A brief explanation on the relevant domain part:
A Category is composed of four data:
Gender (Male/Female)
Age Division (Mighty Mite to Master)
Belt Color (White to Black)
Weight Division (Rooster to Heavy)
So, Male Adult Black Rooster forms one category. Some combinations may not exist, such as mighty mite black belt.
An Athlete fights Athletes of the same Category, and if he classifies, he fights Athletes of different Weight Divisions (but of the same Gender, Age and Belt).
To the modeling. I have a Category table, already populated with all combinations that exists in the domain.
CREATE TABLE Category (
[Id] [int] IDENTITY(1,1) NOT NULL,
[AgeDivision_Id] [int] NULL,
[Gender] [int] NULL,
[BeltColor] [int] NULL,
[WeightDivision] [int] NULL
)
A CategorySet and a CategorySet_Category, which forms a many to many relationship with Category.
CREATE TABLE CategorySet (
[Id] [int] IDENTITY(1,1) NOT NULL,
[Championship_Id] [int] NOT NULL,
)
CREATE TABLE CategorySet_Category (
[CategorySet_Id] [int] NOT NULL,
[Category_Id] [int] NOT NULL
)
Given the following result set:
| Options_Id | Championship_Id | AgeDivision_Id | BeltColor | Gender | WeightDivision |
|------------|-----------------|----------------|-----------|--------|----------------|
1. | 2963 | 422 | 15 | 7 | 0 | 0 |
2. | 2963 | 422 | 15 | 7 | 0 | 1 |
3. | 2963 | 422 | 15 | 7 | 0 | 2 |
4. | 2963 | 422 | 15 | 7 | 0 | 3 |
5. | 2964 | 422 | 15 | 8 | 0 | 0 |
6. | 2964 | 422 | 15 | 8 | 0 | 1 |
7. | 2964 | 422 | 15 | 8 | 0 | 2 |
8. | 2964 | 422 | 15 | 8 | 0 | 3 |
Because athletes may fight two CategorySets, I need CategorySet and CategorySet_Category to be populated in two different ways (it can be two queries):
One Category_Set for each row, with one CategorySet_Category pointing to the corresponding Category.
One Category_Set that groups all WeightDivisions in one CategorySet in the same AgeDivision_Id, BeltColor, Gender. In this example, only BeltColor varies.
So the final result would have a total of 10 CategorySet rows:
| Id | Championship_Id |
|----|-----------------|
| 1 | 422 |
| 2 | 422 |
| 3 | 422 |
| 4 | 422 |
| 5 | 422 |
| 6 | 422 |
| 7 | 422 |
| 8 | 422 |
| 9 | 422 | /* groups different Weight Division for BeltColor 7 */
| 10 | 422 | /* groups different Weight Division for BeltColor 8 */
And CategorySet_Category would have 16 rows:
| CategorySet_Id | Category_Id |
|----------------|-------------|
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 4 | 4 |
| 5 | 5 |
| 6 | 6 |
| 7 | 7 |
| 8 | 8 |
| 9 | 1 | /* groups different Weight Division for BeltColor 7 */
| 9 | 2 | /* groups different Weight Division for BeltColor 7 */
| 9 | 3 | /* groups different Weight Division for BeltColor 7 */
| 9 | 4 | /* groups different Weight Division for BeltColor 7 */
| 10 | 5 | /* groups different Weight Division for BeltColor 8 */
| 10 | 6 | /* groups different Weight Division for BeltColor 8 */
| 10 | 7 | /* groups different Weight Division for BeltColor 8 */
| 10 | 8 | /* groups different Weight Division for BeltColor 8 */
I have no idea how to insert into CategorySet, grab it's generated Id, then use it to insert into CategorySet_Category
I hope I've made my intentions clear.
I've also created a SQLFiddle.
Edit 1: I commented in Jacek's answer that this would run only once, but this is false. It will run a couple of times a week. I have the option to run as SQL Command from C# or a stored procedure. Performance is not crucial.
Edit 2: Jacek suggested using SCOPE_IDENTITY to return the Id. Problem is, SCOPE_IDENTITY returns only the last inserted Id, and I insert more than one row in CategorySet.
Edit 3: Answer to #FutbolFan who asked how the FakeResultSet is retrieved.
