I don't even know if I am doing this query the right way.
There is a Sandwiches table that has some 7 fields and 2 of them are comboboxes (Type and Bread).
So I made a query that combines all of the comboboxes values into one query, like this:
SELECT TypesAndBreads.TBName, TypesAndBreads.Type
FROM (SELECT [Sandwiches Types].[Sandwich Type] As TBName, "Sandwich Type" As Type
FROM [Sandwiches Types]
UNION ALL
SELECT Breads.Bread As TBName, "Bread" As Type
FROM Breads) AS TypesAndBreads;
I get the flat values of the tables now I want to count all the sandwiches under each TypesAndBreads.TBName. I have this, just to make sure it works with all the Sandwiches:
SELECT TypesAndBread.Type, TypesAndBread.TBName,
(SELECT Count(Sandwiches.[SandwichID]) As SandwichCount
FROM Sandwiches) As SandwichCount
FROM TypesAndBread;
But I want to reference the current Type and TBName inside the subquery. Something like this:
SELECT TypesAndBread.Type, TypesAndBread.TBName,
(SELECT Count(Sandwiches.[SandwichID]) As SandwichCount
FROM Sandwiches
WHERE Sandwiches.[TypesAndBread.Type] = Sandwiches.[TypesAndBread.TBName]) As SandwichCount
FROM TypesAndBread;
But of course this doesn't work. I didn't think it will, just thought of giving it a try. I was thinking of maybe constructing the query with VBA when they open the Report that this query is going to be based of.
So I guess my question is: Is there a way to reference the current selected fields in a subquery? Or is there a different way to approach this?
Thanks for the help
EDIT:
My table structure is like this:
Sandwiches's fields
| SandwichID | Name | Date Added | Chef | Sandwich Type | Bread | Reviewed By |
where Sandwich Type and Bread are Lookup fields for these tables:
Sandwiches Types's fields
| Sandwich Type |
Breads's fields
| Bread |
The TypesAndBreads query combined the Sandwiches Types and Breads tables, but the reason for that is so that I can get the count of all the sandwiches that have that Type or bread. A result like this:
+=============================================+
| Type | TBName | SandwichCount |
+=============================================+
| Sandwich Type | Turkey Club | 10 |
| Bread | Italian | 5 |
| Bread | Garlic | 8 |
+---------------------------------------------+
the example result's first row basicly says there are 10 sandwiches in record with the Sandwich Type field equal to Turkey Club.
I hope that explains it better.
Not sure if Access supports it, but in most engines (including SQL Server) this is called a correlated subquery and works fine:
SELECT TypesAndBread.Type, TypesAndBread.TBName,
(
SELECT Count(Sandwiches.[SandwichID]) As SandwichCount
FROM Sandwiches
WHERE (Type = 'Sandwich Type' AND Sandwiches.Type = TypesAndBread.TBName)
OR (Type = 'Bread' AND Sandwiches.Bread = TypesAndBread.TBName)
) As SandwichCount
FROM TypesAndBread
This can be made more efficient by indexing Type and Bread and distributing the subqueries over the UNION:
SELECT [Sandwiches Types].[Sandwich Type] As TBName, "Sandwich Type" As Type,
(
SELECT COUNT(*) As SandwichCount
FROM Sandwiches
WHERE Sandwiches.Type = [Sandwiches Types].[Sandwich Type]
)
FROM [Sandwiches Types]
UNION ALL
SELECT [Breads].[Bread] As TBName, "Bread" As Type,
(
SELECT COUNT(*) As SandwichCount
FROM Sandwiches
WHERE Sandwiches.Bread = [Breads].[Bread]
)
FROM [Breads]
I was over-complicating myself. After taking a long break and coming back, the desired output could be accomplished by this simple query:
SELECT Sandwiches.[Sandwich Type], Sandwich.Bread, Count(Sandwiches.[SandwichID]) AS [Total Sandwiches]
FROM Sandwiches
GROUP BY Sandwiches.[Sandwiches Type], Sandwiches.Bread;
Thanks for answering, it helped my train of thought.
