I have 3 data tables.
In the entries data table I have entries with ID (entryId as primary key).
I have another table called EntryUsersRatings in there are multiple entries that have entryId field and a rating value (from 1 to 5).
(ratings are stored multiple times for one entryId).
Columns: ratingId (primary key), entryId, rating (integer value).
In the third data table I have translations of entries in the first table (with entryId, languageId and title - translation).
What I would like to do is select all entries from first data table with their titles (by language ID).
On a top of that I want average rating of each entry (which can be stored multiple times) that is stored in EntryUsersRatings.
I have tried this:
SELECT entries.entryId, EntryTranslations.title, AVG(EntryUsersRatings.rating) AS AverageRating
FROM entries
LEFT OUTER JOIN
EntryTranslations ON entries.entryId = EntryTranslations.entryId AND EntryTranslations.languageId = 1
LEFT OUTER JOIN
EntryUsersRatings ON entries.entryId = EntryUsersRatings.entryId
WHERE entries.isDraft=0
GROUP BY title, entries.entryId
isDraft is just something that means that entries are not stored with all information needed (just incomplete data - irrelevant for our case here).
Any help would be greatly appreciated.
EDIT: my solution gives me null values for rating.
Edit1: this query is working perfectly OK, I was looking into wrong database.
We also came to another solution, which gives us the same result (I hope someone will find this useful):
SELECT entries.entryId, COALESCE(x.EntryUsersRatings, 0) as averageRating
FROM entries
LEFT JOIN(
SELECT rr.entryId, AVG(rating) AS entryRating
FROM EntryUsersRatings rr
GROUP BY rr.entryId) x ON x.entryId = entries.entryId
#CyberHawk: as you are using left outer join with entries, your result will give all records from left table and matching record with your join condition from right table. but for unmatching records it will give you a null value .
check out following link for the deta:
http://msdn.microsoft.com/en-us/library/ms187518(v=sql.105).aspx
Related
I have two tables: violator_state and violator_tags
violator_state:
m_state_id
is_violating
m_translatedid
m_tag
m_violator_tag
This table holds the "tags" which has an unchanging row count of 10 in this case. The purpose is to list out each tag present, connect the full tag address (m_violator_tag) with its shorthand name (m_tag) and state whether it is in "violation". I need to use this table as reference because of the link between m_violator_tag and m_tag.
violator_tags
m_violator_id
m_eval_time_from
m_eval_time_to
m_tag
m_tag_peers
m_tag_position
This table is constantly having new rows added to it holding the information of what tags are in violation with a specific tag. So it would show T6 in violation with T1,T2,T9 ect.
I am looking to create a query which joins the two tables to show only the most recently updated (largest m_eval_time_from) for each tag.
I am using the following query to join the two tables but I expect m_translatedid and m_tag to match but they do not. Unsure why.
SELECT violator_state.m_violator_tag, violator_state.is_violating, violator_state.m_translatedid, violator_tags.m_tag, violator_tags.m_eval_time_to, violator_tags.m_tag_peers,
violator_tags.m_tag_position, violator_tags.m_eval_time_from
FROM violator_tags CROSS JOIN
violator_state
Violation_state table
violation_tags table
results of my (incorrect) query
Any suggestions on what I should try?
Your CROSS JOIN will give you a cartesian product where EVERY row in the first table is paired with ALL the rows in the second table e.g. if you have 10 rows in each, you will get 10 x 10 = 100 rows in the result! I believe you need to join the tables on the m_tag column and select the violator_tags row with the latest date. The query below should do this for you (though you haven't provided your question in a manner that makes it easy for me to double-check my code - see the link provided by a_horse_with_no_name for more on this or use a website like db-fiddle to set up your example).
SELECT vs.m_violator_tag,
vs.is_violating,
vs.m_translatedid,
vt.m_tag,
vt.m_eval_time_to,
vt.m_tag_peers,
vt.m_tag_position,
vt.m_eval_time_from
FROM violator_tags vt
JOIN violator_state vs
ON vt.m_tag = vs.m_tag
AND vt.m_eval_time_from = (SELECT MAX(vt.m_eval_time_from)
FROM violator_tags
WHERE m_tag = vt.m_tag)
I want to join three tables.
First table (contacts)contains cid (primary key),name.
Second table (familyInfo) contains fid(primary key),cid (fk),contact name and relationID (fk)
.Third table(relation type) contains relationID(primary key),relationType like father,mother,brother etc ...