It is a table CategoriesOption (Id, Price_Id, MaxAthletesByTeam)
And tables CategoriesOptionBeltColor, CategoriesOptionAgeDivision, CategoriesOptionWeightDivison, CategoriesOptionGender. Those four tables are basically the same (Id, CategoriesOption_Id, Value).
The query look like this:
SELECT * FROM CategoriesOption co
LEFT JOIN CategoriesOptionAgeDivision ON
CategoriesOptionAgeDivision.CategoriesOption_Id = co.Id
LEFT JOIN CategoriesOptionBeltColor ON
CategoriesOptionBeltColor.CategoriesOption_Id = co.Id
LEFT JOIN CategoriesOptionGender ON
CategoriesOptionGender.CategoriesOption_Id = co.Id
LEFT JOIN CategoriesOptionWeightDivision ON
CategoriesOptionWeightDivision.CategoriesOption_Id = co.Id
The solution described here will work correctly in multi-user environment and when destination tables CategorySet and CategorySet_Category are not empty.
I used schema and sample data from your SQL Fiddle.
First part is straight-forward
(ab)use MERGE with OUTPUT clause.
MERGE can INSERT, UPDATE and DELETE rows. In our case we need only to INSERT. 1=0 is always false, so the NOT MATCHED BY TARGET part is always executed. In general, there could be other branches, see docs. WHEN MATCHED is usually used to UPDATE; WHEN NOT MATCHED BY SOURCE is usually used to DELETE, but we don't need them here.
This convoluted form of MERGE is equivalent to simple INSERT, but unlike simple INSERT its OUTPUT clause allows to refer to the columns that we need.
MERGE INTO CategorySet
USING
(
SELECT
FakeResultSet.Championship_Id
,FakeResultSet.Price_Id
,FakeResultSet.MaxAthletesByTeam
,Category.Id AS Category_Id
FROM
FakeResultSet
INNER JOIN Category ON
Category.AgeDivision_Id = FakeResultSet.AgeDivision_Id AND
Category.Gender = FakeResultSet.Gender AND
Category.BeltColor = FakeResultSet.BeltColor AND
Category.WeightDivision = FakeResultSet.WeightDivision
) AS Src
ON 1 = 0
WHEN NOT MATCHED BY TARGET THEN
INSERT
(Championship_Id
,Price_Id
,MaxAthletesByTeam)
VALUES
(Src.Championship_Id
,Src.Price_Id
,Src.MaxAthletesByTeam)
OUTPUT inserted.id AS CategorySet_Id, Src.Category_Id
INTO CategorySet_Category (CategorySet_Id, Category_Id)
;
FakeResultSet is joined with Category to get Category.id for each row of FakeResultSet. It is assumed that Category has unique combinations of AgeDivision_Id, Gender, BeltColor, WeightDivision.
In OUTPUT clause we need columns from both source and destination tables. The OUTPUT clause in simple INSERT statement doesn't provide them, so we use MERGE here that does.
The MERGE query above would insert 8 rows into CategorySet and insert 8 rows into CategorySet_Category using generated IDs.
Second part
needs temporary table. I'll use a table variable to store generated IDs.
DECLARE #T TABLE (
CategorySet_Id int
,AgeDivision_Id int
,Gender int
,BeltColor int);
We need to remember the generated CategorySet_Id together with the combination of AgeDivision_Id, Gender, BeltColor that caused it.
MERGE INTO CategorySet
USING
(
SELECT
FakeResultSet.Championship_Id
,FakeResultSet.Price_Id
,FakeResultSet.MaxAthletesByTeam
,FakeResultSet.AgeDivision_Id
,FakeResultSet.Gender
,FakeResultSet.BeltColor
FROM
FakeResultSet
GROUP BY
FakeResultSet.Championship_Id
,FakeResultSet.Price_Id
,FakeResultSet.MaxAthletesByTeam
,FakeResultSet.AgeDivision_Id
,FakeResultSet.Gender
,FakeResultSet.BeltColor
) AS Src
ON 1 = 0
WHEN NOT MATCHED BY TARGET THEN
INSERT
(Championship_Id
,Price_Id
,MaxAthletesByTeam)
VALUES
(Src.Championship_Id
,Src.Price_Id
,Src.MaxAthletesByTeam)
OUTPUT
inserted.id AS CategorySet_Id
,Src.AgeDivision_Id
,Src.Gender
,Src.BeltColor
INTO #T(CategorySet_Id, AgeDivision_Id, Gender, BeltColor)
;
The MERGE above would group FakeResultSet as needed and insert 2 rows into CategorySet and 2 rows into #T.
