tell some big, diff between order by and group by,
like sort columns data=>order by
group it by similar data used for aggregation , order by could be used inside the grouped items ,
please Tell 5 diff
The order by clause is used to order your data set. For example,
select *
from customers
order by customer_id asc
will give you a list of customers in order of customer id from lowest to highest.
The group by clause is used to aggregate your data. For example,
select customer_id, sum(sale_price), max(sale_price)
from customers
group by customer_id
order by customer_id asc
will give you each customer along with their total sales and maximum sale, again ordered by customer id.
In other words, grouping allows you to combine multiple rows from the database into a single output row, based on some criteria, and select functions of those fields not involved in the grouping (minimum, maximum, total, average and so on).
group by groups data by one or more columns, and order by orders the data by one or more columns? i don't really get the question?
using group by is similar to select distinct in the aspect that only unique values for the given values will be returned. furthermore you can use aggregate functions to calculate e.g. the sum for each group.
what do you want to hear? tell me five differences between apples and oranges?
Related
I understand why the first query needs a GROUP BY, as it doesn't know which date to apply the sum to, but I don't understand why this is the case with the second query. The value that ultimately is the max amount is already contained in the table - it is not calculated like SUM is. thank you
-- First Query
select
sum(OrderSales),OrderDates
From Orders
-- Second Query
select
max(FilmOscarWins),FilmName
From tblFilm
It is not the SUM and MAX that require the GROUP BY, it is the unaggregated column.
If you just write this, you will get a single row, for the maximum value of the FilmOscarWins column across the whole table:
select
max(FilmOscarWins)
From
tblFilm
If the most Oscars any film won was 12, that one row will say 12. But there could be multiple films, all of which won 12 Oscars, so if we ask for the FilmName alongside that 12, there is no single answer.
By adding the Group By, we fundamentally change the query: instead of returning one number for the whole table, it will return one row for each group - which in this case, means one row for each film.
If you do want to get a list of all those films which had the maximum 12 Oscars, you have to do something more complicated, such as using a sub-query to first find that single number (12) and then find all the rows matching it:
select
FilmOscarWins,
FilmName
From
tblFilm
Where FilmOscarWins = (
select
max(FilmOscarWins)
From
tblFilm
)
If you want the film with the most Oscar wins, then use select top:
select top (1) f.*
From tblFilm f
order by FilmOscarWins desc;
In an aggregation query, the select columns need to be consistent with the group by columns -- the unaggregated columns in the select must match the group by.
We enter overrides based on a unique value from our tables (we have two columns with unique values for each transaction, so may or may not be primary key).
Sometimes we have to enter multiple overrides based on the same set of criteria, so it would be nice to be able to pull multiple unique values in one query that all meet the same criteria in the where clause as our system throws a warning if the same unique id is used for more than one override.
Say we have some customers that were under charged for three months and we need to enter a commission override for each of the three sales people that split the accounts for each month:
I've tried the following code, but the same value gets returned for each column:
select month, customer, product, sum(sales),
any_value(unique_id)unique_id1,
any_value(unique_id)unique_id2,
any_value(unique_id)unique_id3
from table
where customer in (j,k,l) and product = m and year = o
group by 1,2,3;
This will give me a row for each month and customer, but the values in unique_id1, unique_id2 and unique_id3 are the same on each row.
I was able to use:
select month, customer, product, sum(sales),
string_agg(unique_id, "," LIMIT 3)
from table
where customer in (j,k,l) and product = m and year = o
group by 1,2,3;
and split the unique_ids in a spreadsheet but I feel there has to be a better way to accomplish this directly in SQL.
I figure I could use a sub query and select column based on row 1,2,3, but I'm trying to eliminate the redundancy of including the same 'where' criteria in the sub query.
Beow is for BigQuery Standard SQL
I think you second query was close enough to get to something like below
#standardSQL
SELECT month, customer, product, sales,
arr[OFFSET(0)] unique_id1,
arr[SAFE_OFFSET(1)] unique_id2,
arr[SAFE_OFFSET(2)] unique_id3
FROM (
SELECT month, customer, product, SUM(sales) sales,
ARRAY_AGG(unique_id ORDER BY month DESC LIMIT 3) arr
FROM `project.dataset.table`
WHERE customer IN ('j','k','l') AND product = 'm' AND year = 2019
GROUP BY month, customer, product
)
On a report builder 3.0, i retreived some items and counted them using a Count aggregate. Now i want to order them from highest to lowest. How do i use the ORDER BY function on the aggregated column? The picture below show the a column that i want to ORDER BY it, it is ticked.
