I am trying to create a table using complex join among multiple tables..
using LEFT OUTER JOIN will give following result
however, for all the rows where category is coming blank, i want to do an SELF JOIN on sellerid to get category filled
Related
I am trying to find the correct join construction to join together the relevant customer info from the Rentals table with the Accidents table. I often run into this issue where my joining fields aren't unique but not sure what else to join on. The accidents table only has about 1500 records but when I join it to pull in more customer data, I get like 35k records. I can do some joins but frequently have joins like this at work and I feel like a dummy because I am not sure how to troubleshoot...
SELECT a.*,
r.market,
r.date_of_birth,
r.is_blocked,
r.rate_type
FROM `accidents` a
LEFT JOIN `rentals` r -- I also tried an INNER JOIN
USING (customer_id) -- Other fields I tried to match on: Full Name
ORDER BY accident_dt DESC
I understand similar question have been posted, however my issue isn't an error rather the lack of the desired result. I'm trying to join 3 tables each with 10,000 observations and combine them in the one table, however when i use inner join the observations reduce to little over 4000. I understand that INNER JOIN is essentially an intersection but I'm expecting 10,000 observations and based on my code I don't see how that is occurring. Here is my code:
SELECT *
FROM Characteristics
INNER JOIN Prices ON Prices.pid = Characteristics.pid
INNER JOIN Locations ON Locations.tid = Characteristics.tid
;
CHARACTERISTICS
||Property_Id|| ||Beds|| ||Baths|| ||Type_ID||
PRICES
||Price|| ||Year|| ||Property_ID||
LOCATIONS
||Type_ID|| ||X coord|| ||Y coord||
Those are representative of the tables I didn't include numbers because of formatting issues but as you can imagine the number contained in Property_id and Type_id are the same for all columns regardless of table, what i would like is one table with each of the respective columns containing 10,000 rows, i've checked for NA values on R and they're all of the same length.
If you want to keep all characteristics -- even when there are no matches in the other tables -- then use left join:
SELECT *
FROM Characteristics c LEFT JOIN
Prices p
ON p.pid = c.pid LEFT JOIN
Locations l
ON l.tid = c.tid;
I am trying to get two tables that aren't related to pull a column of data each.
I have one table called AlphaData and one called TLAuth. Each includes a column that is labelled invoice and I need to pull both columns so I can at least start a comparison. TLAuth will include some of the invoice numbers from AlphaData, but not all of them.
Right now I am using the following code:
SELECT Alphadata.Invoice, TLAuth.Invoice
FROM Alphadata
INNER JOIN TlAuth
ON TLauth.TLAUthID = Alphadata.TLAUthID;
But every time I run this it comes up totally blank. There is definitely data in there, I can pull one column of data from each, but not both at the same time. I have even setup a relationship (1 to Many from TL Auth to Alphadata) and it doesn't seem to work so any help would be grand.
If the tables could not match you should use left join
SELECT Alphadata.Invoice, TLAuth.Invoice
From Alphadata
LEFT JOIN TlAuth ON TLauth.TLAUthID=Alphadata.TLAUthID;
I'm having a little confusion with a certain example.
I am supposed to list all orders and their corresponding details.
This is what I'm doing:
SELECT *
FROM Orders
LEFT OUTER JOIN [Order Details]
ON Orders.OrderID=[Order Details].OrderID;
This gives the number of rows = 2155.
Now the problem is, the number of rows in Orders Table is 830...how can left outer join create more rows ?
By definition of left outer join, all the rows from the left table are taken and matching records from the second table are added.
I checked the number of rows in the Order Details table..that is 2155.
Why is left outer join using all rows from Order Details table?
LEFT JOIN takes all the details from the table you define on the left side of the join and match records from the right table.
If there's no match, all columns of the right table have NULL values.
If there's a match, all matching records from the right table are returned. If your relationship is 1-to-many (as in your case), it means that there may be more than one record returned from the right table for each record in the left table.
LEFT OUTER JOIN will match all records in the right table, just as an INNER JOIN will. The difference is a LEFT JOIN will preserve records from the left table with no match in the right table.
In this scenario, all records in [ORDER DETAILS] have a corresponding entry in ORDERS, which is why the total number of records matches the number of rows in ORDER DETAILS
Based on the table descriptions, this is exactly what you want. Having an ORDER DETAIL without an ORDER would be a much more serious issue.
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