Related
I take a Database course in which we have listings of AirBnBs and need to be able to do some SQL queries in the Relationship-Model we made from the data, but I struggle with one in particular :
I have two tables that we are interested in, Billing and Amenities. The first one have the id and price of listings, the second have id and wifi (let's say, to simplify, that it equals 1 if there is Wifi, 0 otherwise). Both have other attributes that we don't really care about here.
So the query is, "What is the difference in the average price of listings with and without Wifi ?"
My idea was to build to JOIN-tables, one with listings that have wifi, the other without, and compare them easily :
SELECT avg(B.price - A.price) as averagePrice
FROM (
SELECT Billing.price, Billing.id
FROM Billing
INNER JOIN Amenities
ON Billing.id = Amenities.id
WHERE Amenities.wifi = 0
) A, (
SELECT Billing.price, Billing.id
FROM Billing
INNER JOIN Amenities
ON Billing.id = Amenities.id
WHERE Amenities.wifi = 1) B
WHERE A.id = B.id;
Obviously this doesn't work... I am pretty sure that there is a far easier solution to it tho, what do I miss ?
(And by the way, is there a way to compute the absolute between the difference of price ?)
I hope that I was clear enough, thank you for your time !
Edit : As mentionned in the comments, forgot to say that, but both tables have idas their primary key, so that there is one row per listing.
Just use conditional aggregation:
SELECT AVG(CASE WHEN a.wifi = 0 THEN b.price END) as avg_no_wifi,
AVG(CASE WHEN a.wifi = 1 THEN b.price END) as avg_wifi
FROM Billing b JOIN
Amenities a
ON b.id = a.id
WHERE a.wifi IN (0, 1);
You can use a - if you want the difference instead of the specific values.
Let's assume we're working with data like the following (problems with your data model are noted below):
Billing
+------------+---------+
| listing_id | price |
+------------+---------+
| 1 | 1500.00 |
| 2 | 1700.00 |
| 3 | 1800.00 |
| 4 | 1900.00 |
+------------+---------+
Amenities
+------------+------+
| listing_id | wifi |
+------------+------+
| 1 | 1 |
| 2 | 1 |
| 3 | 0 |
+------------+------+
Notice that I changed "id" to "listing_id" to make it clear what it was (using "id" as an attribute name is problematic anyways). Also, note that one listing doesn't have an entry in the Amenities table. Depending on your data, that may or may not be a concern (again, refer to the bottom for a discussion of your data model).
Based on this data, your averages should be as follows:
Listings with wifi average $1600 (Listings 1 and 2)
Listings without wifi (just 3) average 1800).
So the difference would be $200.
To achieve this result in SQL, it may be helpful to first get the average cost per amenity (whether wifi is offered). This would be obtained with the following query:
SELECT
Amenities.wifi AS has_wifi,
AVG(Billing.price) AS avg_cost
FROM Billing
INNER JOIN Amenities ON
Amenities.listing_id = Billing.listing_id
GROUP BY Amenities.wifi
which gives you the following results:
+----------+-----------------------+
| has_wifi | avg_cost |
+----------+-----------------------+
| 0 | 1800.0000000000000000 |
| 1 | 1600.0000000000000000 |
+----------+-----------------------+
So far so good. So now we need to calculate the difference between these 2 rows. There are a number of different ways to do this, but one is to use a CASE expression to make one of the values negative, and then simply take the SUM of the result (note that I'm using a CTE, but you can also use a sub-query):
WITH
avg_by_wifi(has_wifi, avg_cost) AS
(
SELECT Amenities.wifi, AVG(Billing.price)
FROM Billing
INNER JOIN Amenities ON
Amenities.listing_id = Billing.listing_id
GROUP BY Amenities.wifi
)
SELECT
ABS(SUM
(
CASE
WHEN has_wifi = 1 THEN avg_cost
ELSE -1 * avg_cost
END
))
FROM avg_by_wifi
which gives us the expected value of 200.