Pic
The code is vers simple as shown bellow:
SELECT DISTINCT act_id,NameOfAct,
FROM Acts
Your picture indicates you also want a Total row at the bottom:
SELECT
COALESCE(NameOfAct,'Total') NameOfAct,
COUNT(DISTINCT act_id) c
FROM Acts
GROUP BY ROLLUP(NameOfAct)
ORDER BY
CASE WHEN NameOfAct is null THEN 1 ELSE 0 END,
c DESC;
Result of example data:
NameOfAct count
-------------- -------
Act_B 3
Act_A 2
Act_Z 1
Total 6
Try it with example rows at: http://sqlfiddle.com/#!18/dbd6c/2
I looked at the Pic. So you might have duplicate acts with the same name. And you want to know the number of acts that have the same unique name.
You might want to group the results by name:
GROUP BY NameOfAct
And include the act names and their counts in the query results:
SELECT NameOfAct, COUNT(*) AS ActCount
(Since the act_id column is not included in the groups, you need to omit it in the SELECT. The DISTINCT is also not necessary anymore, since all groups are unique already.)
Finally, you can sort the data (probably descending to get the acts with the largest count on top):
ORDER BY ActCount DESC
Your complete query would become something like this:
SELECT NameOfAct, COUNT(*) AS ActCount
FROM Acts
GROUP BY NameOfAct
ORDER BY ActCount DESC
Edit:
By the way, you use field "act_id" in your SELECT clause. That's somewhat confusing. If you want to know counts, you want to look at either the complete table data or group the table data into smaller groups (with the GROUP BY clause). Then you can use aggregate functions to get more information about those groups (or the whole table), like counts, average values, minima, maxima...
Single record information, like an act's ID in your case, is typically not important if you want to use statistic/aggregate methods on grouped data. Suppose your query returns an act name which is used 10 times. Then you have 10 records in your table, each with a unique act_id, but with the same name.
If you need just one act_id that represents each group / act name (and assuming act_id is an autonumbering field), you might include the latest / largest act_id value in the query using the MAX aggregate function:
SELECT NameOfAct, COUNT(*) AS ActCount, MAX(act_id) AS LatestActId
(The rest of the query remains the same.)
My SQL table "offers" contains offers users make for products (product_ID, customer_ID, offer).
In my admin page, I want to list the products for which at least one offer exists and show the total offers existing for it.
For example,
PRODUCT #324 Total offers: 42
PRODUCT #99 Total offers: 1
etc.
My guess would be to combine a
SELECT DISTINCT product_ID FROM offers...
And in a second query, to SELECT COUNT(*) FROM offers WHERE product_ID=...
Is it the most efficient way to achieve this, or is there a way to make it inside a single query?
You can do this in one query which will get the count by grouping by the product_id:
SELECT product_ID, COUNT(*)
FROM offers
GROUP BY product_ID
As bluefeet already answered, you achieve it in single query by using group by.
(group by demo)
Another thing to mention is the order by,
select
product_id as id,
count(*) as totals
from
t
group by product_id
order by totals;
If you want to sort with the totals of hits, or if you want to sort by product_id etc.
sqlfiddle
i have a DB2 table (orderitems) that has columns named ORDERITEMS_ID and ORDERS_ID I'm looking to get a count of all of the orderitems_id that are associated with each orders_id. I can get the count but i would like the order_id associated with that count.
i've tried
SELECT COUNT(orderitems_id) as total
FROM orderitems
GROUP BY orders_id
ORDER BY total DESC
i believe this is giving me the total count of each of the items in a order_id. but i'm not sure how to add the order_id with the result set
if i try the following
SELECT orders_id, COUNT(orderitems_id) as total
FROM orderitems
GROUP BY orders_id
ORDER BY total DESC
this is a bad query
i've looked into joining but that seems to be dealing with two tables...not sure how to append this information.
Try this:
select distinct orders_id,
count(orderitems_id) as total
from orderitems
group by orders_id
order by total desc
Summarizing precisely what you want to do often helps. In this case, you want a count of orderitems_id for each distinct orders_id, e.g. for each different value of orders_id and not for each line. When you want a result depending on the different values of a column, think distinct.