I have a basic question regarding a problem I faced:
Let's say I have this model with these tables :
Food(Quantity, Animal_id)
Race(Race_code, Race_name)
Animal(Animal_id, Race_code)
I have been asked to find the total quantity eaten by each race with select query.
(Of course by using SUM function. Race_name is also required for the display)
But I don't know to link the attributes of these tables to go from the quantity to the race name (I only know that my reasoning will be like this Quanity->animal_id->race_code->race_name). Any help ?
Looks like a join, doesn't it? Columns that aren't aggregated (race_name in this case) have to be put into the group by clause.
select r.race_name,
sum(f.quantity) sum_quantity
from race r join animal a on a.race_code = r.race_code
join food f on f.animal_id = a.animal_id
group by r.race_name;
Using subquery:
select race_name ,(select sum(quantity) from food where animal_id in (select animal_id from animal a where r.race_code = a.race_code))
from race r
Related
I have a distinct list of part numbers from one table. It is basically a table that contains a record of all the company's part numbers. I want to add columns that will pull data from different tables but only pertaining to the part number on that row of the distinct part list.
For example: if I have part A, B, C from the unique part list I want to add columns for Purchase quantity, repair quantity, loan quantity, etc... from three totally unique tables.
So it's almost like I need 3 subqueries that will sum of that data from the different tables for each part.
Can anybody steer me in the direction of how to do this? Please and thank you so much!
One method is correlated subqueries. Something like this:
select p.*,
(select count(*)
from purchases pu
where pu.part_id = p.part_id
) as num_purchases,
(select count(*)
from repairs r
where r.part_id = p.part_id
) as num_repairs,
(select count(*)
from loans l
where l.part_id = p.part_id
) as num_loans
from parts p;
Another option is joins with aggregation before the join. Or lateral joins (which are quite similar to correlated subqueries).
I have 2 tables. One lists all the goals scored in the English Premier League and who scored it and the other, the squad numbers of each player in the league.
I want to do a join so that the table sums the total number of goals by player name, and then looks up the squad number of that player.
Table A [goal_scorer]
[]1
Table B [squads]
[]2
I have the SQL query below:
SELECT goal_scorer.*,sum(goal_scorer.number),squads.squad_number
FROM goal_scorer
Inner join squads on goal_scorer.name=squads.player
group by goal_scorer.name
The issue I have is that in the result, the sum of 'number' is too high and seems to include duplicate rows. For example, Aaron Lennon has scored 33 times, not 264 as shown below.
Maybe you want something like this?
SELECT goal_scorer.*, s.total, squads.squad_number
FROM goal_scorer
LEFT JOIN (
SELECT name, sum(number) as total
FROM goal_scorer
GROUP BY name
) s on s.name = goal_scorer.name
JOIN squads on goal_scorer.name=squads.player
There are other ways to do it, but here I'm using a sub-query to get the total by player. NB: Most modern SQL platforms support windowing functions to do this too.
Also, probably don't need the left on the sub-query (since we know there will always be at least one name), but I put it in case your actual use case is more complicated.
Can you try this if you are using sql-server?
select *
from squads
outer apply(
selecr sum(goal_scorer.number) as score
from goal_scorer where goal_scorer.name=squads.player
)x
I'm taking a database course this semester, and we're learning SQL. I understand most simple queries, but I'm having some difficulty using the count aggregate function.
I'm supposed to relate an advertisement number to a property number to a branch number so that I can tally up the amount of advertisements by branch number and compute their cost. I set up what I think are two appropriate new views, but I'm clueless as to what to write for the select statement. Am I approaching this the correct way? I have a feeling I'm over complicating this bigtime...
with ad_prop(ad_no, property_no, overseen_by) as
(select a.ad_no, a.property_no, p.overseen_by
from advertisement as a, property as p
where a.property_no = p.property_no)
with prop_branch(property_no, overseen_by, allocated_to) as
(select p.property_no, p.overseen_by, s.allocated_to
from property as p, staff as s
where p.overseen_by = s.staff_no)
select distinct pb.allocated_to as branch_no, count( ??? ) * 100 as ad_cost
from prop_branch as pb, ad_prop as ap
where ap.property_no = pb.property_no
group by branch_no;
Any insight would be greatly appreciated!
You could simplify it like this:
advertisement
- ad_no
- property_no
property
- property_no
- overseen_by
staff
- staff_no
- allocated_to
SELECT s.allocated_to AS branch, COUNT(*) as num_ads, COUNT(*)*100 as ad_cost
FROM advertisement AS a
INNER JOIN property AS p ON a.property_no = p.property_no
INNER JOIN staff AS s ON p.overseen_by = s.staff_no
GROUP BY s.allocated_to;
Update: changed above to match your schema needs
You can condense your WITH clauses into a single statement. Then, the piece I think you are missing is that columns referenced in the column definition have to be aggregated if they aren't included in the GROUP BY clause. So you GROUP BY your distinct column then apply your aggregation and math in your column definitions.
SELECT
s.allocated_to AS branch_no
,COUNT(a.ad_no) AS ad_count
,(ad_count * 100) AS ad_cost
...
GROUP BY s.allocated_to
i can tell you that you are making it way too complicated. It should be a select statement with a couple of joins. You should re-read the chapter on joins or take a look at the following link
http://www.sql-tutorial.net/SQL-JOIN.asp
A join allows you to "combine" the data from two tables based on a common key between the two tables (you can chain more tables together with more joins). Once you have this "joined" table, you can pretend that it is really one table (aliases are used to indicate where that column came from). You understand how aggregates work on a single table right?