Now regarding your data model:
If both your Billing and Amenities table only have 1 row for each listing, it makes sense to combine them into 1 table. For example: Listings(listing_id, price, wifi)
However, this is still problematic, because you probably have a bunch of other amenities you want to model (pool, sauna, etc.) So you might want to model a many-to-many relationship between listings and amenities using an intermediate table:
Listings(listing_id, price)
Amenities(amenity_id, amenity_name)
ListingsAmenities(listing_id, amenity_id)
This way, you could list multiple amenities for a given listing without having to add additional columns. It also becomes easy to store additional information about an amenity: What's the wifi password? How deep is the pool? etc.
Of course, using this model makes your original query (difference in average cost of listings by wifi) a bit tricker, but definitely still doable.
I'm still new and learning in Access vba and appreciate if you can help me with my current scenario.
I have developed a code in VBA which pull the data from a table named Tblsrce
sqlStr = "SELECT zYear, zMonth, Product, Sum(Dollar) as totalAmt FROM Tblsrce "& _
"WHERE fruits IN (NOT NULL, '" & Replace(strFruits, ", ", "', '")
"GROUP BY zYear, zMonth, Product;"
The usual data that the field fruits contains Mango, Apples, Cherry, Banana, etc.
strFruits is a variable that came from users (which is separated by comma if they want to pull more than 1 fruit).
However, I got a problem with it when there are 2 related fruits with different name (e.g. Red Apple and Green Apple) which i need to combine. Is there any way I can Group By those records and tag them as Apples in the current query that i have?
Thanks!
Yes, you could use conditionals like the switch function to calculate some fruit group field.
Switch(
Product='Red Apple', 'Apple'
Product='Green Apple', 'Apple'
Product='Orange', 'Citrus') As ProductGroup
You can then use that field in a higher level query:
Select zYear, zMonth, ProductGroup,
Count(*)
From
(Select f.*,
Switch( .... )
From Fruits f)
Group By zYear, zMonth, ProductGroup
Of course it would be easier if this data isn't calculated dynamically in the query like this, but instead is stored in a separate table, so you know a product group for each of the products. That's also way easier to maintain (just add data instead of modify a query), and probably performs better.
You could, but you would have to have an additional table where you list all fruits, and their groups. Then you can join that in, and group by the groups.
Sample structure:
Fruit | FruitCategory
+-------------+---------------+
| Red apple | Apple |
+-------------+---------------+
| Green apple | Apple |
+-------------+---------------+
| Banana | Banana |
+-------------+---------------+
You can prepopulate the table with a quick SELECT DISTINCT Fruits from Tblsrce and insert that in both columns, and then adjust the categories where you want.
I am trying to write up a query for wordpress which will give me all the post_id's with the lowest fromprice field for each region. Now the trick is these are custom fields in wordpress, and due to such, the information is stored row based, so there is no region and fromprice columns.
So the data I have is (but of course containing a lot more rows):
Post_ID | Meta_Key | Meta_Value
1 | Region | Location1
1 | FromPrice | 150
2 | Region | Location1
2 | FromPrice | 160
3 | Region | Location2
3 | FromPrice | 145
The query I am endeavoring to build should return the post_id of the "lowest priced" matching post grouped by each region with results like:
Post_ID | Region | From Price
1 | Location1 | 150
3 | Location2 | 145
This will allow me to easily iterate the post_id's and print the required information, in fact, I would be just happy with returning post_id's if the rest is harder, I can then fetch the information independently if need be.
Thanks a lot, tearing my hair out over this one; don't often have to think about shifting results on their side from row based to column based that often, but this time I need it!
So you get an idea of the table structure I have, you can use the below as a guide. I thought I had this, but it turned out yes, this query prints out each distinct region WITH the lowest from price found attached to that post in the region, but the post_id is completely incorrect. I don't know why, it seems to be just getting the first result of the post_id and using that.
