I have the following data from 2 tables Notes (left) and scans (right) :
Imagine the picker and packers were all varying, like you can have JOHN, JANE etc.
I need a query that outputs like so :
On a given date range :
Name - Picked (units) - Packed (units)
MASI - 15 - 21
JOHN - 21 - 32
etc.
I can't figure out how to even start this, any tips will be helpful thanks.
Without a "worker" take that lists each Picker/Packer individually, I think you'd need something like this...
SELECT
CASE WHEN action.name = 'Picker' THEN scans.Picker ELSE scans.Packer END AS worker,
SUM(CASE WHEN action.name = 'Picker' THEN notes.Units ELSE 0 END) AS PickedUnits,
SUM(CASE WHEN action.name = 'Packer' THEN notes.Units ELSE 0 END) AS PackedUnits
FROM
notes
INNER JOIN
scans
ON scans.PickNote = notes.Number
CROSS JOIN
(
SELECT 'Picker' AS name
UNION ALL SELECT 'Packer' AS name
)
AS action
GROUP BY
CASE WHEN action.name = 'Picker' THEN scans.Picker ELSE scans.Packer END
(This is actually just an algebraic re-arrangement of the answer that #RaphaëlAlthaus posted at the same time as me. Both use UNION to work out the Picker values and the Packer values separately. If you have separate indexes on scans.Picker and scans.Packer then I would expect mine MAY be slowest. If you don't have those two indexes then I would expect mine to be fastest. I recommend creating the indexes and testing on a realtisic data set.)
EDIT
Actually, what I would recommend is a change to scans table completely; normalise it.
Your de-normalised set has one row per PickNote, with fields picker and packer.
A normalised set would have two rows per PickNote with fields role and worker.
id | PickNote | Role | Worker
------+----------+------+--------
01 | PK162675 | Pick | MASI
02 | PK162675 | Pack | MASI
03 | PK162676 | Pick | FRED
04 | PK162676 | Pack | JOHN
This allows you to create simple indexes and simple queries.
You may initially baulk at the extra unecessary rows, but it will yield simpler queries, faster queries, better maintainability, increased flexibility, etc, etc.
In short, this normalisation may cost a little extra space, but it pays back dividends forever.
SELECT name, SUM(nbPicked) Picked, SUM(nbPacked) Packed
FROM
(SELECT n.Picker name, SUM(n.Units) nbPicked, 0 nbPacked
FROM Notes n
INNER JOIN scans s ON s.PickNote = n.Number
--WHERE s.ProcessedOn BETWEEN x and y
GROUP BY n.Picker
UNION ALL
SELECT n.Packer name, 0 nbPicked, SUM(n.Units) nbPacked
FROM Notes n
INNER JOIN scans s ON s.PickNote= n.Number
--WHERE s.ProcessedOn BETWEEN x and y
GROUP BY n.Packer)
GROUP BY name;
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.
Hi stackoverflow users
I'm having a bit of a problem trying to combine SUM, MAX and WHERE in one query and after an intense Google search (my search engine skills usually don't fail me) you are my last hope to understand and fix the following issue.
My goal is to count people in a certain period of time and because a person can visit more than once in said period, I'm using MAX. Due to the fact that I'm defining people as male (m) or female (f) using a string (for statistic purposes), CHAR_LENGTH returns the numbers I'm in need of.
SELECT SUM(max_pers) AS "People"
FROM (
SELECT "guests"."id", MAX(CHAR_LENGTH("guests"."gender")) AS "max_pers"
FROM "guests"
GROUP BY "guests"."id")
So far, so good. But now, as stated before, I'd like to only count the guests which visited in a certain time interval (for statistic purposes as well).
SELECT "statistic"."id", SUM(max_pers) AS "People"
FROM (
SELECT "guests"."id", MAX(CHAR_LENGTH("guests"."gender")) AS "max_pers"
FROM "guests"
GROUP BY "guests"."id"),
"statistic", "guests"
WHERE ( "guests"."arrival" <= "statistic"."from" AND "guests"."departure" >= "statistic"."to")
GROUP BY "statistic"."id"
This query returns the following, x = desired result:
x * (x+1)
So if the result should be 3, it's 12. If it should be 5, it's 30 etc.
I probably could solve this algebraic but I'd rather understand what I'm doing wrong and learn from it.
Thanks in advance and I'm certainly going to answer all further questions.
PS: I'm using LibreOffice Base.
