Given scenario:
table fd
(cust_id, fd_id) primary-key and amount
table loan
(cust_id, l_id) primary-key and amount
I want to list all customers who have a fixed deposit with an amount less than the sum of all their loans.
Query:
SELECT cust_id
FROM fd
WHERE amount
<
(SELECT sum(amount)
FROM loan
WHERE fd.cust_id = loan.cust_id);
OR should we use
SELECT cust_id
FROM fd
WHERE amount
<
(SELECT sum(amount)
FROM loan
WHERE fd.cust_id = loan.cust_id group by cust_id);
A customer can have multiple loans but one FD is considered at a time.
GROUP BY can be omitted in this case, because there is only (one) aggregate function(s) in the SELECT list and all rows are guaranteed to belong to the same group of cust_id ( by the WHERE clause).
The aggregation will be over all rows with matching cust_id in both cases. So both queries are correct.
This would be a cleaner another way to implement the same thing:
SELECT fd.cust_id
FROM fd
JOIN loan USING (cust_id)
GROUP BY fd.cust_id, fd.amount
HAVING fd.amount < sum(loan.amount)
There is one difference: rows with identical (cust_id, amount) in fd only appear once in the result of my query, while they would appear multiple times in the original.
Either way, if there is no matching row with a non-null amount in table loan, you get no rows at all. I assume you are aware of that.
There are no need for GROUP BY since you filtered data by cust_id. In any case inner query will return the same result.
No, it isn't, because you calculate sum(amount) for customer with id = fd.cust_id, so for a single customer.
However, if somehow your subquery calculate sum for more than one customer, the group by would cause the subquery to generate more than one row and this will cause the condition(<) to fail, and thus, the query to fail.
A query with an aggregate like sum but without a group by will output one group. The aggregates will be computed over all matching rows.
A subquery in a condition clause is only allowed to return one row. If the subquery returned multiple rows, what would the following expression mean?
where 1 > (... subquery ...)
So the group by must be omitted; you would even get an error for your second query.
N.B. When you specify all, any, or some a subquery can return multiple rows:
where 1 > ALL (... subquery ...)
But it's easy to see why that doesn't make sense in your case; you'd compare one customer's data to that of another.
Related
Q1: After using the Group By function, why does it only output one row of each group at most? Does this mean that having is supposed to filter the group rather than filter the records in each group?
Q2: I want to find the records in each group whose ages are greater than the average age of that group. I tried the following, but it returns nothing. How should I fix this?
SELECT *, avg(age) FROM Mytable Group By country Having age > avg(age)
Thanks!!!!
You can calculate the average age for each country in a subquery and join that to your table for filtering:
SELECT mt.*, MtAvg.AvgAge
FROM Mytable mt
inner join
(
select mtavgs.country
, avg(mtavgs.age) as AvgAge
from Mytable mtavgs
group by mtavgs.country
) MTAvg
on mtavg.country=mt.country
and mt.Age > mtavg.AvgAge
GROUP BY returns always 1 row per unique combination of values in the GROUP BY columns listed (provided that they are not removed by a HAVING clause). The subquery in our example (alias: MTAvg) will calculate a single row per country. We will use its results for filtering the main table rows by applying the condition in the INNER JOIN clause; we will also report that average by including the calculated average age.
GROUP BY is a keyword that is called an aggregate function. Check this out here for further reading SQL Group By tutorial
What it does is it lumps all the results together into one row. In your example it would lump all the results with the same country together.
Not quite sure what exactly your query needs to be to solve your exact problem. I would however look into what are called window functions in SQL. I believe what you first need to do is write a window function to find the average age in each group. Then you can write a query to return the results you need
Depending on your dbms type and version, you may be able to use a "window function" that will calculate the average per country and with this approach it makes the calculation available on every row. Once that data is present as a "derived table" you can simply use a where clause to filter for the ages that are greater then the calculated average per country.
SELECT mt.*
FROM (
SELECT *
, avg(age) OVER(PARTITION BY country) AS AvgAge
FROM Mytable
) mt
WHERE mt.Age > mt.AvgAge
I'm having trouble understanding this error through all the researching I have done. I have the following query
SELECT M.[PO Concatenate], Sum(M.SumofAward) AS TotalAward, (SELECT TOP 1 M1.[Material Group] FROM
[MGETCpreMG] AS M1 WHERE M1.[PO Concatenate]=M.[PO Concatenate] ORDER BY M1.SumofAward DESC) AS TopGroup
FROM MGETCpreMG AS M
GROUP BY M.[PO Concatenate];
For a brief instance it reviews the results I want, but then the "At most one record can be returned by this subquery" error comes and wipes all the data to #Name?