SELECT pm.post_id,
pm2.meta_value as region,
MIN(pm.meta_value) as price
FROM `wp_postmeta` pm
inner join `wp_postmeta` pm2
on pm2.post_id = pm.post_id
AND pm2.meta_key = 'region'
AND pm.meta_key = 'fromprice'
group by region
I suggest changing MIN(pm.meta_value) in your query to be MIN(CAST(pm.meta_value AS DECIMAL)). Meta_value is a character field, so your existing query will be returning the minimum string value, not the minimum numeric value; for example, "100" will be deemed to be lower than "21".
EDIT - amended CAST syntax.
It's hard to figure out without being able to execute the query, but would it help to just change your group by to:
group by pm.post_id, region
I'm very new to SQL and I hope someone can help me with some SQL syntax. I have a database with these tables and fields,
DATA: data_id, person_id, attribute_id, date, value
PERSONS: person_id, parent_id, name
ATTRIBUTES: attribute_id, attribute_type
attribute_type can be "Height" or "Weight"
Question 1
Give a person's "Name", I would like to return a table of "Weight" measurements for each children. Ie: if John has 3 children names Alice, Bob and Carol, then I want a table like this
| date | Alice | Bob | Carol |
I know how to get a long list of children's weights like this:
select d.date,
d.value
from data d,
persons child,
persons parent,
attributes a
where parent.name='John'
and child.parent_id = parent.person_id
and d.attribute_id = a.attribute_id
and a.attribute_type = "Weight';
but I don't know how to create a new table that looks like:
| date | Child 1 name | Child 2 name | ... | Child N name |
Question 2
Also, I would like to select the attributes to be between a certain range.
Question 3
What happens if the dates are not consistent across the children? For example, suppose Alice is 3 years older than Bob, then there's no data for Bob during the first 3 years of Alice's life. How does the database handle this if we request all the data?
1) It might not be so easy. MS SQL Server can PIVOT a table on an axis, but dumping the resultset to an array and sorting there (assuming this is tied to some sort of program) might be the simpler way right now if you're new to SQL.
If you can manage to do it in SQL it still won't be enough info to create a new table, just return the data you'd use to fill it in, so some sort of external manipulation will probably be required. But you can probably just use INSERT INTO [new table] SELECT [...] to fill that new table from your select query, at least.
2) You can join on attributes for each unique attribute:
SELECT [...] FROM data AS d
JOIN persons AS p ON d.person_id = p.person_id
JOIN attributes AS weight ON p.attribute_id = weight.attribute_id
HAVING weight.attribute_type = 'Weight'
JOIN attributes AS height ON p.attribute_id = height.attribute_id
HAVING height.attribute_type = 'Height'
[...]
(The way you're joining in the original query is just shorthand for [INNER] JOIN .. ON, same thing except you'll need the HAVING clause in there)
3) It depends on the type of JOIN you use to match parent/child relationships, and any dates you're filtering on in the WHERE, if I'm reading that right (entirely possible I'm not). I'm not sure quite what you're looking for, or what kind of database you're using, so no good answer. If you're new enough to SQL that you don't know the different kinds of JOINs and what they can do, it's very worthwhile to learn them - they put the R in RDBMS.
when you do a select, you need to specify the exact columns you want. In other words you can't return the Nth child's name. Ie this isn't possible:
1/2/2010 | Child_1_name | Child_2_name | Child_3_name
1/3/2010 | Child_1_name
1/4/2010 | Child_1_name | Child_2_name
Each record needs to have the same amount of columns. So you might be able to make a select that does this:
1/2/2010 | Child_1_name
1/2/2010 | Child_2_name
1/2/2010 | Child_3_name
1/3/2010 | Child_1_name
1/4/2010 | Child_1_name
1/4/2010 | Child_2_name
And then in a report remap it to how you want it displayed
I need to make a rather complex query, and I need help bad. Below is an example I made.
Basically, I need a query that will return one row for each case_id where the type is support, status start, and date meaning the very first one created (so that in the example below, only the 2/1/2009 John's case gets returned, not the 3/1/2009). The search needs to be dynamic to the point of being able to return all similar rows with different case_id's etc from a table with thousands of rows.