EDIT: An example
guests table:
ID | arrival | departure | gender |
10 | 1.1.14 | 10.1.14 | mf |
10 | 15.1.14 | 17.1.14 | m |
11 | 5.1.14 | 6.1.14 | m |
12 | 10.2.14 | 24.2.14 | f |
13 | 27.2.14 | 28.2.14 | mmmmmf |
statistic table:
ID | from | to | name |
1 | 1.1.14 | 31.1.14 |January | expected result: 3
2 | 1.2.14 | 28.2.14 |February| expected result: 7
MAX(...) is the wrong function: You want COUNT(DISTINCT ...).
Add proper join syntax, simplify (and remove unnecessary quotes) and this should work:
SELECT s.id, COUNT(DISTINCT g.id) AS People
FROM statistic s
LEFT JOIN guests g ON g.arrival <= s."from" AND g.departure >= s."too"
GROUP BY s.id
Note: Using LEFT join means you'll get a result of zero for statistics ids that have no guests. If you would rather no row at all, remove the LEFT keyword.
You have a very strange data structure. In any case, I think you want:
SELECT s.id, sum(numpersons) AS People
FROM (select g.id, max(char_length(g.gender)) as numpersons
from guests g join
statistic s
on g.arrival <= s."from" AND g.departure >= s."too"
group by g.id
) g join
GROUP BY s.id;
Thanks for all your inputs. I wasn't familiar with JOIN but it was necessary to solve my problem.
Since my databank is designed in german, I made quite the big mistake while translating it and I'm sorry if this caused confusion.
Selecting guests.id and later on grouping by guests.id wouldn't make any sense since the id is unique. What I actually wanted to do is select and group the guests.adr_id which links a visiting guest to an adress databank.
The correct solution to my problem is the following code:
SELECT statname, SUM (numpers) FROM (
SELECT statistic.name AS statname, guests.adr_id, MAX( CHAR_LENGTH( guests.gender ) ) AS numpers
FROM guests
JOIN statistics ON (guests.arrival <= statistics.too AND guests.departure >= statistics.from )
GROUP BY guests.adr_id, statistic.name )
GROUP BY statname
I also noted that my database structure is a mess but I created it learning by doing and haven't found any time to rewrite it yet. Next time posting, I'll try better.
In my journey to learn SQL, I'm writing various queries on an old database of mine, but getting into more complex things, I want to make sure I'm not over engineering this. I have a table Agent, with different agents offering different prices for cities. Multiple agents can serve the same city, each with different prices. I wanted to run a query which would return the total cost of hiring all of the agents for any given city, ordered by the most expensive.
WITH orderedPrices AS (
SELECT SUM(agtFMPrice)
OVER (PARTITION BY agtCity)
AS IX FROM Agent)
SELECT IX
FROM orderedPrices
ORDER BY IX DESC
I found that doing it without the view returned by orderedPrices, it wouldn't order the prices (I assume because it's an aggregate function, or whatever they're called). Did I do this in the best way I could have, or could it be simplified?
Also, if you're feeling particularly bored, go ahead and give me a new assignment/query to do on this table. I could use the practice.
What you have written in English doesn't seem to quite match qhat you have written in SQL.
English:
- One record per City
- One field per record, showing the total cost of all associated agents
SQL:
- One record per Agent
- One field per record, showing the total cost of all agents in the same city
AgentID | agtCity | agtFMPrice
---------+---------+------------
1 | 1 | 10
2 | 1 | 20
3 | 2 | 30
4 | 2 | 10
5 | 2 | 25
Results of SQL version Results of English version
------------------------ ----------------------------
30 30
30 65
65
65
65
If you want the English version, I'd do this...
SELECT
agtCity,
SUM(agtFMPrice) AS IX
FROM
Agent
GROUP BY
agtCity
ORDER BY
SUM(agtFMPrice) DESC
To assist performance, the table could (should?) also have an Index on (agtCity)
How do I rank salespeople by # customers grouped by department (with ties included)?
For example, given this table, I want to create the Rank column on the right. How should I do this in Access?
SalesPerson Dept #Customers Rank
Bill DeptA 20 1
Ted DeptA 30 2
Jane DeptA 40 3
Bill DeptB 50 1
Mary DeptB 60 2
I already know how to do a simple ranking with this SQL code. But I don't know how to rework this to accept grouping.
Select Count(*) from [Tbl] Where [#Customers] < [Tblx]![#Customers] )+1
Also, there's plenty of answers for this using SQL Server's Rank() function, but I need to do this in Access. Suggestions, please?
