I have the following table (points):
recno uid uname points
============================
1 a abc 10
2 b bac 8
3 c cvb 12
4 d aty 13
5 f cyu 9
-------------------------
--------------------------
What I need is to show only the top ten records with by points (desc) and five records on each page. I have following the SQL statement:
select * from points where uid in(a,c) order by uid LIMIT 1, 5
Thanks
for the first page:
SELECT * FROM points p ORDER BY points DESC LIMIT 0, 5
for the second page:
SELECT * FROM points p ORDER BY points DESC LIMIT 5, 5
You can't execute an SQL query to return a set number of pages, you'll have to implement some kind of pagination module or whatever equivalent there is for the scenario you're in and fetch LIMIT 0, 5 for one then LIMIT 5, 5 for the other.
With such few records it wouldn't be an issue but in a production scale environment selected all records then breaking those results down into pages would be a lot of unnecessary overhead, it's good practice to only select the data you need.
Related
I have been at this for a few days without much luck and I am looking for some guidance on how to get the lowest estimate from a particular group of sullpiers and then place it into another table.
I have 4 supplier estimate on every piece of work and all new estimates go into a single table, i am trying to find the lowest 'mid' price from the 4 newsest entries in the 'RECENT QUOTE TABLE' with a group id of '1' and then place that into the 'LOWEST QUOTE TABLE' as seen below.
RECENT QUOTE TABLE:
suppid group min mid high
1 1 200 400 600
2 1 300 500 700
3 1 100 300 500
[4] [1] 50 [150] 300
5 2 1000 3000 5000
6 2 3000 5000 8000
7 2 2000 4000 6000
8 2 1250 3125 5578
LOWEST QUOTE TABLE:
suppid group min mid high
4 1 50 150 300
Any help on how to structure this would be great as i have been loking for a few days and have not been able to find anything to get me moving again, im using MYSQL and the app is made in Python im open to all suggestions.
Thanks in advance.
If you really want to select only row with group 1, you can do something like
INSERT INTO lowest_quote_table
SELECT * FROM recent_quote_table
WHERE `group` = 1
ORDER BY `mid` ASC
LIMIT 1.
If you want a row with the lowest mid from every group, you can do something like
INSERT INTO lowest_quote_table
SELECT rq.* FROM recent_quote_table AS rq
JOIN (
SELECT `group`, MIN(`mid`) AS min_mid FROM recent_quote_table
GROUP BY `group`
) MQ ON rq.`group` = MQ.`group` AND rq.`mid` = MQ.min_mid
I have a table users and some other tables like images and products
Table users:
user_id user_name
1 andrew
2 lutz
3 sophie
4 michael
5 peter
6 oscor
7 anton
8 billy
9 henry
10 jon
Tables images:
user_id img_type img_url
1 0 url1
1 1 url4
2 0 url5
7 0 url7
8 0 url8
9 1 url9
Table Products
user_id prod_id
1 5
1 55
2 555
8 5555
9 5
9 55
I use this kind of SELECT:
SELECT * FROM
(SELECT user.user_id,user.user_name, img.img_type, prod.prod_id FROM
users
LEFT JOIN images img ON img.user_id = users.user_id
LEFT JOIN products prod ON prod.user_id = users.user_id
WHERE user.user_id <= 5) AS users
ORDER BY user.user_id ASC
The result should be the following output. Due to performance improvements, I use ORDER BY and an inner select. If I put a LIMIT 5 within the inner or outer select, things won't work. MySQL will hard LIMIT the results to 5. However I need the LIMIT of 5 (pagination) found unique user_id results which would lead to 9 in this case.
Can I use maybe an if-statement to push an array with found user_id and break/finish up the select when the array consist of 5 UIDs? Or can I modify somehow the select?
user_id user_name img_type prod_id
1 andrew 0 5
1 andrew 1 5
1 andrew 0 55
1 andrew 1 55
2 lutz 0 5
2 lutz 0 55
3 sophie null null
4 michael null null
5 peter null null
results: 9
LIMIT 5 and user_id <= 5 do not necessarily give you the same results. One reason: There are multiple rows (after the JOINs) for user_id = 1. This is because there can be multiple images and/or multiple products for a given 'user'.
So, first decide which you want.
LIMIT without ORDER BY gives you an arbitrary set of rows. (Yeah, it is somewhat predictable, but you should not depend on it.)
ORDER BY + LIMIT usually implies gathering all the potentially relevant rows, sorting them, then doing the "limit". There are sometimes ways around this sluggishness.
LEFT leads to the NULLs you got; did you want that?
What do you want pagination to do if you are displaying 5 items per page, but user 1 has 6 images? You need to think about this edge case before we can help you with a solution. Maybe you want all of user 1 on a page, even if it exceeds 5? Maybe you want to break in the middle of '1'; but then we need an unambiguous way to know where to continue from for the next page.
Probably any viable solution will not use nested SELECTs. As you are finding out, it leads to "errors". Think of it this way: First find all the rows you need to display on all the pages, then carve out 5 for the current page.