There's more after that but I don't know all the details yet, and I think I can figure it out if you guys (an gals) can help me out here. :)
ID | Case_ID | Name | Date | Status | Type
48 | 450 | John | 6/1/2009 | Fixed | Support
47 | 450 | John | 4/1/2009 | Moved | Support
46 | 451 | Sarah | 3/1/2009 | |
45 | 432 | John | 3/1/2009 | Fixed | Critical
44 | 450 | John | 3/1/2009 | Start | Support
42 | 450 | John | 2/1/2009 | Start | Support
41 | 440 | Ben | 2/1/2009 | |
40 | 432 | John | 1/1/2009 | Start | Critical
...
Thanks a bunch!
Edit:
To answer some people's questions, I'm using SQL Server 2005. And the date is just plain date, not string.
Ok so now I got further in the problem. I ended up with Bliek's solution which worked like a charm. But now I ran into the problem that sometimes the status never starts, as it's solved immediately. I need to include this in as well. But only for a certain time period.
I imagine I'm going to have to check for the case table referenced by FK Case_ID here. So I'd need a way to check for each Case_ID created in the CaseTable within the past month, and then run a search for these in the same table and same manner as posted above, returning only the first result as before. How can I use the other table like that?
As usual I'll try to find the answer myself while waiting, thanks again!
Edit 2:
Seems this is the answer. I don't have access to the full DB yet so I can't fully test it, but it seems to be working with the dummy tables I created, to continue from Bliek's code's WHERE clause:
WHERE RowNumber = 1 AND Case_ID IN (SELECT Case_ID FROM CaseTable
WHERE (Date BETWEEN '2007/11/1' AND '2007/11/30'))
The date's screwed again but you get the idea I'm sure. Thanks for the help everyone! I'll get back if there're more problems, but I think with this info I can improvise my way through most of the SQL problems I currently have to deal with. :)
Maybe something like:
select Case_ID, Name, MIN(date), Status, Type
from table
where type = 'Support'
and status = 'Start'
group by Case_ID, Name, Status, Type
EDIT: You haven't provided a lot of details about what you really want, so I'd suggest that you read all the answers and choose one that suits your problem best. So far I'd say that Tomalak's answer is closest to what you're looking for...
SELECT
c.ID,
c.Case_ID,
c.Name,
c.Date,
c.Status,
c.Type
FROM
CaseTable c
WHERE
c.Type = 'Support'
AND c.Status = 'Start'
AND c.Date = (
SELECT MIN(Date)
FROM CaseTable
WHERE Case_ID = c.Case_ID AND Type = c.Type AND Status = c.Status)
/* GROUP BY only needed when for a given Case_ID several rows
exist that fulfill the WHERE clause */
GROUP BY
c.ID,
c.Case_ID,
c.Name,
c.Date,
c.Status,
c.Type
This query benefits greatly from indexes on the Case_ID, Date, Status and Type columns.
Added value though the fact that the filter on Support and Status only needs to be set in one place.
As an alternative to the GROUP BY clause, you can do SELECT DISTINCT, which would increase readability (this may or may not affect overall performance, I suggest you measure both variants against each other). If you are sure that for no Case_ID in your table two rows exist that have the same Date, you won't need GROUP BY or SELECT DISTINCT at all.
In SQL Server 2005 and beyond I would use Common Table Expressions (CTE). This offers lots of possibilities like so:
With ResultTable (RowNumber
,ID
,Case_ID
,Name
,Date
,Status
,Type)
AS
(
SELECT Row_Number() OVER (PARTITION BY Case_ID
ORDER BY Date ASC)
,ID
,Case_ID
,Name
,Date
,Status
,Type
FROM CaseTable
WHERE Type = 'Support'
AND Status = 'Start'
)
SELECT ID
,Case_ID
,Name
,Date
,Status
,Type
FROM ResultTable
WHERE RowNumber = 1
Don't apologize for your date formatting, it makes more sense that way.
SELECT ID, Case_ID, Name, MIN(Date), Status, Type
FROM caseTable
WHERE Type = 'Support'
AND status = 'Start'
GROUP BY ID, Case_ID, Name, Status, Type