SELECT *, (select count(*) from tbl as tbl2 where
tbl.customers > tbl2.customers and tbl.dept = tbl2.dept) + 1 as rank from tbl
Just add the dept field to the subquery...
Great solution with subquery! Except for huge recordsets, the subquery solution gets very slow. Its better(quicker) to use a Self JOIN, look at the folowing solution: self join
SELECT tbl1.SalesPerson , count(*) AS Rank
FROM tbl AS tbl1 INNER JOIN tbl AS tbl2 ON tbl1.DEPT = tbl2.DEPT
AND tbl1.#Customers < tbl2.#Customers
GROUP BY tbl1.SalesPerson
I know this is an old thread. But since I spent a great deal of time on a very similar problem and was greatly helped by the former answers given here, I would like to share what I have found to be a MUCH faster way. (Beware, it is more complicated.)
First make another table called "Individualizer". This will have one field containing a list of numbers 1 through the-highest-rank-that-you-need.
Next create a VBA module and paste this into it:
'Global Declarations Section.
Option Explicit
Global Cntr
'*************************************************************
' Function: Qcntr()
'
' Purpose: This function will increment and return a dynamic
' counter. This function should be called from a query.
'*************************************************************
Function QCntr(x) As Long
Cntr = Cntr + 1
QCntr = Cntr
End Function
'**************************************************************
' Function: SetToZero()
'
' Purpose: This function will reset the global Cntr to 0. This
' function should be called each time before running a query
' containing the Qcntr() function.
'**************************************************************
Function SetToZero()
Cntr = 0
End Function
Save it as Module1.
Next, create Query1 like this:
SELECT Table1.Dept, Count(Table1.Salesperson) AS CountOfSalesperson
FROM Table1
GROUP BY Table1.Dept;
Create a MakeTable query called Query2 like this:
SELECT SetToZero() AS Expr1, QCntr([ID]) AS Rank, Query1.Dept,
Query1.CountOfSalesperson, Individualizer.ID
INTO Qtable1
FROM Query1
INNER JOIN Individualizer
ON Query1.CountOfSalesperson >= Individualizer.ID;
Create another MakeTable query called Query3 like this:
SELECT SetToZero() AS Expr1, QCntr([Identifier]) AS Rank,
[Salesperson] & [Dept] & [#Customers] AS Identifier, Table1.Salesperson,
Table1.Dept, Table1.[#Customers]
INTO Qtable2
FROM Table1;
If you have another field already that uniquely identifies every row you wouldn't need to create an Identifier field.
Run Query2 and Query3 to create the tables.
Create a fourth query called Query4 like this:
SELECT Qtable2.Salesperson, Qtable2.Dept, Qtable2.[#Customers], Qtable1.ID AS Rank
FROM Qtable1
INNER JOIN Qtable2 ON Qtable1.Rank = Qtable2.Rank;
Query4 returns the result you are looking for.
Practically, you would want to write a VBA function to run Query2 and Query3 and then call that function from a button placed in a convenient location.
Now I know this sounds ridiculously complicated for the example you gave. But in real life, I am sure your table is more complicated than this. Hopefully my examples can be applied to your actual situation. In my database with over 12,000 records this method is by FAR the fastest (as in: 6 seconds with 12,000 records compared to over 1 minute with 262 records ranked with the subquery method).
The real secret for me was the MakeTable query because this ranking method is useless unless you immediately output the results to a table. But, this does limit the situations that it can be applied to.
P.S. I forgot to mention that in my database I was not pulling results directly from a table. The records had already gone through a string of queries and multiple calculations before they needed to be ranked. This probably contributed greatly to the huge difference in speed between the two methods in my situation. If you are pulling records directly from a table, you might not notice nearly as big an improvement.
You need to do some math. I typically take advantage of the combination of a counter field and an "offset" field. You're aiming for a table which looks like this (#Customers isn't necessary, but will give you a visual that you're doing it properly):
SalesPerson Dept #Customers Ctr Offset
Bill DeptA 20 1 1
Ted DeptA 30 2 1
Jane DeptA 40 3 1
Bill DeptB 50 4 4
Mary DeptB 60 5 4
So, to give rank, you'd do [Ctr]-[Offset]+1 AS Rank
build a table with SalesPerson, Dept, Ctr, and Offset
insert into that table, ordered by Dept and #Customers (so that they're all sorted properly)
Update Offset to be the MIN(Ctr), grouping on Dept
Perform your math calculation to determine Rank
Clear out the table so you're ready to use it again next time.
