
select *, Row_Number() over(partition by id order by time desc) rn
from t
)t
where rn = 1
order by time desc
limit 3;
See Demo
I have a sports database where I want to sort the data by a custom field ('Rating') and update the field ('Ranking') with the row number.
I have tried the following code to sort the data by my custom field 'Rating'. It works when I sort it by a normal field, but not with a custom/calculated field. When the sorting has been done, I want it to update the field 'Ranking' with the row number.
Ie the fighter with the highest 'Rating' should have the value '1' as 'Ranking.
SELECT id,lastname, wins, Round(((avg(indrating)*13) + (avg(Fightrating)*5) * 20) / 2,2) as Rating,
ROW_NUMBER() OVER (ORDER BY 'Rating' DESC) AS num
from fighters
JOIN fights ON fights.fighter1 = fighters.id
GROUP BY id
The code above isn't sorting the Rating accurately. It sorts by row number, but the highest Rating isn't rated as #1. It seems a bit random.
SQL Fiddle: http://sqlfiddle.com/#!9/aa1fca/1 (This example is correctly sorted, but I want it to update the "Ranking" column by row number - meaning the highest rated fighter (by 'Rating') gets '1' in the Ranking column, the second highest reated fighter gets '2' in the Ranking column etc).
Also I would like to be able to add WHERE clause in the fighters table (where fighters.organization = 'UFC') for example.
First, let's fix your query so it runs on MySQL < 8.0. This requires doing the computing and sorting in a subquery, then using a variable to compute the rank:
select
id,
rating,
#rnk := #rnk + 1 ranking
from
(select #rnk := 0) r
cross join (
select
fighter1 id,
round(((avg(indrating)*13) + (avg(fightrating)*5) * 20) / 2,2) as rating
from fights
group by fighter1
order by rating desc
) x
Now we use the update ... join ... set ... syntax to update the fighters table:
update fighters f
inner join (
select
id,
rating,
#rnk := #rnk + 1 ranking
from
(select #rnk := 0) r
cross join (
select
fighter1 id,
round(((avg(indrating)*13) + (avg(fightrating)*5) * 20) / 2,2) as rating
from fights
group by fighter1
order by rating desc
) x
) y on y.id = f.id
set f.ranking = y.ranking;
Demo in a MySQL 5.6 fiddle based on the fiddle you provided in the comments.
The select query returns:
| id | rating | ranking |
| --- | ------ | ------- |
| 3 | 219.5 | 1 |
| 4 | 213 | 2 |
| 1 | 169.5 | 3 |
| 2 | 156.5 | 4 |
And here is the content of the fighters table after the update:
| id | lastname | ranking |
| --- | ---------- | ------- |
| 1 | Gustafsson | 3 |
| 2 | Cyborg | 4 |
| 3 | Jones | 1 |
| 4 | Sonnen | 2 |
I have a table with IDs from 1 to 8. I want something like this
If i'm on 4, I should get 3,5
If i'm in on 1, I should get 8,2
If in on 8, I should get 7, 1
Basically looping through the table records
This is my current code
-- previous or last, if there is no previous
SELECT *
FROM news
WHERE id < 1 OR id = MAX(id)
ORDER BY id DESC
LIMIT 1
-- next or first, if there is no next
SELECT *
FROM news
WHERE id > 1 OR id = MIN(id)
ORDER BY id ASC
LIMIT 1
But it says Invalid use of group function. Any help?
If id is sequential you can do this:
SQL DEMO
SELECT o.id,
COALESCE(b.id, (SELECT MAX(ID) FROM Table1)) as before_id,
COALESCE(a.id, (SELECT MIN(ID) FROM Table1)) as after_id
FROM Table1 o
LEFT JOIN Table1 b
ON o.id = b.id + 1
LEFT JOIN Table1 a
ON o.id = a.id - 1
ORDER BY o.id
OUTPUT
| id | before_id | after_id |
|----|-----------|----------|
| 1 | 8 | 2 |
| 2 | 1 | 3 |
| 3 | 2 | 4 |
| 4 | 3 | 5 |
| 5 | 4 | 6 |
| 6 | 5 | 7 |
| 7 | 6 | 8 |
| 8 | 7 | 1 |
If ids are not sequential you need use row_number() (mysql ver 8+) or session variables to create a sequence.
I guess that you want to show "prev" and "next" buttons, when the user views a news article. I would get the previous and the next ID in the main query, when you fetch the article data:
select n.*, -- select columns you need
coalesce(
(select max(n1.id) from news n1 where n1.id < n.id ),
(select max(id) from news)
) as prev_id,
coalesce(
(select min(n1.id) from news n1 where n1.id > n.id ),
(select min(id) from news)
) as next_id
from news n
where n.id = ?
db-fiddle demo
Now you can use prev_id and next_id for your buttons, or prefetch the corresponding articles with a simple select * from news where id = ? query.
You can remove the filtering in your approach and add logic to the ORDER BY:
(SELECT n.*
FROM news
ORDER BY (id < 1), id DESC
LIMIT 1
) UNION ALL
(SELECT n.*
FROM news
ORDER BY (id > 1), id ASC
LIMIT 1
) ;
If you want the id values in one row, you can use aggregation:
select coalesce(max(case when id < 1 then id end), max(id)) as prev_id,
coalesce(min(case when id > 1 then id end), min(id)) as next_id
from news n;
In both cases, 1 is a sample id and the "1" can be replaced with any value.