Then join #T with Category to get Category.IDs:
INSERT INTO CategorySet_Category (CategorySet_Id, Category_Id)
SELECT
TT.CategorySet_Id
,Category.Id AS Category_Id
FROM
#T AS TT
INNER JOIN Category ON
Category.AgeDivision_Id = TT.AgeDivision_Id AND
Category.Gender = TT.Gender AND
Category.BeltColor = TT.BeltColor
;
This will insert 8 rows into CategorySet_Category.
Here is not the full answer, but direction which you can use to solve this:
1st query:
select row_number() over(order by t, Id) as n, Championship_Id
from (
select distinct 0 as t, b.Id, a.Championship_Id
from FakeResultSet as a
inner join
Category as b
on
a.AgeDivision_Id=b.AgeDivision_Id and
a.Gender=b.Gender and
a.BeltColor=b.BeltColor and
a.WeightDivision=b.WeightDivision
union all
select distinct 1, BeltColor, Championship_Id
from FakeResultSet
) as q
2nd query:
select q2.CategorySet_Id, c.Id as Category_Id from (
select row_number() over(order by t, Id) as CategorySet_Id, Id, BeltColor
from (
select distinct 0 as t, b.Id, null as BeltColor
from FakeResultSet as a
inner join
Category as b
on
a.AgeDivision_Id=b.AgeDivision_Id and
a.Gender=b.Gender and
a.BeltColor=b.BeltColor and
a.WeightDivision=b.WeightDivision
union all
select distinct 1, BeltColor, BeltColor
from FakeResultSet
) as q
) as q2
inner join
Category as c
on
(q2.BeltColor is null and q2.Id=c.Id)
OR
(q2.BeltColor = c.BeltColor)
of course this will work only for empty CategorySet and CategorySet_Category tables, but you can use select coalese(max(Id), 0) from CategorySet to get current number and add it to row_number, thus you will get real ID which will be inserted into CategorySet row for second query
What I do when I run into these situations is to create one or many temporary tables with row_number() over clauses giving me identities on the temporary tables. Then I check for the existence of each record in the actual tables, and if they exist update the temporary table with the actual record ids. Finally I run a while exists loop on the temporary table records missing the actual id and insert them one at a time, after the insert I update the temporary table record with the actual ids. This lets you work through all the data in a controlled manner.
##IDENTITY is your friend to the 2nd part of question
https://msdn.microsoft.com/en-us/library/ms187342.aspx
and
Best way to get identity of inserted row?
Some API (drivers) returns int from update() function, i.e. ID if it is "insert". What API/environment do You use?
I don't understand 1st problem. You should not insert identity column.
Below query will give final result For CategorySet rows:
SELECT
ROW_NUMBER () OVER (PARTITION BY Championship_Id ORDER BY Championship_Id) RNK,
Championship_Id
FROM
(
SELECT
Championship_Id
,BeltColor
FROM #FakeResultSet
UNION ALL
SELECT
Championship_Id,BeltColor
FROM #FakeResultSet
GROUP BY Championship_Id,BeltColor
)BASE
Related
I have a structure / tree that looks similar to this.
CostType is mandatory and can exist by itself, but it can have a parent ProfitType or Unit and other CostTypes as children.
There can only be duplicate Units. Other cannot appear multiple times in the structure.
| ID | name | parent_id | ProfitType | CostType | Unit |
| -: | ------------- | --------: |
| 1 | Root | (NULL) |
| 2 | 1 | 1 | 300 | | |
| 3 | 1-1 | 2 | | 111 | |
| 4 | 1-1-1 | 3 | | | 8 |
| 5 | 1-2 | 2 | | 222 | |
| 6 | 1-2-1 | 5 | | 333 | |
| 7 | 1-2-1-1 | 6 | | | 8 |
| 8 | 1-2-1-2 | 6 | | | 9 |
Parameters | should RETURN |
(300,111,8) | 4 |
(null,111,8) | 4 |
(null,null,8) | first match, 4 |
(null,222,8) | best match, 5 |
(null,333,null) | 6 |
I am at a loss on how I could create a function that receives (ProfitType, CostType, Unit) and return the best matching ID from the structure.
