I just started using SQL and I need some help. I have 4 tables in a database. All four are connected with each other. I need to find the amount of unique transactions but can't seem to find it.
Transactions
transaction_id pk
name
Partyinvolved
transaction.id pk
partyinvolved.id
type (buyer, seller)
PartyCompany
partyinvolved.id
Partycompany.id
Companies
PartyCompany.id pk
sector
pk = primary key
The transaction is unique if the conditions are met.
I only need a certain sector out of Companies, this is condition1. Condition2 is a condition inside table Partyinvolved but we first need to execute condition1. I know the conditions but do not know where to put them.
SELECT *
FROM group
INNER JOIN groupB ON groupB.group_id = group.id
INNER JOIN companies ON companies.id = groupB.company_id
WHERE condition1 AND condition2 ;
I want to output the amount of unique transactions with the name.
It is a bit unclear what you are asking as your table definitions look like your hinting at column meanings more than names such as partycompany.id you are probably meaning the column that stores the relationship to PartyCompany column Id......
Anyway, If I follow that logic and I look at your questions about wanting to know where to limit the recordsets during the join. You could do it in Where clause because you are using an Inner Join and it wont mess you your results, but the same would not be true if you were to use an outer join. Plus for optimization it is typically best to add the limiter to the ON condition of the join.
I am also a bit lost as to what exactly you want e.g. a count of transactions or the actual transactions associated with a particular sector for instance. Anyway, either should be able to be derived from a basic query structure like:
SELECT
t.*
FROM
Companies co
INNER JOIN PartyCompancy pco
ON co.PartyCompanyId = pco.PartyCompanyId
INNER JOIN PartyInvolved pinv
ON pco.PartyInvolvedId = pinv.PartyInvolvedId
AND pinv.[type] = 'buyer'
INNER JOIN Transactions t
ON ping.TransactionId = t.TransactionId
WHERE
co.sector = 'some sector'
Related
I have a query with joins that is not using the index that would be the best match and I am looking for help to correct this.
I have the following query:
select
equipment.name,purchaselines.description,contacts.name,vendors.accountNumber
from purchaselines
left join vendors on vendors.id = purchaselines.vendorId
left join contacts on contacts.id = vendors.contactId
left join equipment on equipment.id = purchaselines.equipmentId
where contacts.id = 12345
The table purchaselines has an index on the column vendorId, which is the proper index to use. When the query is run, I know the value of contacts.id which is joined to vendors.contactId which is joined to purchaselines.vendorId.
What is the proper way to run this query? Currently, no index is used on the table purchaselines.
If you are intending to query a specific contact, I would put THAT first since that is the primary basis. Additionally, you had left-joins to the other tables (vendors, contacts, equipment). So by having a WHERE clause to the CONTACTS table forces the equation to become an INNER JOIN, thus REQUIRING.
That said, I would try to rewrite the query as (also using aliases for simplified readability of longer table names)
select
equipment.name,
purchaselines.description,
contacts.name,
vendors.accountNumber
from
contacts c
join vendors v
on c.id = v.contactid
join purchaselines pl
on v.id = pl.vendorid
join equipment e
on pl.equipmentid = e.id
where
c.id = 12345
Also notice the indentation of the JOINs helps readability (IMO) to see how/where each table gets to the next in a more hierarchical manner. They are all regular inner JOIN context.
So, the customer ID will be the first / fastest, then to vendors by that contact ID which should optimize the join to that. Then, I would expect the purchase lines to have an index on vendorid optimizing that. And finally, the equipment table on ITs PK.
FEEDBACK Basic JOIN clarification.
JOIN is just the explicit statement of how two tables are related. By listing them left-side and right-side and the join condition showing on what relationship is between them is all.
Now, in your data example, each table is subsequently nested under the one prior. It is quite common though that one table may link to multiple other tables. For example an employee. A customer could have an ethnicity ID linking to an ethnicity lookup table, but also, a job position id also linking to a job position lookup table. That might look something like
select
e.name,
eth.ethnicity,
jp.jobPosition
from
employee e
join ethnicitiy eth
on e.ethnicityid = eth.id
join jobPosition jp
on e.jobPositionID = jp.id
Notice here that both ethnicity and jobPosition are at the same hierarchical level to the employee table scenario. If, for example, you wanted to further apply conditions that you only wanted certain types of employees, you can just add your logical additional conditions directly at the location of the join such as
join jobPosition jp
on e.jobPositionID = jp.id
AND jp.jobPosition = 'Manager'
This would get you a list of only those employees who are managers. You do not need to explictily add a WHERE condition if you already include it directly at the JOIN/ON criteria. This helps keeping the table-specific criteria at the join if you ever find yourself needing LEFT JOINs.
