If i have two tables entry and entry_metadata, with the entry_metadata as a description table for the entry referenced by entry_id and a variable.
If i have this :
entry
id | name |
-------------
1 | entry1 |
2 | entry2 |
3 | entry3 |
entry_metadata
id | entry_id | variable | value
1 | 1 | width | 10
2 | 1 | height | 5
3 | 2 | width | 8
4 | 2 | height | 7
5 | ... | .... | ..
and i'm getting the table :
id | name | width | height| ... | ...
-----------------------------------------
1 | entry1 | 10 | 5 |
2 | entry2 | 8 | 7 |
3 | entry3 | .. | .. |
by the sql :
select e.name, em.width, emr.height
from
public.entry e
left join
public.entry_metadata em
on
em.entry_id = e.id and em.variable = 'width'
left join
public.entry_metadata emr
on
emr.entry_id = e.id and emr.variable = 'height'
The query above works. But as I add more variables to get the values (the entry_metadata table includes a large variety of variables) from the entry metadata. The query gets really really slow. every join I do slows down the execution greatly. Is there a way to get around this?
You can also do this with conditional aggregation:
select id, name,
max(case when variable = 'width' then value end) as width,
max(case when variable = 'height' then value end) as height
from public.entry_metadata em
group by id, name;
Adding additional columns is just adding more aggregation functions.
Just use subselects for this:
SELECT
e.id,
e.name,
(SELECT em.value FROM public.entry_metadata em WHERE em.entry_id = e.id AND em.variable = 'width') AS width,
(SELECT em.value FROM public.entry_metadata em WHERE em.entry_id = e.id AND em.variable = 'height') AS height
FROM
public.entry e
So for each new variable you just need to add one more subselect.
Is there a way to get around this?
Yes, replace entry_metadata table with addtional column in entry (possible solutions are hstore or jsonb) with key - value storage of entry metadata.
Btw. your tables represents well known controversial database desing pattern known as "Entity Attribute Value".
Related
I have a Family table:
SELECT * FROM Family;
id | Surname | Oldest | Oldest_Age
---+----------+--------+-------
1 | Byre | NULL | NULL
2 | Summers | NULL | NULL
3 | White | NULL | NULL
4 | Anders | NULL | NULL
The Family.Oldest column is not yet populated. There is another table of Children:
SELECT * FROM Children;
id | Name | Age | Family_FK
---+----------+------+--------
1 | Jake | 8 | 1
2 | Martin | 7 | 2
3 | Sarah | 10 | 1
4 | Tracy | 12 | 3
where many children (or no children) can be associated with one family. I would like to populate the Oldest column using an UPDATE ... SET ... statement that sets it to the Name and Oldest_Age of the oldest child in each family. Finding the name of each oldest child is a problem that is solved quite well here: How can I SELECT rows with MAX(Column value), DISTINCT by another column in SQL?
However, I don't know how to use the result of this in an UPDATE statement to update the column of an associated table using the h2 database.
The following is ANSI-SQL syntax that solves this problem:
update family
set oldest = (select name
from children c
where c.family_fk = f.id
order by age desc
fetch first 1 row only
)
In h2, I think you would use limit 1 instead of fetch first 1 row only.
EDIT:
For two columns -- alas -- the solution is two subqueries:
update family
set oldest = (select name
from children c
where c.family_fk = f.id
order by age desc
limit 1
),
oldest_age = (select age
from children c
where c.family_fk = f.id
order by age desc
limit 1
);
Some databases (such as SQL Server, Postgres, and Oracle) support lateral joins that can help with this. Also, row_number() can also help solve this problem. Unfortunately, H2 doesn't support this functionality.
In MS Access was very easy to acomplish but I'm having troubles with SQL Server
I have this query:
SELECT Organigrama.Item, Organigrama.Id, Organigrama.ParentItem, Rol_Menu.Cod_Rol
FROM Rol_Menu RIGHT JOIN
Organigrama ON Rol_Menu.Cod_Menu = Organigrama.Id
WHERE (Rol_Menu.Cod_Rol = '5')
The purpose is to get all the items of Organigrama and the elements in common with Rol_Menu.Col_Rol appears with 5, the others with Null
I need to fill a menu structure into a treeview
When the user select another Rol just get nodes checked that rol have access to
im determining if in the row the Col_Rol isn't null so the query I need to get
something like this:
Item | Id | ParentItem | Cod_Rol
A | 3 | null | 5
B | 4 | A | 5
C | 5 | A | null
D | 6 | B | 5
E | 7 | C | null
F | 8 | E | null
I think you just need to include the extra restriction in the join criteria rather then the where clause. The criteria are evaluated before the outer join adds the null columns. The where clause is evaluated afterwards, and eliminates the nulls.
select
Organigrama.Item,
Organigrama.Id,
Organigrama.ParentItem,
Rol_Menu.Cod_Rol
from
Rol_Menu
right join
Organigrama
on Rol_Menu.Cod_Menu = Organigrama.Id and
Rol_Menu.Cod_Rol = '5'
either that or add or Rol_Menu.Cod_Rol is null to the end of the where clause.