This isn't giving exactly the answers you provided as example, but see my comment above - if (null,222,8) should be 7 to match how (null,333,8) returns 4 then this is correct.
Also note that I formatted this using temp tables instead of as a function, I don't want to trip a schema change audit so I posted what I have as temp tables, I can rewrite it as a function Monday when my DBA is available, but I thought you might need it before the weekend. Just edit the "DECLARE #ProfitType int = ..." lines to the values you want to test
I also put in quite a few comments because the logic is tricky, but if they aren't enough leave a comment and I can expand my explanation
/*
ASSUMPTIONS:
A tree can be of arbitrary depth, but will not exceed the recursion limit (defaults to 100)
All trees will include at least 1 CostType
All trees will have at most 1 ProfitType
CostType can appear multiple times in a traversal from root to leaf (can units?)
*/
SELECT *
INTO #Temp
FROM (VALUES (1,'Root',NULL, NULL, NULL, NULL)
, (2,'1', 1, 300, NULL, NULL)
, (3,'1-1', 2, NULL, 111, NULL)
, (4,'1-1-1', 3, NULL, NULL, 8)
, (5,'1-2', 2, NULL, 222, NULL)
, (6,'1-2-1', 5, NULL, 333, NULL)
, (7,'1-2-1-1', 6, NULL, NULL, 8)
, (8,'1-2-1-2', 6, NULL, NULL, 9)
) as TempTable(ID, RName, Parent_ID, ProfitType, CostType, UnitID)
--SELECT * FROM #Temp
DECLARE #ProfitType int = NULL--300
DECLARE #CostType INT = 333 --NULL --111
DECLARE #UnitID INT = NULL--8
--SELECT * FROM #Temp
;WITH cteMatches as (
--Start with all nodes that match one criteria, default a score of 100
SELECT N.ID as ReportID, *, 100 as Score, 1 as Depth
FROM #Temp AS N
WHERE N.CostType= #CostType OR N.ProfitType=#ProfitType OR N.UnitID = #UnitID
), cteEval as (
--This is a recursive CTE, it has a (default) limit of 100 recursions
--, but that can be raised if your trees are deeper than 100 nodes
--Start with the base case
SELECT M.ReportID, M.RName, M.ID ,M.Parent_ID, M.Score
, M.Depth, M.ProfitType , M.CostType , M.UnitID
FROM cteMatches as M
UNION ALL
--This is the recursive part, add to the list of matches the match when
--its immediate parent is also considered. For that match increase the score
--if the parent contributes another match. Also update the ID of the match
--to the parent's IDs so recursion can keep adding if more matches are found
SELECT M.ReportID, M.RName, N.ID ,N.Parent_ID
, M.Score + CASE WHEN N.CostType= #CostType
OR N.ProfitType=#ProfitType
OR N.UnitID = #UnitID THEN 100 ELSE 0 END as Score
, M.Depth + 1, N.ProfitType , N.CostType , N.UnitID
FROM cteEval as M INNER JOIN #Temp AS N on M.Parent_ID = N.ID
)SELECT TOP 1 * --Drop the "TOP 1 *" to see debugging info (runners up)
FROM cteEval
ORDER BY SCORE DESC, DEPTH
DROP TABLE #Temp
I'm sorry I don't have enough rep to comment.
You'll have to define "best answer" (for example, why isn't the answer to null,222,8 7 or null instead of 5?), but here's the approach I'd use:
Derive a new table where ProfitType and CostType are listed explicitly instead of only by inheritance. I would approach that by using a cursor (how awful, I know) and following the parent_id until a ProfitType and CostType is found -- or the root is reached. This presumes an unlimited amount of child/grandchild levels for parent_id. If there is a limit, then you can instead use N self joins where N is the number of parent_id levels allowed.
Then you run multiple queries against the derived table. The first query would be for an exact match (and then exit if found). Then next query would be for the "best" partial match (then exit if found), followed by queries for 2nd best, 3rd best, etc. until you've exhausted your "best" match criteria.