I have an UltraGrid displaying customer information in it. The way the database is set up, there are 2 tables. Customers and Customer_Addresses. I need to be able to display all of the columns from Customers as well as Town and Region from Customer_Addresses, but I'm under the impression that I'd need Town and Region columns in the Customer table to be able to do this? I've never used an INNER JOIN before so I'm not sure if this is true or not, so can anybody give me pointers on how to do this, or if I need the matching columns or not?
Does it even require an INNER JOIN, or is there an alternative way to do this?
Below are the design views of both of the tables - Is it possible to display Add4 and Add5 from Customer_Addresses with all of Customers?
As long as you have another key column you can use to link the tables (ex. ID_Column), it is better that you use LEFT JOIN.
Example:
SELECT c.col1, ... , c.colN, a.town, a.region FROM Customers c
LEFT JOIN Customer_Addresses a ON a.ID_Column = c.ID_Column
In order to clarify how JOIN types work, look at this picture:
In our case, using a LEFT JOIN will take all information from the Customers table, along with any found matching (on ID) information from Customer_Addresses table.
First of all you need some column in common in two tables, all what you have to do is:
CREATE TABLE all_things
AS
SELECT * (or columns that you want to have in the new table)
FROM Costumers AS a1
INNER JOIN Customer_Addresses AS a2 ON a1.column_in_common = a2.column_in_common
The point is what kind of join do you want.
If you can continue the process without having information in table Costumers or in table Customer_Addresses maybe you need OUTER JOIN or other kind of JOIN.
I have following query, but it doesn't return any results for where clauses, even when there is row with that kind of name what is queried. If I remove where clause, then all records in Company table which have OfficeLocation table are returned. What is wrong in my query?
SELECT c.*
FROM [MyDb].[dbo].[Company] AS c
INNER JOIN [MyDb].[dbo].[CompanyOfficeLocation] AS col ON c.Id = col.CompanyId
INNER JOIN [MyDb].[dbo].[OfficeLocation] AS ol ON ol.Id = col.OfficeLocationId
WHERE ol.Name like '%Actual Name In This Table%';
Table structure :
Company
Id
etc ...
CompanyOfficeLocation
CompanyId
OfficeLocationId
OfficeLocation
Id
etc ...
Two things for a record to show up given your query:
The OfficeLocation you specified (given the ol.Name value) must have an Id value that is used by a record in the CompanyOfficeLocation table in its OfficeLocationId.
The CompanyOfficeLocation record that you got in #1 must have a CompanyId that exists in the Company table.
If any of those two criteria are not met, then no records will show up in your query result. The INNER JOIN is essentially an 'AND' clause. If a record could not be related to at least one INNER JOINed table, then that record will not show up at all.
If you want a record to show up despite not having any related records in the joined tables, you may want to consider using OUTER JOINs. A RIGHT JOIN in your case to be exact.
I do not find any mistake however I'd suggest you switch the columns after ON when joining to maintain standards.
Instead of - INNER JOIN [MyDb].[dbo].[OfficeLocation] AS ol ON ol.Id = col.OfficeLocationId
Do - INNER JOIN [MyDb].[dbo].[OfficeLocation] AS ol ON col.OfficeLocationId = ol.Id
I have a database with two tables
One with games
and one with participants
A game is able to have more participants and these are in a different table.
Is there a way to combine these two into one query?
Thanks
You can combine them using the JOIN operator.
Something like
SELECT *
FROM games g
INNER JOIN participants p ON p.gameid = g.gameid
Explanation on JOIN operators
INNER JOIN - Match rows between the two tables specified in the INNER
JOIN statement based on one or more
columns having matching data.
Preferably the join is based on
referential integrity enforcing the
relationship between the tables to
ensure data integrity.
o Just to add a little commentary to the basic definitions
above, in general the INNER JOIN
option is considered to be the most
common join needed in applications
and/or queries. Although that is the
case in some environments, it is
really dependent on the database
design, referential integrity and data
needed for the application. As such,
please take the time to understand the
data being requested then select the
proper join option.
o Although most join logic is based on matching values between
the two columns specified, it is
possible to also include logic using
greater than, less than, not equals,
etc.