Say, I have an organizational structure that is 5 levels deep:
CEO -> DeptHead -> Supervisor -> Foreman -> Worker
The hierarchy is stored in a table Position like this:
PositionId | PositionCode | ManagerId
1 | CEO | NULL
2 | DEPT01 | 1
3 | DEPT02 | 1
4 | SPRV01 | 2
5 | SPRV02 | 2
6 | SPRV03 | 3
7 | SPRV04 | 3
... | ... | ...
PositionId is uniqueidentifier. ManagerId is the ID of employee's manager, referring PositionId from the same table.
I need a SQL query to get the hierarchy tree going down from a position, provided as parameter, including the position itself. I managed to develop this:
-- Select the original position itself
SELECT
'Rank' = 0,
Position.PositionCode
FROM Position
WHERE Position.PositionCode = 'CEO' -- Parameter
-- Select the subordinates
UNION
SELECT DISTINCT
'Rank' =
CASE WHEN Pos2.PositionCode IS NULL THEN 0 ELSE 1+
CASE WHEN Pos3.PositionCode IS NULL THEN 0 ELSE 1+
CASE WHEN Pos4.PositionCode IS NULL THEN 0 ELSE 1+
CASE WHEN Pos5.PositionCode IS NULL THEN 0 ELSE 1
END
END
END
END,
'PositionCode' = RTRIM(ISNULL(Pos5.PositionCode, ISNULL(Pos4.PositionCode, ISNULL(Pos3.PositionCode, Pos2.PositionCode)))),
FROM Position Pos1
LEFT JOIN Position Pos2
ON Pos1.PositionId = Pos2.ManagerId
LEFT JOIN Position Pos3
ON Pos2.PositionId = Pos3.ManagerId
LEFT JOIN Position Pos4
ON Pos3.PositionId = Pos4.ManagerId
LEFT JOIN Position Pos5
ON Pos4.PositionId = Pos5.ManagerId
WHERE Pos1.PositionCode = 'CEO' -- Parameter
ORDER BY Rank ASC
It works not only for 'CEO' but for any position, displaying its subordinates. Which gives me the following output:
Rank | PositionCode
0 | CEO
... | ...
2 | SPRV55
2 | SPRV68
... | ...
3 | FRMN10
3 | FRMN12
... | ...
4 | WRKR01
4 | WRKR02
4 | WRKR03
4 | WRKR04
My problems are:
The output does not include intermediate nodes - it will only output end nodes, i.e. workers and intermediate managers which have no subordinates. I need all intermediate managers as well.
I have to manually UNION the row with original position on top of the output. I there any more elegant way to do this?
I want the output to be sorted in hieararchical tree order. Not all DeptHeads, then all Supervisors, then all Foremen then all workers, but like this:
Rank | PositionCode
0 | CEO
1 | DEPT01
2 | SPRV01
3 | FRMN01
4 | WRKR01
4 | WRKR02
... | ...
3 | FRMN02
4 | WRKR03
4 | WRKR04
... | ...
Any help would be greatly appreciated.
Try a recursive CTE, the example on TechNet is almost identical to your problem I believe:
http://technet.microsoft.com/en-us/library/ms186243(v=sql.105).aspx
Thx, everyone suggesting CTE. I got the following code and it's working okay:
WITH HierarchyTree (PositionId, PositionCode, Rank)
AS
(
-- Anchor member definition
SELECT PositionId, PositionCode,
0 AS Rank
FROM Position AS e
WHERE PositionCode = 'CEO'
UNION ALL
-- Recursive member definition
SELECT e.PositionId, e.PositionCode,
Rank + 1
FROM Position AS e
INNER JOIN HierarchyTree AS d
ON e.ManagerId = d.PositionId
)
SELECT Rank, PositionCode
FROM HierarchyTree
GO
I had a similar problem to yours on a recent project but with a variable recursion length - typically between 1 and 10 levels.
I wanted to simplify the SQL side of things so I put some extra work into the logic of storing the recursive elements by storing a "hierarchical path" in addition to the direct manager Id.
So a very contrived example:
Employee
Id | JobDescription | Hierarchy | ManagerId
1 | DIRECTOR | 1\ | NULL
2 | MANAGER 1 | 1\2\ | 1
3 | MANAGER 2 | 1\3\ | 1
4 | SUPERVISOR 1 | 1\2\4 | 2
5 | SUPERVISOR 2 | 1\3\5 | 3
6 | EMPLOYEE 1 | 1\2\4\6 | 4
7 | EMPLOYEE 2 | 1\3\5\7 | 5
This means you have the power to very quickly query any level of the tree and get all descendants by using a LIKE query on the Hierarchy column
For example
SELECT * FROM dbo.Employee WHERE Hierarchy LIKE '\1\2\%'
would return
MANAGER 1
SUPERVISOR 1
EMPLOYEE 1
Additionally you can also easily get one level of the tree by using the ManagerId column.
The downside to this approach is you have to construct the hierarchy when inserting or updating records but believe me when I say this storage structure saved me a lot of pain later on without the need for unnecessary query complexity.