If you need nested parent CostTypes to be part of the "best match" criteria, then I would make duplicate entries in the derived table for each row that has multiple CostTypes with a CostType "level". level 1 is the actual CostType. level 2 is that CostType's parent, level 3 etc. Then your best match queries would return multiple rows and you'd need to pick the row with the lowest level (which is the closest parent/grandparent).
I have a schema like the following in Oracle
Section:
+--------+----------+
| sec_ID | group_ID |
+--------+----------+
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 2 |
+--------+----------+
Section_to_Item:
+--------+---------+
| sec_ID | item_ID |
+--------+---------+
| 1 | 1 |
| 1 | 2 |
| 2 | 3 |
| 2 | 4 |
+--------+---------+
Item:
+---------+------+
| item_ID | data |
+---------+------+
| 1 | a |
| 2 | b |
| 3 | c |
| 4 | d |
+---------+------+
Item_Version:
+---------+----------+--------+
| item_ID | start_ID | end_ID |
+---------+----------+--------+
| 1 | 1 | |
| 2 | 1 | 3 |
| 3 | 2 | |
| 4 | 1 | 2 |
+---------+----------+--------+
Section_to_Item has FK into Section and Item on the *_ID columns.
Item_version is indexed on item_ID but has no FK to Item.item_ID (ran out of space in the snapshot group).
I have code that receives a list of version IDs and I want to get all items in sections in a given group that are valid for at least one of the versions passed in. If an item has no end_ID, it's valid for anything starting with start_ID. If it has an end_id, it's valid for anything up until (not including) end_ID.
What I currently have is:
SELECT Items.data
FROM Section, Section_to_Items, Item, Item_Version
WHERE Section.group_ID = 1
AND Section_to_Item.sec_ID = Section.sec_ID
AND Item.item_ID = Section_to_Item.item_ID
AND Item.item_ID = Item_Version.item_ID
AND exists (
SELECT *
FROM (
SELECT 2 AS version FROM DUAL
UNION ALL SELECT 3 AS version FROM DUAL
) passed_versions
WHERE Item_Version.start_ID <= passed_versions.version
AND (Item_Version.end_ID IS NULL or Item_Version.end_ID > passed_version.version)
)
Note that the UNION ALL statement is dynamically generated from the list of passed in versions.
This query currently does a cartesian join and is very slow.
For some reason, if I change the query to join
AND Item_Version.item_ID = Section_to_Item.item_ID
which is not a FK, the query does not do the cartesian join and is much faster.
A) Can anyone explain why this is?
B) Is this the right way to be joining this sequence of tables (I feel weird about joining Item.item_ID to two different tables)
C) Is this the right way to get versions between start_ID and end_ID?
Edit
Same query with inner join syntax:
SELECT Items.data
FROM Item
INNER JOIN Section_to_Items ON Section_to_Items.item_ID = Item.item_ID
INNER JOIN Section ON Section.sec_ID = Section_to_Items.sec_ID
INNER JOIN Item_Version ON Item_Version.item_ID = Item_.item_ID
WHERE Section.group_ID = 1
AND exists (
SELECT *
FROM (
SELECT 2 AS version FROM DUAL
UNION ALL SELECT 3 AS version FROM DUAL
) passed_versions
WHERE Item_Version.start_ID <= passed_versions.version
AND (Item_Version.end_ID IS NULL or Item_Version.end_ID > passed_version.version)
)
Note that in this case the performance difference comes from joining on Item_Version first and then joining Section_to_Item on Item_Version.item_ID.
In terms of table size, Section_to_Item, Item, and Item_Version should be similar (1000s) while Section should be small.
Edit
I just found out that apparently, the schema has no FKs. The FKs specified in the schema configuration files are ignored. They're just there for documentation. So there's no difference between joining on a FK column or not. That being said, by changing the joins into a cascade of SELECT INs, I'm able to avoid joining the entire Item table twice. I don't love the resulting query, and I don't really understand the difference, but the stats indicate it's much less work (changes the A-Rows returned from the inner most scan on Section from 656,000 to 488 (it used to be 656k starts returning 1 row, now it's 488 starts returning 1 row)).