LEFT OUTER JOIN - Based on the two tables specified in the join
clause, all data is returned from the
left table. On the right table, the
matching data is returned in addition
to NULL values where a record exists
in the left table, but not in the
right table.
o Another item to keep in mind is that the LEFT and RIGHT OUTER
JOIN logic is opposite of one another.
So you can change either the order of
the tables in the specific join
statement or change the JOIN from left
to right or vice versa and get the
same results.
RIGHT OUTER JOIN - Based on the two tables specified in the join
clause, all data is returned from the
right table. On the left table, the
matching data is returned in addition
to NULL values where a record exists
in the right table but not in the left
table.
Self -Join - In this circumstance, the same table is
specified twice with two different
aliases in order to match the data
within the same table.
CROSS JOIN - Based on the two tables specified in the join clause, a
Cartesian product is created if a
WHERE clause does filter the rows.
The size of the Cartesian product is
based on multiplying the number of
rows from the left table by the number
of rows in the right table. Please
heed caution when using a CROSS JOIN.
FULL JOIN - Based on the two tables specified in the join clause,
all data is returned from both tables
regardless of matching data.
example
table Game has columns (gameName, gameID)
table Participant has columns (participantID, participantName, gameID)
the GameID column is the "link" between the 2 tables. you need a common column you can join between 2 tables.
SELECT gameName, participantName
FROM Game g
JOIN Participat p ON g.gameID = p.gameID
This will return a data set of all games and the participants for those games.
The list of games will be redundant unless you structure it some other way due to multiple participants to that game.
sample data
WOW Bob
WOW Jake
StarCraft2 Neal
Warcraft3 James
Warcraft3 Rich
Diablo Chris
I have a table B with cids and cities. I also have a table C that has these cids with extra information. I want to list all the cids in table C that are associated with ALL appearances of a given city in Table B.
My current solution relies on counting the number of times the given city appears in Table B and selecting only the cids that appear that many times. I don't know all the SQL syntax yet, but is there a way to select for this kind of pattern?
My current solution:
SELECT Agents.aid
FROM Agents, Customers, Orders
WHERE (Customers.city='Duluth')
AND (Agents.aid = Orders.aid)
AND (Customers.cid = Orders.cid)
GROUP BY Agents.aid
HAVING count(Agents.aid) > 1
It only works because I know right now with the HAVING statement.
Thanks for the help. I wasn't sure how to google this problem, since it's pretty specific.
EDIT: I'm pinpointing my problem a bit. I need to know how to determine if EVERY row in a table has a certain value for a field. Declaring a variable and counting the rows in a sub-selection and filtering out my results by IDs that appear that many times works, but It's really ugly.
There HAS to be a way to do this without explicitly count()ing rows. I hope.
Not an answer to your question, but a general improvement.
I'd recommend using JOIN syntax to join your tables together.
This would change your query to be:
SELECT Agents.aid
FROM Agents
INNER JOIN Orders
ON Agents.aid = Orders.aid
INNER JOIN Customers
ON Customers.cid = Orders.cid
WHERE Customers.city='Duluth'
GROUP BY Agents.aid
HAVING count(Agents.aid) > 1
What variant of SQL are you using?
To start with, you can (and should) use JOIN instead of doing it in the WHERE clause, e.g.,
select Agents.aid
from Agents
join Orders on Agents.aid = Orders.aid
join Customers on Customers.cid = Orders.cid
where Customers.city = 'Duluth'
group by Agents.aid
having count(Agents.aid) > 1
After that, I'm afraid I might be a little lost. Using the table names in your example query, what (in English, not pseudocode) are you trying to retrieve? For example, I think your sample query is retrieving the PK for all Agents that have been involved in at least 2 Orders involving Customers in Duluth.
Also, some table definitions for Agents, Orders, and Customers might help (then again, they might be irrelevant).
I'm not sure if I understood you problem, but I think the following query is what you want:
SELECT *
FROM customers b
INNER JOIN orders c USING (cid)
WHERE b.city = 'Duluth'
AND NOT EXISTS (SELECT 1
FROM customers b2
WHERE b2.city = b.city
AND b2.cid <> cid);
Probably you will need some indexes on these columns.