Query should join all rows from first table with first matching row from second table .... Contacts which don't have any relation should display null ....only first matching relation should be shown in result
Please help,
Thank you!
I have added image of table structures and expected output for better understanding ...please click here for image
You need to use OUTER APPLY
SELECT c.cid,
c.NAME,
oa.contact_name
FROM contacts c
OUTER APPLY (SELECT TOP 1 f.contact_name
FROM familyInfo f
WHERE c.cid = f.cid
ORDER BY relationID) oa
How it works
Outer apply will return all the records from left table even thought there is no matching record found in right table
Top 1 with Order by will help you find the first matching row from second table
I have two tables: Company and Contact, with a relationship of one-to-many.
I have another table Track which identifies some of the companies as parent companies to other companies.
I want to write a SQL query that selects the parent companies from Track and the amount of contacts that each parent has.
SELECT Track.ParentId, Count(Contact.companyId)
FROM Track
INNER JOIN Contact
ON Track.ParentId = Contact.companyId
GROUP BY Track.ParentId
however The result holds less records than when I run the following query:
SELECT DISTINCT Track.ParentId
FROM Track
I tried the first query with an added DISTINCT and it returned the same results (less then what it was meant to).
You're performing an INNER JOIN with the Contact table, which means that any rows from the first table (Track in this case) with no matches to the JOINed table will not show up in your results. Try using a LEFT OUTER JOIN instead.
The COUNT with Contact.companyId will only count rows where there is a match (Contact.companyId is not NULL). Since you're counting contacts that's fine as they will count as 0. If you were trying to count some other set of data and tried to do a COUNT on a specific column (rather than COUNT(*)) then any NULL values in that column would not count towards your total, which might or might not be what you want.
I used an INNER JOIN which returns only records that are identical in both tables.
To return all records from Track table, and records that match in the Contact table, I need to use LEFT JOIN.
I have two tables. Table 1 has about 750,000 rows and table 2 has 4 million rows. Table two has an extra ID field in which I am interested, so I want to write a query that will check if the 750,000 table 1 records exist in table 2. For all those rows in table 1 that exist in table 2, I want the respective ID based on same SSN. I tried the following query:
SELECT distinct b.UID, a.*
FROM [Analysis].[dbo].[Table1] A, [Proteus_8_2].dbo.Table2 B
where a.ssn = b.ssn
Instead of getting 750,000 rows in the output, I am getting 5.4 million records. Where am i going wrong?
Please help?
You're requesting all the rows in your select if b.UID is a unique field in column two.
Also if SSN is not unique in table one you can get the higher row count than the total row count for table 2.
You need to consider what you want from table 2 again.
EDIT
You can try this to return distinct combinations of ssn and uid when ssn is found in table 2 provided that ssn and uid have a cardinality of 1:1, i.e., every unique ssn has a single unique uid.
select distinct
a.ssn,b.[UID]
from [Analysis].[dbo].[Table1] a
cross apply
( select top 1 [uid] from [Proteus_8_2].[dbo].[Table2] where ssn = a.ssn ) b
where b.[UID] is not null
Try with LEFT JOIN
SELECT distinct b.UID, a.*
FROM [Analysis].[dbo].[Table1] A LEFT JOIN [Proteus_8_2].dbo.Table2 B
on a.ssn = b.ssn
Since the order detail table is in a one-many relationship to the order table, that is the expected result of any join. If you want something different, you need to define for us the business rule that will tell us how to select only one record from the Order detail table. You cannot effectively write SQL code without understanding the business rules that of what you are trying to achieve. You should never just willy nilly select one record out of the many, you need to understand which one you want.
I have been using SQL for years, but have mostly been using the query designer within SQL Studio (etc.) to put together my queries. I've recently found some time to actually "learn" what everything is doing and have set myself the following fairly simple tasks. Before I begin, I'd like to ask the SOF community their thoughts on the questions, possible answers and any tips they may have.
The questions are;
Find all records w/ a duplicate in a particular column (e.g. a linking id is in more than 1 record throughout table)
SUM price from a linked table within the same query (select within a select?)
Explain the difference between the 4 joins; LEFT, RIGHT, OUTER, INNER
Copy data from one table to another based on SELECT and WHERE criteria
Input welcomed & appreciated.