Edit
It turned out to be stale statistics - the two queries were equivalent the whole time but with the incomplete statistics, the DB happened to notice the correct plan only in the second instance. After updating statistics, both queries generated the same plan.
I'm not sure if this is the best idea but this seems to avoid the cartesian join:
select data
from Item
where item_ID in (
select item_ID
from Item_Version
where item_ID in (
select item_ID
from Section_to_Item
where sec_ID in (
select sec_ID
from Section
where group_ID = 1
)
)
and exists (
select 1
from (
select 2 as version
from dual
union all
select 3 as version
from dual
) versions
where versions.version >= start_ID
and (end_ID is null or versions.version <)
)
)
I have performing some queries using PostgreSQL SELECT DISTINCT ON syntax. I would like to have the query return the total number of rows alongside with every result row.
Assume I have a table my_table like the following:
CREATE TABLE my_table(
id int,
my_field text,
id_reference bigint
);
I then have a couple of values:
id | my_field | id_reference
----+----------+--------------
1 | a | 1
1 | b | 2
2 | a | 3
2 | c | 4
3 | x | 5
Basically my_table contains some versioned data. The id_reference is a reference to a global version of the database. Every change to the database will increase the global version number and changes will always add new rows to the tables (instead of updating/deleting values) and they will insert the new version number.
My goal is to perform a query that will only retrieve the latest values in the table, alongside with the total number of rows.
For example, in the above case I would like to retrieve the following output:
| total | id | my_field | id_reference |
+-------+----+----------+--------------+
| 3 | 1 | b | 2 |
+-------+----+----------+--------------+
| 3 | 2 | c | 4 |
+-------+----+----------+--------------+
| 3 | 3 | x | 5 |
+-------+----+----------+--------------+
My attemp is the following:
select distinct on (id)
count(*) over () as total,
*
from my_table
order by id, id_reference desc
This returns almost the correct output, except that total is the number of rows in my_table instead of being the number of rows of the resulting query:
total | id | my_field | id_reference
-------+----+----------+--------------
5 | 1 | b | 2
5 | 2 | c | 4
5 | 3 | x | 5
(3 rows)
As you can see it has 5 instead of the expected 3.
I can fix this by using a subquery and count as an aggregate function:
with my_values as (
select distinct on (id)
*
from my_table
order by id, id_reference desc
)
select count(*) over (), * from my_values
Which produces my expected output.
My question: is there a way to avoid using this subquery and have something similar to count(*) over () return the result I want?
You are looking at my_table 3 ways:
to find the latest id_reference for each id
to find my_field for the latest id_reference for each id
to count the distinct number of ids in the table
I therefore prefer this solution:
select
c.id_count as total,
a.id,
a.my_field,
b.max_id_reference
from
my_table a
join
(
select
id,
max(id_reference) as max_id_reference
from
my_table
group by
id
) b
on
a.id = b.id and
a.id_reference = b.max_id_reference
join
(
select
count(distinct id) as id_count
from
my_table
) c
on true;
This is a bit longer (especially the long thin way I write SQL) but it makes it clear what is happening. If you come back to it in a few months time (somebody usually does) then it will take less time to understand what is going on.
The "on true" at the end is a deliberate cartesian product because there can only ever be exactly one result from the subquery "c" and you do want a cartesian product with that.
There is nothing necessarily wrong with subqueries.
I have an "insert only" database, wherein records aren't physically updated, but rather logically updated by adding a new record, with a CRUD value, carrying a larger sequence. In this case, the "seq" (sequence) column is more in line with what you may consider a primary key, but the "id" is the logical identifier for the record. In the example below,
This is the physical representation of the table:
seq id name | CRUD |
----|-----|--------|------|
1 | 10 | john | C |
2 | 10 | joe | U |
3 | 11 | kent | C |
4 | 12 | katie | C |
5 | 12 | sue | U |
6 | 13 | jill | C |
7 | 14 | bill | C |
This is the logical representation of the table, considering the "most recent" records:
seq id name | CRUD |
----|-----|--------|------|
2 | 10 | joe | U |
3 | 11 | kent | C |
5 | 12 | sue | U |
6 | 13 | jill | C |
7 | 14 | bill | C |
In order to, for instance, retrieve the most recent record for the person with id=12, I would currently do something like this:
SELECT
*
FROM
PEOPLE P
WHERE
P.ID = 12
AND
P.SEQ = (
SELECT
MAX(P1.SEQ)
FROM
PEOPLE P1
WHERE P.ID = 12
)
...and I would receive this row:
seq id name | CRUD |
----|-----|--------|------|
5 | 12 | sue | U |
What I'd rather do is something like this:
WITH
NEW_P
AS
(
--CTE representing all of the most recent records
--i.e. for any given id, the most recent sequence
)
SELECT
*
FROM
NEW_P P2
WHERE
P2.ID = 12
The first SQL example using the the subquery already works for us.