I need to to get the max price of the 33% cheapests products. My idea is like this. Of course, this code is just an example. I need to use subqueries.
select max((select price from products order by preco limit 33% )) as result from products
For example
product_id price
1 10
2 50
3 100
4 400
5 900
6 8999
I need I query that returns 50, since 33% of the rows are 2, and the max value of the 2(33%) of the rows is 50.
In MySQL 8+, you would use window functions:
select avg(precio)
from (select p.*, row_number() over (order by precio) as seqnum,
count(*) over () as cnt
from products p
) p
where seqnum <= 0.33 * cnt;
Obviously there are multiple approaches to this but here is how I would do it.
Simply get a count on the table. This will let me pick the max price of the cheapest 33% of products. Let's say it returned n records. Third of that would be n/3. Here you can either round up or down but needs to be rounded in case of a fraction.
Then my query would be something like SELECT * FROM products ORDER BY price ASC LIMIT 1 OFFSET n/3. This would return me a single record with minimal calculations and look ups on MySQL side.
For MySQL versions under MySQL 8.0 you can use MySQL's user variables to simulate/emulate a ROW_NUMBER()
Query
SELECT
t.product_id
, t.price
, (#ROW_NUMBER := #ROW_NUMBER + 1) AS ROW_NUMBER
FROM
t
CROSS JOIN (SELECT #ROW_NUMBER := 0) AS init_user_variable
ORDER BY
t.price ASC
Result
| product_id | price | ROW_NUMBER |
| ---------- | ----- | ---------- |
| 1 | 10 | 1 |
| 2 | 50 | 2 |
| 3 | 100 | 3 |
| 4 | 400 | 4 |
| 5 | 900 | 5 |
| 6 | 8999 | 6 |
When we get the ROW_NUMBER we can use that in combination with ROW_NUMBER <= CEIL(((SELECT COUNT(*) FROM t) * 0.33));
Which works like this
(SELECT COUNT(*) FROM t) => Counts and returns 6
(SELECT COUNT(*) FROM t) * 0.33) Calculates 33% from 6 which is 1.98 and returns it
CEIL(..) Return the smallest integer value that is greater than or equal to 1.98 which is 2 in this case
ROW_NUMBER <= 2 So the last filter is this.
Query
SELECT
a.product_id
, a.price
FROM (
SELECT
t.product_id
, t.price
, (#ROW_NUMBER := #ROW_NUMBER + 1) AS ROW_NUMBER
FROM
t
CROSS JOIN (SELECT #ROW_NUMBER := 0) AS init_user_variable
ORDER BY
t.price ASC
) AS a
WHERE
ROW_NUMBER <= CEIL(((SELECT COUNT(*) FROM t) * 0.33));
Result
| product_id | price |
| ---------- | ----- |
| 1 | 10 |
| 2 | 50 |
see demo
To get get the max it's just as simple as adding ORDER BY a.price DESC LIMIT 1
Query
SELECT
a.product_id
, a.price
FROM (
SELECT
t.product_id
, t.price
, (#ROW_NUMBER := #ROW_NUMBER + 1) AS ROW_NUMBER
FROM
t
CROSS JOIN (SELECT #ROW_NUMBER := 0) AS init_user_variable
ORDER BY
t.price ASC
) AS a
WHERE
ROW_NUMBER <= CEIL(((SELECT COUNT(*) FROM t) * 0.33))
ORDER BY
a.price DESC
LIMIT 1;
Result
| product_id | price |
| ---------- | ----- |
| 2 | 50 |
see demo
If your version supports window functions, you can use NTILE(3) to divide the rows into three groups ordered by price. The first group will contain (about) "33%" of lowest prices. Then you just need to select the MAX value from that group:
with cte as (
select price, ntile(3) over (order by price) as ntl
from products
)
select max(price)
from cte
where ntl = 1
Demo
Prior to MySQL 8.0 I would use a temprary table with an AUTO_INCREMENT column:
create temporary table tmp (
rn int auto_increment primary key,
price decimal(10,2)
);
insert into tmp(price)
select price from products order by price;
set #max_rn = (select max(rn) from tmp);
select price
from tmp
where rn <= #max_rn / 3
order by rn desc
limit 1;
Demo
As result of mysql query, I have this table:
orders | customer |
1 | A |
1 | A |
1 | B |
1 | B |
1 | B |
Using mysql only, I need to create a column with index oder ocurrence to each customer to get this table:
orders | customer | index
1 | A | 1
1 | A | 2
1 | B | 1
1 | B | 2
1 | B | 3
I try to use this:
set #i=1;
while #i<99999 do
select
count(order_id) as 'orders',
customer_id as 'customer',
#i as 'index'
from
orders
set #i= #i+1;
end while;
But I get an error of statement. Sorry, I have no more idea how to do it. Any idea will be appreciated.
The standard way of doing this with MySQL 8.0 is to use a windowing function:
SELECT orders, customer,
ROW_NUMBER() OVER (PARTITION BY customer) AS `index`
FROM orders
Prior to MySQL 8.0, you can do tricks with inline user variables.
SET #i = 0, #c = '';
SELECT
orders,
IF(#c=customer, #i:=#i+1, #i:=1) AS `index`,
#c:=customer AS customer
FROM orders
ORDER BY customer;
Unfortunately, this needs the customer column to be after the index column.
SELECT
orders.* ,
customerOrderCount ,
IF(#i > 1, #i:= #i - 1, #i:=customerOrdercount) AS orderIndex
FROM (SELECT * FROM orders ORDER BY customer ASC ) AS orders
JOIN (SELECT customer, count(*) AS customerOrderCount FROM orders GROUP BY
customer) counts USING (customer)
ORDER BY customer ASC, orderIndex;