To add to this and any other related Access Ranking or Rank Tie Breaker how-tos for other versions of Access, ranking should not be performed on crosstab queries if your FROM clause happens to NOT contain a table but a query that is either a crosstab query or a query that contains within it elsewhere a crosstab query.
The code referenced above where a SELECT statement within a SELECT statment is used (sub query),
"SELECT *, (select count(*) from tbl as tbl2 where tbl.customers > tbl2.customers and tbl.dept = tbl2.dept) + 1 as rank from tbl"
will not work and will always fail expressing a error on portion of the code where "tbl.customers > tbl2.customers" cannot be found.
In my situation on a past project, I was referencing a query instead of a table and within that query I had referenced a crosstab query thus failing and producing an error. I was able to resolve this by creating a table from the crosstab query first, and when I referenced the newly created table in the FROM clause, it started working for me.
So in final, normally you can reference a query or table in the FROM clause of the SELECT statement as what was shared previously above to do ranking, but be carefull as to if you are referencing a query instead of a table, that query must Not be a crosstab query or reference another query that is a crosstab query.
Hope this helps anyone else that may have had problems looking for a possible reason if you happen to reference the statements above and you are not referencing a table in your FROM clause within your own project. Also, performing subqueries on aliases with crosstab queries in Access probably isn't good idea or best practice either so stray away from that if/when possible.
If you found this useful, and wish that Access would allow the use of a scrolling mouse in a passthru query editor, give me a like please.
I normally pick tips and ideas from here and sometimes end up building amazing things from it!
Today, (well let’s say for the past one week), I have been tinkering with Ranking of data in Access and to the best of my ability, I did not anticipate what I was going to do something so complex as to take me a week to figure it out! I picked titbits from two main sites:
https://usefulgyaan.wordpress.com/2013/04/23/ranking-in-ms-access/ (seen that clever ‘>=’ part, and the self joins? Amazing… it helped me to build my solution from just one query, as opposed to the complex method suggested above by asonoftheMighty (not discrediting you… just didn’t want to try it for now; may be when I get to large data I might want to try that as well…)
Right here, from Paul Abott above ( ‘and tbl.dept = tbl2.dept’)… I was lost after ranking because I was placing AND YearID = 1, etc, then the ranking would end up happening only for sub-sets, you guessed right, when YearID = 1! But I had a lot of different scenarios…
Well, I gave that story partly to thank the contributors mentioned, because what I did is to me one of the most complex of the ranking that I think can help you in almost any situation, and since I benefited from others, I would like to share here what I hope may benefit others as well.
Forgive me that I am not able to post my table structures here, it is a lot of related tables. I will only post the query, so if you need to you may develop your tables to end up with that kind of query. But here is my scenario:
You have students in a school. They go through class 1 to 4, can either be in stream A or B, or none when the class is too small. They each take 4 exams (this part is not important now), so you get the total score for my case. That’s it. Huh??
Ok. Lets rank them this way:
We want to know the ranking of
• all students who ever passed through this school (best ever student)
• all students in a particular academic year (student of the year)
• students of a particular class (but remember a student will have passed through all classes, so basically his/her rank in each of those classes for the different years) this is the usual ranking that appears in report cards
• students in their streams (above comment applies)
• I would also like to know the population against which we ranked this student in each category
… all in one table/query. Now you get the point?