Question: How can I leverage a CTE to simplify our predicates when needing to leverage the "most recent" logical view of the table. In essence, I don't want to inline a subquery every single time I want to get at the most recent record. I'd rather define a CTE and leverage that in any subsequent predicate.
P.S. While I'm currently using DB2, I'm looking for a solution that is database agnostic.
This is a clear case for window (or OLAP) functions, which are supported by all modern SQL databases. For example:
WITH
ORD_P
AS
(
SELECT p.*, ROW_NUMBER() OVER ( PARTITION BY id ORDER BY seq DESC) rn
FROM people p
)
,
NEW_P
AS
(
SELECT * from ORD_P
WHERE rn = 1
)
SELECT
*
FROM
NEW_P P2
WHERE
P2.ID = 12
PS. Not tested. You may need to explicitly list all columns in the CTE clauses.
I guess you already put it together. First find the max seq associated with each id, then use that to join back to the main table:
WITH newp AS (
SELECT id, MAX(seq) AS latestseq
FROM people
GROUP BY id
)
SELECT p.*
FROM people p
JOIN newp n ON (n.latestseq = p.seq)
ORDER BY p.id
What you originally had would work, or moving the CTE into the "from" clause. Maybe you want to use a timestamp field rather than a sequence number for the ordering?
Following up from #Glenn's answer, here is an updated query which meets my original goal and is on par with #mustaccio's answer, but I'm still not sure what the performance (and other) implications of this approach vs the other are.
WITH
LATEST_PERSON_SEQS AS
(
SELECT
ID,
MAX(SEQ) AS LATEST_SEQ
FROM
PERSON
GROUP BY
ID
)
,
LATEST_PERSON AS
(
SELECT
P.*
FROM
PERSON P
JOIN
LATEST_PERSON_SEQS L
ON
(
L.LATEST_SEQ = P.SEQ)
)
SELECT
*
FROM
LATEST_PERSON L2
WHERE
L2.ID = 12
I have a table Farm with these columns
FarmID:(primary)
Kenizy:
BarBedo:
BarBodo:
MorKodo:
These columns are palm types in some language. each column of those contains a number indicates the number of this type of palm inside a farm.
Example:
FarmID | Kenizy | BarBedo | BarBodo | MorKodo
-----------------------------------------------
3 | 20 | 12 | 45 | 60
22 | 21 | 9 | 41 | 3
I want to insert that table into the following tables:
Table Palm_Farm
FarmID:(primary)
PalmID;(primary)
PalmTypeName:
Count:
That table connects each farm with each palm type.
Example:
FarmID | PalmID | PalmTypeName | Count
-----------------------------------------------
3 | 1 | Kenizy | 20
3 | 2 | BarBedo | 12
3 | 3 | BarBodo | 45
3 | 4 | MorKodo | 60
22 | 1 | Kenizy | 21
22 | 2 | BarBedo | 9
22 | 3 | BarBodo | 41
22 | 4 | MorKodo | 3
I have to use the following table Palms in order to take the PalmID column.
PalmID:(primary)
PlamTypeName:
...other not important columns
This table is to save information about each palm type.
Example:
PalmID | PlamTypeName
-------------------------
1 | Kenizy
2 | BarBedo
3 | BarBodo
4 | MorKodo
The PalmTypeName column has the value the same as the COLUMN NAMES in the Farm table.
So my question is:
How to insert the data from Farm table to Palm_Farm considering that the PalmID exist in the Palm table
I hope I could make my question clear, I tried to solve my problem myself but the fact that the column name in the Farm table must be the column value in the Palm_Farm table couldn't know how to do it.