I'd prefer not to give you the answer so that you can actually learn :)
I have the following tables:
Animals (animal_id, producer_id, ...)
Producers (prod_id, ...)
BoughtAnimals (animal_id (fk), ...)
and I'd like to make a query that tells me for each producer, how many animals it has, and how many of those animals were bought. After much thought, I tried the following approach:
select Producers.name, count (distinct A1.animal_id), count(distinct BoughtAnimals.animal_id)
from Producers, Animals A1, Animals A2, BoughtAnimals
where
Producers.nif = A1.producer_id and
Producers.nif = A2.producer_id and
BoughtAnimals.animal_id = A2.animal_id
group by Producers.name;
but I did it only by trial and error, and I find it hard to reason about several Animal tables at once. Is there any other approach to make this query? Or is this the usual way of doing it?
Try something like this
select p.name,
sum(case when ba.anyfield is not null then 1 else 0 end) bought_count,
count(1) total_count
from Producers p join Animals a on (p.nif = a.producer_id)
left join BoughtAnimals ba using (animal_id)
group by p.name;
Use a simple JOIN, you could then put the "COUNT" in a HAVING statement. See documentation for LEFT / INNER JOIN and HAVING, depending on your SGDB.
I'm ignoring the producers table for now; all the critical data you need is in the other two tables. Once this part is right, you can just do an inner join on the producers table to get the other details you need.
select a1.producer_id,
count(a1.animal_id) as num_animals,
count(b1.animal_id) as num_bought
from animals a1
left join boughtanimals b1 on (b1.animal_id = a1.animal_id)
group by producer_id;
It's not clear to me whether that last column is better named "num_bought" or "num_sold". Also not clear is what it means for a producer to "have" an animal, given that some animals are either bought or sold.
Of all the thousands of queries I've written, I can probably count on one hand the number of times I've used a non-equijoin. e.g.:
SELECT * FROM tbl1 INNER JOIN tbl2 ON tbl1.date > tbl2.date
And most of those instances were probably better solved using another method. Are there any good/clever real-world uses for non-equijoins that you've come across?
Bitmasks come to mind. In one of my jobs, we had permissions for a particular user or group on an "object" (usually corresponding to a form or class in the code) stored in the database. Rather than including a row or column for each particular permission (read, write, read others, write others, etc.), we would typically assign a bit value to each one. From there, we could then join using bitwise operators to get objects with a particular permission.
How about for checking for overlaps?
select ...
from employee_assignments ea1
, employee_assignments ea2
where ea1.emp_id = ea2.emp_id
and ea1.end_date >= ea2.start_date
and ea1.start_date <= ea1.start_date
Whole-day inetervals in date_time fields:
date_time_field >= begin_date and date_time_field < end_date_plus_1
Just found another interesting use of an unequal join on the MCTS 70-433 (SQL Server 2008 Database Development) Training Kit book. Verbatim below.
By combining derived tables with unequal joins, you can calculate a variety of cumulative aggregates. The following query returns a running aggregate of orders for each salesperson (my note - with reference to the ubiquitous AdventureWorks sample db):
select
SH3.SalesPersonID,
SH3.OrderDate,
SH3.DailyTotal,
SUM(SH4.DailyTotal) RunningTotal
from
(select SH1.SalesPersonID, SH1.OrderDate, SUM(SH1.TotalDue) DailyTotal
from Sales.SalesOrderHeader SH1
where SH1.SalesPersonID IS NOT NULL
group by SH1.SalesPersonID, SH1.OrderDate) SH3
join
(select SH1.SalesPersonID, SH1.OrderDate, SUM(SH1.TotalDue) DailyTotal
from Sales.SalesOrderHeader SH1
where SH1.SalesPersonID IS NOT NULL
group by SH1.SalesPersonID, SH1.OrderDate) SH4
on SH3.SalesPersonID = SH4.SalesPersonID AND SH3.OrderDate >= SH4.OrderDate
group by SH3.SalesPersonID, SH3.OrderDate, SH3.DailyTotal
order by SH3.SalesPersonID, SH3.OrderDate
The derived tables are used to combine all orders for salespeople who have more than one order on a single day. The join on SalesPersonID ensures that you are accumulating rows for only a single salesperson. The unequal join allows the aggregate to consider only the rows for a salesperson where the order date is earlier than the order date currently being considered within the result set.
In this particular example, the unequal join is creating a "sliding window" kind of sum on the daily total column in SH4.
Dublicates;
SELECT
*
FROM
table a, (
SELECT
id,
min(rowid)
FROM
table
GROUP BY
id
) b
WHERE
a.id = b.id
and a.rowid > b.rowid;
If you wanted to get all of the products to offer to a customer and don't want to offer them products that they already have:
SELECT
C.customer_id,
P.product_id
FROM
Customers C
INNER JOIN Products P ON
P.product_id NOT IN
(
SELECT
O.product_id
FROM
Orders O
WHERE
O.customer_id = C.customer_id
)
Most often though, when I use a non-equijoin it's because I'm doing some kind of manual fix to data. For example, the business tells me that a person in a user table should be given all access roles that they don't already have, etc.
If you want to do a dirty join of two not really related tables, you can join with a <>.
For example, you could have a Product table and a Customer table. Hypothetically, if you want to show a list of every product with every customer, you could do somthing like this:
SELECT *
FROM Product p
JOIN Customer c on p.SKU <> c.SSN
It can be useful. Be careful, though, because it can create ginormous result sets.