For context, [MGETCpreMG] is a query off a main table [MG ETC] that was used to consolidate Award for differing Material Groups on a PO transaction ([PO Concatenate])
SELECT [MG ETC].[PO Concatenate], Sum([MG ETC].Award) AS SumOfAward, [MG ETC].[Material Group]
FROM [MG ETC]
GROUP BY [MG ETC].[PO Concatenate], [MG ETC].[Material Group]
ORDER BY [MG ETC].[PO Concatenate];
I'm thinking it lies in my inability to understand how to utilize a subquery.
In the case in which the query can return more then one value? Simply add an additonal sort by.
So, a common sub query might be to get the last invoice. So you might have:
select ID, CompanyName,
(SELECT TOP 1 InvoiceDate from tblInvoice
where tblInvoice.CustomerID = tblCompany.ID
Order by InvoiceDate DESC)
As LastInvoiceDate
From tblCustomers
Now the above might work for some time, but then it will blow up since you might have two invoices for the same day!
So, all you have to do is add that extra order by clause - say on the PK of the child table like this:
Order by InvoiceDate DESC,ID DESC)
So top 1 will respect the "additional" order columns you add, and thus only ever return one row - even if there are multiple values that match the top 1 column.
I suppose in the above we could perhaps forget the invoiceDate and always take the top most last autonumber ID, but for a lot of queries, you can't always be sure - it might be we want the last most expensive invoice amount. And again, if the max value (top) was the same for two large invoice amounts, then again two rows could be return. So, simply add the extra ORDER BY clause with an 2nd column that further orders the data. And thus top 1 will only pull the first value. Your example of a top group is such an example. Just tack on the extra order by "ID" or whatever the auto number ID column is.
I have a table of existing customers and another table of potential customers. I want to return a list of potential customers rank ordered by the number of radii of existing purchasers that they appear in.
There are many rows in the potential customers table per each existing customer, and the radius around a given existing customer could encompass multiple potential customers. I want to return a list of potential customers ordered by the count of the existing customer radii that they fall within.
SELECT pur.contact_id AS purchaser, count(pot.*) AS nearby_potential_customers
FROM purchasers_geocoded pur, potential_customers_geocoded pot
WHERE ST_DWithin(pur.geom,pot.geom,1000)
GROUP BY purchaser;
Does anyone have advice on how to proceed?
EDIT:
With some help, I wrote this query, which seems to do the job, but I'm verifying now.
WITH prequalified_leads_table AS (
SELECT *
FROM nearby_potential_customers
WHERE market_val > 80000
AND market_val < 120000
)
, proximate_to_existing AS (
SELECT pot.prop_id AS prequalified_leads
FROM purchasers_geocoded pur, prequalified_leads_table pot
WHERE ST_DWithin(pot.geom,pur.geom,100)
)
SELECT prequalified_leads, count(prequalified_leads)
FROM proximate_to_existing
GROUP BY prequalified_leads
ORDER BY count(*) DESC;
I want to return a list of potential customers ordered by the count of the existing customer radii that they fall within.
Your query tried the opposite of your statement, counting potential customers around existing ones.
Inverting that, and after adding some tweaks:
SELECT pot.contact_id AS potential_customer
, rank() OVER (ORDER BY pur.nearby_customers DESC
, pot.contact_id) AS rnk
, pur.nearby_customers
FROM potential_customers_geocoded pot
LEFT JOIN LATERAL (
SELECT count(*) AS nearby_customers
FROM purchasers_geocoded pur
WHERE ST_DWithin(pur.geom, pot.geom, 1000)
) pur ON true
ORDER BY 2;
I suggest a subquery with LEFT JOIN LATERAL ... ON true to get counts. Should make use of the spatial index that you undoubtedly have:
CREATE INDEX ON purchasers_geocoded USING gist (geom);
Thereby retaining rows with 0 nearby customers in the result - your original join style would exclude those. Related:
What is the difference between LATERAL and a subquery in PostgreSQL?
Then ORDER BY the resulting nearby_customers in the outer query (not: nearby_potential_customers).
It's not clear whether you want to add an actual rank. Use the window function rank() if so. I made the rank deterministic while being at it, breaking ties with an additional ORDER BY expression: pot.contact_id. Else, peers are returned in arbitrary order which can change for every execution.
ORDER BY 2 is short syntax for "order by the 2nd out column". See:
Select first row in each GROUP BY group?
Related:
How do I query all rows within a 5-mile radius of my coordinates?
Currently have a single table with large amount of data in access, due to the size I couldn't easily work with it in Excel any more.
I'm partially there on a query to pull data from this table.