(I normally like to do as much of my 'programming' in the database/queries to give me visuals and to reduce the amount of code I will later have to right. I actually won't use this query in my application :), but it let's me know where and how to send my parameters to the query it came from, and what results to expect in my rdlc)
Don't you worry, here it is:
SELECT Sc.StudentID, Sc.StudentName, Sc.Mark,
(SELECT COUNT(Sch.Mark) FROM [StudentScoreRankTermQ] AS Sch WHERE (Sch.Mark >= Sc.Mark)) AS SchoolRank,
(SELECT Count(s.StudentID) FROM StudentScoreRankTermQ AS s) As SchoolTotal,
(SELECT COUNT(Yr.Mark) FROM [StudentScoreRankTermQ] AS Yr WHERE (Yr.Mark >= Sc.Mark) AND (Yr.YearID = Sc.YearID) ) AS YearRank,
(SELECT COUNT(StudentID) FROM StudentScoreRankTermQ AS Yt WHERE (Yt.YearID = Sc.YearID) ) AS YearTotal,
(SELECT COUNT(Cl.Mark) FROM [StudentScoreRankTermQ] AS Cl WHERE (Cl.Mark >= Sc.Mark) AND (Cl.YearID = Sc.YearID) AND (Cl.TermID = Sc.TermID) AND (Cl.ClassID=Sc.ClassID)) AS ClassRank,
(SELECT COUNT(StudentID) FROM StudentScoreRankTermQ AS C WHERE (C.YearID = Sc.YearID) AND (C.TermID = Sc.TermID) AND (C.ClassID = Sc.ClassID) ) AS ClassTotal,
(SELECT COUNT(Str.Mark) FROM [StudentScoreRankTermQ] AS Str WHERE (Str.Mark >= Sc.Mark) AND (Str.YearID = Sc.YearID) AND (Str.TermID = Sc.TermID) AND (Str.ClassID=Sc.ClassID) AND (Str.StreamID = Sc.StreamID) ) AS StreamRank,
(SELECT COUNT(StudentID) FROM StudentScoreRankTermQ AS St WHERE (St.YearID = Sc.YearID) AND (St.TermID = Sc.TermID) AND (St.ClassID = Sc.ClassID) AND (St.StreamID = Sc.StreamID) ) AS StreamTotal,
Sc.CalendarYear, Sc.Term, Sc.ClassNo, Sc.Stream, Sc.StreamID, Sc.YearID, Sc.TermID, Sc.ClassID
FROM StudentScoreRankTermQ AS Sc
ORDER BY Sc.Mark DESC;
You should get something like this:
+-----------+-------------+------+------------+-------------+----------+-----------+-----------+------------+------------+-------------+------+------+-------+--------+
| StudentID | StudentName | Mark | SchoolRank | SchoolTotal | YearRank | YearTotal | ClassRank | ClassTotal | StreamRank | StreamTotal | Year | Term | Class | Stream |
+-----------+-------------+------+------------+-------------+----------+-----------+-----------+------------+------------+-------------+------+------+-------+--------+
| 1 | Jane | 200 | 1 | 20 | 2 | 12 | 1 | 9 | 1 | 5 | 2017 | I | 2 | A |
| 2 | Tom | 199 | 2 | 20 | 1 | 12 | 3 | 9 | 1 | 4 | 2016 | I | 1 | B |
+-----------+-------------+------+------------+-------------+----------+-----------+-----------+------------+------------+-------------+------+------+-------+--------+
Use the separators | to reconstruct the result table
Just an idea about the tables, each student will be related to a class. Each class relates to years. Each stream relates to a class. Each term relates to a year. Each exam relates to a term and student and a class and a year; a student can be in class 1A in 2016 and moves on to class 2b in 2017, etc…
Let me also add that this a beta result, I have not tested it well enough and I do not yet have an opportunity to create a lot of data to see the performance. My first glance at it told me that it is good. So if you find reasons or alerts you want to point my way, please do so in comments so I may keep learning!
I need to keep track of different dates (dynamic). So for a specific Task you could have X number of dates to track (for example DDR1 meeting date, DDR2 meeting date, Due Date, etc).
My strategy was to create one table (DateTypeID, DateDescription) which would store the description of each date. Then I could create the main table (ID, TaskDescription, DateTypeID). So all the dates would be in one column and you could tell what that date represents by looking at the TypeID. The problem is displaying it in a grid. I know I should use a cross tab query, but i cannot get it to work. For example, I use a Case statement in SQL Server 2000 to pivot the table over so that each column name is the name of the date type. IF we have the following tables:
DateType Table
DateTypeID | DateDescription
1 | DDR1
2 | DDR2
3 | DueDate
Tasks Table
ID | TaskDescription
1 | Create Design
2 | Submit Paperwork
Tasks_DateType Table
TasksID | DateTypeID | Date
1 | 1 | 09/09/2009
1 | 2 | 10/10/2009
2 | 1 | 11/11/2009
2 | 3 | 12/12/2009
THE RESULT SHOULD BE:
TaskDescription | DDr1 | DDR2 | DueDate
Create Design |09/09/2009 | 10/10/2009 | null
Submit Paperwork |11/11/2009 | null | 12/12/2009
IF anyone has any idea how I can go about researching this, I appreciate it. The reason I do this instead of making a column for each date, has to do with the ability to let the user in the future add as many dates as they want without having to manually add columns to the table and editing html code. This also allows simple code for comparing dates or show upcoming tasks by their type (ex. 'Create design's DDR1 date is coming up' ) If anyone can point me in the right direction, I appreciate it.
