original table
I condensed it with
SELECT type_value, number FROM parts_usage GROUP BY number, type_value
to get result of code
Then i need to add the columns to get 15
When I try to add them it adds all the rows before condensing them down.
Related
Say I have a table with 1million rows. One column lists the "Group", and another lists "Sales". The Group #'s range from 1 to 100,000 such that each Group has about 10 Sales entries. I want to somehow summarize the data into 100,000 rows with the sum of Sales for each group rather than each individual sale.
My method so far has been to run a PHP loop from 1 to 100,000 where each iteration sends an SQL query to sum(Sales) WHERE Group=$i. Then I can either echo it into an html table, or insert it into a new SQL table. Problem is it takes hours this method.
Any tips on how I can improve this process? Is there a way to write this as a single SQL query that will massively increase speed? Thanks
Just try a GROUP BY:
SELECT `group`, sum(sales)
FROM your_table
GROUP BY `group`
Edit to include back ticks for group. Without them you will receive an error
You should always avoid a SQL query in a loop unless there's no other solution. In this case, you can grab all the fields at once and have them in an array and add them up in PHP that way.
How to get duplicate rows containing same string (crn) from a table & crn can contain multiple values too? I got result only for single valued crn.
I wrote a MySQL Query:
SELECT * FROM event_participation
WHERE event_id=15 AND crn IN (SELECT crn FROM event_participation GROUP BY crn HAVING COUNT(*) > 1) ORDER BY crn;
This query can return rows what I expect for but only for single valued crn as shown in second figure.
The first figure shows duplicate rows while fetching all rows from a table but my MySQl query cannot return these duplicate rows containing one of a crn 720286 as in second figure.
Please help me to display those two rows in second figure too.
GitHub Issue: https://github.com/ErSKS/KhEC/issues/10
We have records with a count field on an unique id.
The columns are:
mainId = unique
mainIdCount = 1320 (this 'views' field gets a + 1 when the page is visited)
How can you insert all these mainIdCount's as seperate records in another table IN ANOTHER DBASE in one query?
Yes, I do mean 1320 times an insert with the same mainId! :-)
We actually have records that go over 10,000 times an id. It just has to be like this.
This is a weird one, but we do need the copies of all these (just) counts like this.
The most straightforward way to this is with a JOIN operation between your table, and another row source that provides a set of integers. We'd match each row from our original table to as many rows from the set of integer as needed to satisfy the desired result.
As a brief example of the pattern:
INSERT INTO newtable (mainId,n)
SELECT t.mainId
, r.n
FROM mytable t
JOIN ( SELECT 1 AS n
UNION ALL SELECT 2
UNION ALL SELECT 3
UNION ALL SELECT 4
UNION ALL SELECT 5
) r
WHERE r.n <= t.mainIdCount
If mytable contains row mainId=5 mainIdCount=4, we'd get back rows (5,1),(5,2),(5,3),(5,4)
Obviously, the rowsource r needs to be of sufficient size. The inline view I've demonstrated here would return a maximum of five rows. For larger sets, it would be beneficial to use a table rather than an inline view.
This leads to the followup question, "How do I generate a set of integers in MySQL",
e.g. Generating a range of numbers in MySQL
And getting that done is a bit tedious. We're looking forward to an eventual feature in MySQL that will make it much easier to return a bounded set of integer values; until then, having a pre-populated table is the most efficient approach.
I'm trying to query 2 tables where the first table will return 1 row and the second table will return multiple rows. So basically the first table with return text on a page and the second table will return a list that will go within the page. Both tables have a reference row which is what both tables are queried on. (See Below)
SELECT shop_rigs.*, shop_rigs_images.*, shop_rigs_parts.*
FROM shop_rigs
LEFT JOIN shop_rigs_images
ON shop_rigs.shoprigs_ref = shop_rigs_images.shoprigsimg_ref
LEFT JOIN shop_rigs_parts
ON shop_rigs.shoprigs_ref = shop_rigs_parts.shoprigsparts_ref
WHERE shoprigs_enabled='1' AND shoprigs_ref='$rig_select'
ORDER BY shoprigs_order ASC
Is it better to just do 2 queries?
Thanks,
dane
I would do this in two queries. The problem isn't efficiency or the size of the respective tables, the problem is that you're create a Cartesian product between shop_rigs_images and shop_rigs_parts.
Meaning that if a given row of shop_rigs has three images and four parts, you'll get back 3x4 = 12 rows for that single shop_rig.
So here's how I'd write it:
SELECT ...
FROM shop_rigs
INNER JOIN shop_rigs_images
ON shop_rigs.shoprigs_ref = shop_rigs_images.shoprigsimg_ref
WHERE shoprigs_enabled='1' AND shoprigs_ref='$rig_select'
ORDER BY shoprigs_order ASC
SELECT ...
FROM shop_rigs
INNER JOIN shop_rigs_parts
ON shop_rigs.shoprigs_ref = shop_rigs_parts.shoprigsparts_ref
WHERE shoprigs_enabled='1' AND shoprigs_ref='$rig_select'
ORDER BY shoprigs_order ASC
I left the select-list of columns out, because I agree with #Doug Kress that you should select only the columns you need from a given query, not all columns with *.
If you're pulling a large amount of data from the first table, then it would be better to do two queries.
Also, for efficiency, it would be better to specify each column that you actually need, instead of all columns - that way, less data will be fetched and retrieved.
Joins are usually more efficient than running 2 queries, as long as you are joining on indexes, but then it depends on your data and indexes.
You may want to run a "explain SELECT ....." for both options and compare "possible keys" and "rows" from your results.
SELECT webcal_entry.cal_id, webcal_entry.cal_name , webcal_entry.cal_priority,
webcal_entry.cal_date , webcal_entry.cal_time , webcal_entry_user.cal_status,
webcal_entry.cal_create_by , webcal_entry.cal_access, webcal_entry.cal_duration ,
webcal_entry.cal_description , webcal_entry_user.cal_category
FROM webcal_entry, webcal_entry_user
WHERE webcal_entry.cal_date BETWEEN '20090601' AND '20090631'
When I execute that query php throws back:
mysql_query(): unable to save result set
MySQL client ran out of memory
When I limit the results I see that it is pulling some 2.8 million results back. This table has 7,241 rows.
I realize I could use LIKE, but I really don't want to go that route.
Thanks for any help!
You are joining the webcal_entry and webcal_entry_user tables in your FROM clause but you do not have any JOIN ON or WHERE conditions constraining which rows from webcal_entry_user to return. The result will be the cartesian product of the two tables, which basically means you'll get back each webcal_entry row that has a valid cal_date, multiplied by the number of rows in the webcal_entry_user table.
In other words, if you webcal_entry_user has 400 rows you'll get back 400*7241 = 2.8 million rows! Yikes!
You're doing a cartesian join. Basically, for each row in the first table you're joining against all the rows in the second. If the first table has 4 rows and the second 10 the result set will have 40 (4x10)
You need to add the key you're joining on that exists in both tables to the WHERE clause. Something like:
AND webcal_entry.user_id = webcal_entry_user.user_id