Chris
I recommend that you start by following some tutorials on this topic. Your questions are not uncommon questions for someone moving from a beginner to intermediate level in SQL. SQLZoo is an excellent resource for learning SQL so consider following that.
In response to your questions:
1) Find all records with a duplicate in a particular column
There are two steps here: find duplicate records and select those records. To find the duplicate records you should be doing something along the lines of:
select possible_duplicate_field, count(*)
from table
group by possible_duplicate_field
having count(*) > 1
What we're doing here is selecting everything from a table, then grouping it by the field we want to check for duplicates. The count function then gives me a count of the number of items within that group. The HAVING clause indicates that we want to filter AFTER the grouping to only show the groups which have more than one entry.
This is all fine in itself but it doesn't give you the actual records that have those values on them. If you knew the duplicate values then you'd write this:
select * from table where possible_duplicate_field = 'known_duplicate_value'
We can use the SELECT within a select to get a list of the matches:
select *
from table
where possible_duplicate_field in (
select possible_duplicate_field
from table
group by possible_duplicate_field
having count(*) > 1
)
2) SUM price from a linked table within the same query
This is a simple JOIN between two tables with a SUM of the two:
select sum(tableA.X + tableB.Y)
from tableA
join tableB on tableA.keyA = tableB.keyB
What you're doing here is joining two tables together where those two tables are linked by a key field. In this case, this is a natural join which operates as you would expect (i.e. get me everything from the left table which has a matching record in the right table).
3) Explain the difference between the 4 joins; LEFT, RIGHT, OUTER, INNER
Consider two tables A and B. The concept of "LEFT" and "RIGHT" in this case are slightly clearer if you read your SQL from left to right. So, when I say:
select x from A join B ...
The left table is "A" and the right table is "B". Now, when you explicitly say "LEFT" the SQL statement you are declaring which of the two tables you are joining is the primary table. What I mean by this is: Which table do I scan through first? Incidentally, if you omit the LEFT or RIGHT, then SQL implicitly uses LEFT.
For INNER and OUTER you are declaring what to do when matches don't exist in one of the tables. INNER declares that you want everything in the primary table (as declared using LEFT or RIGHT) where there is a matching record in the secondary table. Hence, if the primary table contains keys "X", "Y" and "Z", and the secondary table contains keys "X" and "Z", then an INNER will only return "X" and "Z" records from the two tables.
When OUTER is used, we're saying: Give me everything from the primary table and anything that matches from the secondary table. Hence, in the previous example, we'd get "X", "Y" and "Z" records in the output record set. However, there would be NULLs in the fields which should have come from the secondary table for key value "Y" as it doesn't exist in the secondary table.
4) Copy data from one table to another based on SELECT and WHERE criteria
This is pretty trivial and I'm surprised you've never encountered it. It's a simple nested SELECT in an INSERT statement (this may not be supported by your database - if not, try the next option):
insert into new_table select * from old_table where x = y
This assumes the tables have the same structure. If you have different structures then you'll need to specify the columns:
insert into new_table (list, of, fields)
select list, of, fields from old_table where x = y
Let's say you have 2 tables named :
[OrderLine] with the columns [Id, OrderId, ProductId, Qty, Status]
[Product] with [Id, Name, Price]
1) all orderline of command having more than 1 line (it's technically the same as looking for duplicates on OrderId :) :
select OrderId, count(*)
from OrderLine
group by OrderId
having count(*) > 1
2) total price for all order line of the order 1000
select sum(p.Price * ol.Qty) as Price
from OrderLine ol
inner join Product p on ol.ProductId = p.Id
where ol.OrderId = 1000
3) difference between joins:
a inner join b => take all a that has a match with b. if b is not found, a will be not be returned
a left join b => take all a, match them with b, include a even if b is not found
a righ join b => b left join a
a outer join b => (a left join b) union ( a right join b)
4) copy order lines to a history table :
insert into OrderLinesHistory
(CopiedOn, OrderLineId, OrderId, ProductId, Qty)
select
getDate(), Id, OrderId, ProductId, Qty
from
OrderLine
where
status = 'Closed'
To answer #4 and to perhaps show at least some understanding of SQL and the fact this isn't HW, just me trying to learn best practise;
SET NOCOUNT ON;
DECLARE #rc int
if #what = 1
BEGIN
select id from color_mapper where product = #productid and color = #colorid;
select #rc = ##rowcount
if #rc = 0
BEGIN
exec doSavingSPROC #colorid, #productid;
END
END
END