I can't change the table structure because we are trying to help a customer with this already existing tables
I am using SQL Server 2008 so Merge is welcomed.
Update
After the genius answer by #GarethD, I got this exception
You can use UNPIVOT to turn the columns into rows:
INSERT Palm_Farm (FarmID, PalmID, PalmTypeName, [Count])
SELECT upvt.FarmID,
p.PalmID,
p.PalmTypeName,
upvt.[Count]
FROM Farm AS f
UNPIVOT
( [Count]
FOR PalmTypeName IN ([Kenizy], [BarBedo], [BarBodo], [MorKodo])
) AS upvt
INNER JOIN Palms AS p
ON p.PalmTypeName = upvt.PalmTypeName;
Example on SQL Fiddle
The docs for UNPIVOT state:
UNPIVOT performs almost the reverse operation of PIVOT, by rotating columns into rows. Suppose the table produced in the previous example is stored in the database as pvt, and you want to rotate the column identifiers Emp1, Emp2, Emp3, Emp4, and Emp5 into row values that correspond to a particular vendor. This means that you must identify two additional columns. The column that will contain the column values that you are rotating (Emp1, Emp2,...) will be called Employee, and the column that will hold the values that currently reside under the columns being rotated will be called Orders. These columns correspond to the pivot_column and value_column, respectively, in the Transact-SQL definition.
To explain further how unpivot works, I will look at the first row original table:
FarmID | Kenizy | BarBedo | BarBodo | MorKodo
-----------------------------------------------
3 | 20 | 12 | 45 | 60
So what UPIVOT will do is look for columns specified in the UNPIVOT statement, and create a row for each column:
SELECT upvt.FarmID, upvt.PalmTypeName, upvt.[Count]
FROM Farm AS f
UNPIVOT
( [Count]
FOR PalmTypeName IN ([Kenizy], [BarBedo])
) AS upvt;
So here you are saying, for every row find the columns [Kenizy] and [BarBedo] and create a row for each, then for each of these rows create a new column called PalmTypeName that will contain the column name used, then put the value of that column into a new column called [Count]. Giving a result of:
FarmID | Kenizy | Count |
---------------------------
3 | Kenizy | 20 |
3 | BarBedo | 12 |
If you are running SQL Server 2000, or a later version with a lower compatibility level, then you may need to use a different query:
INSERT Palm_Farm (FarmID, PalmID, PalmTypeName, [Count])
SELECT f.FarmID,
p.PalmID,
p.PalmTypeName,
[Count] = CASE upvt.PalmTypeName
WHEN 'Kenizy' THEN f.Kenizy
WHEN 'BarBedo' THEN f.BarBedo
WHEN 'BarBodo' THEN f.BarBodo
WHEN 'MorKodo' THEN f.MorKodo
END
FROM Farm AS f
CROSS JOIN
( SELECT PalmTypeName = 'Kenizy' UNION ALL
SELECT PalmTypeName = 'BarBedo' UNION ALL
SELECT PalmTypeName = 'BarBodo' UNION ALL
SELECT PalmTypeName = 'MorKodo'
) AS upvt
INNER JOIN Palms AS p
ON p.PalmTypeName = upvt.PalmTypeName;
This is similar, but you have to create the additional rows yourself using UNION ALL inside the subquery upvt, then choose the value for [Count] using a case expression.
To update when the row exists you can use MERGE
WITH Data AS
( SELECT upvt.FarmID,
p.PalmID,
p.PalmTypeName,
upvt.[Count]
FROM Farm AS f
UNPIVOT
( [Count]
FOR PalmTypeName IN ([Kenizy], [BarBedo], [BarBodo], [MorKodo])
) AS upvt
INNER JOIN Palms AS p
ON p.PalmTypeName = upvt.PalmTypeName
)
MERGE Palm_Farm WITH (HOLDLOCK) AS pf
USING Data AS d
ON d.FarmID = pf.FarmID
AND d.PalmID = pf.PalmID
WHEN NOT MATCHED BY TARGET THEN
INSERT (FarmID, PalmID, PalmTypeName, [Count])
VALUES (d.FarmID, d.PalmID, d.PalmTypeName, d.[Count])
WHEN MATCHED THEN
UPDATE
SET [Count] = d.[Count],
PalmTypeName = d.PalmTypeName;