Here are some more musings on pagination: http://mysql.rjweb.org/doc.php/pagination
I have 1 table from which I return search results and display them in a a specific order. This example is an exact, simplified version of my db structure: http://www.java2s.com/Code/SQL/Select-Clause/Orderbyvaluefromsubquery.htm
and here is my current code, which works but heavily impacts performance to a large extend because of the subquery used:
SELECT * FROM `table` AS p1
WHERE CONCAT(title,artist,creator,version) LIKE '%searchInput%'
ORDER BY
(SELECT
MAX(`rating`) FROM `table` AS p2 WHERE p1.setId=p2.setId
) DESC
the above code searches and sorts the result sets by the highest rating in the set and that all rows from the same set are kept together, for example:
id setId rating title,artist,etc...
1 1 5
2 1 5
3 2 7
4 1 6
5 2 1
6 3 3
would sort to:
id setId rating title,artist,etc...
3 2 7
5 2 1
4 1 6
1 1 5
2 1 5
6 3 3
Currently it takes around 8.5sec to query 1000 rows and over half a minute for a large amount of rows, is there any way to improve the performance or would it be better to fetch all the results and sort them in PHP memory?
Help is much appreciated
You can probably speed things up a bit by separating the LIKEs:
SELECT p1.* FROM `table` AS p1
WHERE (title LIKE '%searchInput%')
OR (artist LIKE '%searchInput%')
OR (creator LIKE '%searchInput%')
OR (version LIKE '%searchInput%')
ORDER BY
(SELECT MAX(`rating`) FROM `table` AS p2 WHERE p1.setId=p2.setId) DESC
You could also try to
CREATE INDEX tbl_ndx ON table(setId, rating)
to improve sorting performances.
If I want in MySQL rows 1 through 500, should I use LIMIT 0, 500 or LIMIT, 1, 500? What is the difference? Thanks!
The first one starts from the first record of the whole result, while the second one starts on the second record of the result.
Consider the following records
ID
1 -- index of the first record is zero.
2
3
4
5
6
if you execute
LIMIT 0, 3
-- the result will be ID: 1,2,3
LIMIT 1, 3
-- the result will be ID: 2,3,4
SQLFiddle Demo
OTHER(s)
Limit - MySQL Command (for more info)
In MySQL, the meaning of LIMIT n1, n2 is :
n1 : starting index
n2 : number of record/data you want to show
For example :
ID
-------------------------
1 ------------ > index 0
2
3
4
5
6
7
8
9
10 ------------ > index 9
Now if you write query like
SELECT * from tbl_name LIMIT 0,5
Output :
1
2
3
4
5
And if you write query like
SELECT * from tbl_name LIMIT 2,7
Output :
3
4
5
6
7
8
9
#JohnWoo That's not correct. The order of rows from a SELECT statement, with no ORDER BY clause, is unspecified. Therefore even though by visually looking at the output order of such a query it may seem to be in a specific order, that order is not guaranteed and therefore not reliable. If you require a result set to be ordered in a certain way you must use an ORDER BY clause.
ID
1
2
3
4
5 ------------ > index 0
6
7
8
9 ------------ > after 5 index add 4 value
10
If you want data from 5 to 9 so query should be
SELECT * from table_name LIMIT 5,4
I need help with a MySQL query. We have a database (~10K rows) which I have simplified down to this problem.
We have 7 truck drivers who visit 3 out of a possible 9 locations, daily. Each day they visit exactly 3 different locations and each day they can visit different locations than the previous day. Here are representative tables:
Table: Drivers
id name
10 Abe
11 Bob
12 Cal
13 Deb
14 Eve
15 Fab
16 Guy
Table: Locations
id day address driver.id
1 1 Oak 10
2 1 Elm 10
3 1 4th 10
4 1 Oak 16
5 1 4th 16
6 1 Toy 16
7 1 Toy 11
8 1 5th 11
9 1 Law 11
10 2 Oak 11
11 2 4th 11
12 2 Toy 11
.........
We have data for a full year and we need to find out how many times each "route" is visited over a year, sorted from most to least.
From my high school math, I believe there are 9!/(6!3!) route combinations, or 84 in total. I want do something like:
Get count of routes where route addresses = 'Oak' and 'Elm' and '4th'
then run again
where route addresses = 'Oak' and 'Elm' and '5th'
then again and again, etc.Then sort the route counts, descending. But I don't want to do it 84 times. Is there a way to do this?
I'd be looking at GROUP_CONCAT
SELECT t.day
, t.driver
, GROUP_CONCAT(t.address ORDER BY t.address)
FROM mytable t
GROUP
BY t.day
, t.driver
What's not clear here, if there's an order to the stops on the route. Does the sequence make a difference, and how to we tell what the sequence is? To ask that a different way, consider these two routes:
('Oak','Elm','4th') and ('Elm','4th','Oak')
Are these equivalent (because it's the same set of stops) or are they different (because they are in a different sequence)?
If sequence of stops on the route distinguishes it from other routes with the same stops (in a different order), then replace the ORDER BY t.address with ORDER BY t.id or whatever expression gives the sequence of the stops.
Some caveats with GROUP_CONCAT: the maximum length is limited by the setting of group_concat_max_len and max_allowed_packet variables. Also, the comma used as the separator... if we combine strings that contain commas, then in our result, we can't reliably distinguish between 'a,b'+'c' and 'a'+'b,c'
We can use that query as an inline view, and get a count of the the number of rows with identical routes:
SELECT c.route
, COUNT(*) AS cnt
FROM ( SELECT t.day
, t.driver
, GROUP_CONCAT(t.address ORDER BY t.address) AS route
FROM mytable t
GROUP
BY t.day
, t.driver
) c
GROUP
BY c.route
ORDER
BY cnt DESC