One thing to note is that my approach gives you the raw data - I then parse the result set into a recursive strongly typed structure in my services layer. As a rule I don't tend to format output in SQL.
I am representing itemsets in SQL (SQLite, if relevant). My tables look like this:
ITEMS table:
| ItemId | Name |
| 1 | Ginseng |
| 2 | Honey |
| 3 | Garlic |
ITEMSETS:
| ItemSetId | Name |
| ... | ... |
| 7 | GinsengHoney |
| 8 | HoneyGarlicGinseng |
| 9 | Garlic |
ITEMSETS2ITEMS
| ItemsetId | ItemId |
| ... | .... |
| 7 | 1 |
| 7 | 2 |
| 8 | 2 |
| 8 | 1 |
| 8 | 3 |
As you can see, an Itemset may contain several Items, and this relationship is detailed in the Itemset2Items table.
How can I check whether a new itemset is already in the table, and if so, find its ID?
For instance, I want to check whether "Ginseng, Garlic, Honey" is an existing itemset. The desired answer would be "Yes", because there exists a single ItemsetId which contains exactly these three IDs. Note that the set is unordered: a query for "Honey, Garlic, Ginseng" should behave identically.
How can I do this?
I would recommend that you start by placing the item sets that you want to check into a table, with one row per item.
The question is now about the overlap of this "proposed" item set to other itemsets. The following query provides the answer:
select itemsetid,
from (select coalesce(ps.itemid, is2i.itemid) as itemid, is2i.itemsetid,
max(case when ps.itemid is not null then 1 else 0 end) as inProposed,
max(case when is2i.itemid is not null then 1 else 0 end) as inItemset
from ProposedSet ps full outer join
ItemSets2items is2i
on ps.itemid = is2i.itemid
group by coalesce(ps.itemid, is2i.itemid), is2i.itemsetid
) t
group by itemsetid
having min(inProposed) = 1 and min(inItemSet) = 1
This joins all the proposed items with all the itemsets. It then groups by the items in each item set, giving a flag as to whether the item is in the set. Finally, it checks that all items in an item set are in both.
Sounds like you need to find an ItemSet that:
contains all the Items in your wanted list
doesn't contain any other Items
This example will return the ID of such an itemset if it exists.
Note: this solution is for MySQL, but it should work in SQLite once you change #variables into something SQLite understands, e.g. bind variables.
-- these are the IDs of the items in the new itemset
-- if you add/remove some, make sure to change the IN clauses below
set #id1 = 1;
set #id2 = 2;
-- this is the count of items listed above
set #cnt = 2;
SELECT S.ItemSetId FROM ItemSets S
INNER JOIN
(SELECT ItemsetId, COUNT(*) as C FROM ItemSets2Items
WHERE ItemId IN (#id1, #id2)
GROUP BY ItemsetId
HAVING COUNT(*) = #cnt
) I -- included ingredients
ON I.ItemsetId = S.ItemSetId
LEFT JOIN
(SELECT ItemsetId, COUNT(*) as C FROM ItemSets2Items
WHERE ItemId NOT IN (#id1, #id2)
GROUP BY ItemsetId
) A -- additional ingredients
ON A.ItemsetId = S.ItemSetId
WHERE A.C IS NULL
See fiddle for MySQL.
I have two tables as below in Accecss 2007.
Town Table
----------
TownName | FlatCount | DetachedCount | SemiCount
A | 5 | 3 | 4
B | 2 | 6 | 3
Cost Table
----------
Prop | PCost
Flat | 10
Detached | 20
Semi | 30
I would like to get an output like below by multiplying the Count from the Town table with the corresponding PCost in the Cost table. FlatCost = Town.FlatCount * Cost.PCost for a flat.
Results
-------
Town | FlatCount | FlatCost | DetachedCount | DetachedCost | .....
A | 5 | 50 | 3 | 60 |
B | 2 | 20 | 6 | 120 |
I have tried to do this by using IIF, but not sure how to get PCost for each property type within the IIF clause.
Thanks
Looks like you are mixing data and meta data e.g. the data value Flat in table Cost becomes metadata value (column name) FlatCount in table Town. This is not a good idea and is probably why you are having difficulties writing what should be a simply query.
Restructure your Town table so that it has columns TownName, Prop and PCount. And remember that most bad SQL DML is caused by bad SQL DDL ;)
You could use a subquery to retrieve the cost of an item:
select TownName
, FlatCount
, FlatCount * (select PCost from Cost where Prop = 'Flat') as FlatCost
, DetachedCount
, DetachedCount * (select PCost from Cost where Prop = 'Detached')
as DetachedCost
, ...
from Town
You have to cross join the tables. Then, for good values, put PCost in the multiplication, else, put 0.
You can then do a SUM using a Group by :
SELECT t.Town,
t.FlatCount,
SUM(t.FlatCount * IIF(c.Prop = 'Flat', c.PCost, 0)) AS FlatCost,
t.DetachedCount,
SUM(t.DetachedCount * IIF(c.Prop = 'Detached', c.PCost, 0)) AS DetachedCost,
FROM Town t, Cost c
GROUP BY t.Town, t.FlatCount, t.DetachedCount