Here is a proper answer, tested with your data. I only used the first two date types, but you'd build this up on the fly anyway.
Select
Tasks.TaskDescription,
Min(Case DateType.DateDescription When 'DDR1' Then Tasks_DateType.Date End) As DDR1,
Min(Case DateType.DateDescription When 'DDR2' Then Tasks_DateType.Date End) As DDR2
From
Tasks_DateType
INNER JOIN Tasks ON Tasks_DateType.TaskID = Tasks.TaskID
INNER JOIN DateType ON Tasks_DateType.DateTypeID = DateType.DateTypeID
Group By
Tasks.TaskDescription
EDIT
van mentioned that tasks with no dates won't show up. This is correct. Using left joins (again, mentioned by van) and restructuring the query a bit will return all tasks, even though this is not your need at the moment.
Select
Tasks.TaskDescription,
Min(Case DateType.DateDescription When 'DDR1' Then Tasks_DateType.Date End) As DDR1,
Min(Case DateType.DateDescription When 'DDR2' Then Tasks_DateType.Date End) As DDR2
From
Tasks
LEFT OUTER JOIN Tasks_DateType ON Tasks_DateType.TaskID = Tasks.TaskID
LEFT OUTER JOIN DateType ON Tasks_DateType.DateTypeID = DateType.DateTypeID
Group By
Tasks.TaskDescription
If the pivoted columns are unknown (dynamic), then you'll have to build up your query manually in either ms-sql 2000 or 2005, ie with out without PIVOT.
This involves either executing dynamic sql in a stored procedure (generally a no-no) or querying a view with dynamic sql. The latter is the approach I generally go with.
For pivoting, I prefer the Rozenshtein method over case statements, as explained here:
http://www.stephenforte.net/PermaLink.aspx?guid=2b0532fc-4318-4ac0-a405-15d6d813eeb8
EDIT
You can also do this in linq-to-sql, but it emits some pretty inefficient code (at least when I view it through linqpad), so I don't recommend it. If you're still curious I can post an example of how to do it.
I don't have personal experience with the pivot operator, it may provide a better solution.
But I've used a case statement in the past
SELECT
TaskDescription,
CASE(DateTypeID = 1, Tasks_DateType.Date) AS DDr1,
CASE(DateTypeID = 2, Tasks_DateType.Date) AS DDr2,
...
FROM Tasks
INNER JOIN Tasks_DateType ON Tasks.ID = Tasks_DateType.TasksID
INNER JOIN DateType ON Tasks_DateType.DateTypeID = DateType.DateTypeID
GROUP BY TaskDescription
This will work, but will require you to change the SQL whenever there are more Task descriptions added, so it's not ideal.
EDIT:
It appears as though the PIVOT keyword was added in SqlServer 2005, this example shows how to do a pivot query in both 2000 & 2005, but it is similar to my answer.
Version-1: +simple, -must be changed every time DateType is added. So is not great for a dynamic solution:
SELECT tt.ID,
tt.TaskDescription,
td1.Date AS DDR1,
td2.Date AS DDR2,
td3.Date AS DueDate
FROM Tasks tt
LEFT JOIN Tasks_DateType td1
ON td1.TasksID = tt.ID AND td1.DateTypeID = 1
LEFT JOIN Tasks_DateType td2
ON td2.TasksID = tt.ID AND td2.DateTypeID = 2
LEFT JOIN Tasks_DateType td3
ON td3.TasksID = tt.ID AND td3.DateTypeID = 3
Version-2: completely dynamic (with some limitations, but they can be handled - just google for it):
Dynamic pivot query creation. See Dynamic Cross-Tabs/Pivot Tables: you need to create one SP of UDF and then can use it for multiple purposes. This is the original post, to which you may find many links and improvements.
Version-3: just leave it for your client code to handle. I would not design my SQL to return a dynamic set of data, but rather handle it on the client (presentation layer). I just would not like to handle some dynamic columns that come as a result of my query, where I need to guess what is that exactly. The only reason I use Version-2 is when the result is presented directly as a table for a report. In all other cases for truly dynamic data I use client code. For example: having structure you have, how will you attach logic that field DueDate is mandatory - you cannot use DB constraints; how will you ensure that DDR1 is not higher then DDR2? If these are not separate (static) columns in the database (where you can use CONSTRAINTS), then the client code is the one that validates your data consistency.
Good luck!