7 Column table
One column GL_GL_NUM contains a transaction number. ~ 75% of these numbers are pairs. I'm trying to pull the records (all columns information) for each unique transaction number in this column.
I have put together some code from googling that hypothetically should work but I think I'm missing something on the syntax or simply asking access to do what it cannot.
See below:
SELECT SOURCE_FUND, GLType, Contract, Status, Debit, Credit, GL_GL_NUM
FROM Suspense
JOIN (
SELECT TC_TXN_NUM TXN_NUM, COUNT(GL_GL_NUM) GL_NUM
FROM Suspense
GROUP BY TC_TXN_NUM HAVING COUNT(GL_GL_NUM) > 1 ) SUB ON GL_GL_NUM = GL_NUM
Hey Beth is this the suggested code? It says there is a syntax error in the FROM clause. Thanks.
SELECT * from SuspenseGL
JOIN (
SELECT TC_TXN_NUM, COUNT(GL_GL_NUM) GL_NUM
FROM Suspense
GROUP BY TC_TXN_NUM
HAVING COUNT(GL_GL_NUM) > 1
Do you want detailed results (all rows and columns) or aggregate results, with one row per tx number?
If you want an aggregate result, like the count of distinct transaction numbers, then you need to apply one or more aggregate functions to any other columns you include.
If you run
SELECT TC_TXN_NUM, COUNT(GL_GL_NUM) GL_NUM
FROM Suspense
GROUP BY TC_TXN_NUM
HAVING COUNT(GL_GL_NUM) > 1
you'll get one row for each distinct txn, but if you then join those results back with your original table, you'll have the same number of rows as if you didn't join them with distinct txns at all.
Is there a column you don't want included in your results? If not, then the only query you need to work with is
select * from suspense
Considering your column names, what you may want is:
SELECT SOURCE_FUND, GLType, Contract, Status, sum(Debit) as sum_debit,
sum(Credit) as sum_credit, count(*) as txCount
FROM Suspense
group by
SOURCE_FUND, GLType, Contract, Status
based on your comments, if you can't work with aggregate results, you need to work with them all:
Select * from suspense
What's not working? It doesn't matter if 75% of the txns are duplicates, you need to send out every column in every row.
OK, let's say
Select * from suspense
returns 8 rows, and
select GL_GL_NUM from suspense group by GL_GL_NUM
returns 5 rows, because 3 of them have duplicate GL_GL_NUMs and 2 of them don't.
How many rows do you want in your result set? if you want less than 8 rows back, you need to perform some sort of aggregate function on each column you want returned.
You could do something like the following:
SELECT S.* FROM
SUSPENSE AS S
INNER JOIN (SELECT DISTINCT GL_GL_NUM, MIN(ID) AS ID FROM SUSPENSE
GROUP BY GL_GL_NUM) AS S2
ON S.ID = S2.ID
AND S.GL_GL_NUM = S2.GL_GL_NUM
Which would return a single row for a unique gl_gl_num. However if the other rows have different data it will not be shown. You would have to either aggregate that data up using SUM(Credit), SUM(Debit) and then GROUP BY the gl_gl_num.
I have attached a SQL Fiddle to demonstrate my results and make this clearer.
http://sqlfiddle.com/#!3/8284f/2
I have a table that stores transaction information. Each transaction is has a unique (auto incremented) id column, a column with the customer's id number, a column called bill_paid which indicates if the transaction has been paid for by the customer with a yes or no, and a few other columns which hold other information not relevant to my question.
I want to select all customer ids from the transaction table for which the bill has not been paid, but if the customer has had multiple transactions where the bill has not been paid I DO NOT want to select them more than once. This way I can generate that customer one bill with all the transactions they owe for instead of a separate bill for each transaction. How would I build a query that did that for me?
Returns exactly one customer_id for each customer with bill_paid equal to 'no':
SELECT
t.customer_id
FROM
transactions t
WHERE
t.bill_paid = 'no'
GROUP BY
t.customer_id
Edit:
GROUP BY summarises your resultset.
Caveat: Every column selected must be either 'grouped by' or aggregated in some fashion. As shown by nikic you could use SUM to get the total amount owed, e.g.:
SELECT
t.customer_id
, SUM(t.amount) AS TOTAL_OWED
FROM
transactions AS t
WHERE
t.bill_paid = 'no'
GROUP BY
t.customer_id
t is simply an alias.
So instead of typing transactions everywhere you can now simply type t. The alias is not necessary here since you query only one table, but I find them invaluable for larger queries. You can optionally type AS to make it more clear that you're using an alias.
You might try the Group By operator, eg group by the customer.
SELECT customer, SUM(toPay) FROM .. GROUP BY customer