Is it possible to join a table whereby the table name is a value in a column?
Here is a TABLE called food:
id food_name price_table pricing_reference_id
1 | 'apple' | 'daily_price' | 13
2 | 'banana' | 'monthly_price' | 13
3 | 'hotdog' | 'weekly_price' | 17
4 | 'sandwich' | 'monthly_price' | 9
There are three other tables (pricing tables): daily_price, weekly_price, and monthly_price tables.
Side note: Despite their names, the three pricing tables display vastly different kinds of information, which is why the three tables were not merged into one table
Each row in the food table can only be joined with one of the three pricing tables at most.
The following does not work -- it is just to illustrate what I am trying to get at:
SELECT *
FROM food
LEFT JOIN food.price_table ON food.pricing_reference_id = daily_price.id
WHERE id = 1;
Obviously the query does not work. Is there any way that the name of the table in the price_table column could be used as the table name in a join?
I would suggest left joins:
select f.*,
coalesce(dp.price, wp.price, mp.price) as price
from food f left join
daily_price dp
on f.pricing_reference_id = dp.id and
f.pricing_table = 'daily_price' left join
weekly_price wp
on f.pricing_reference_id = wp.id and
f.pricing_table = 'weekly_price' left join
monthly_price mp
on f.pricing_reference_id = mp.id and
f.pricing_table = 'monthly_price' ;
For the columns you reference, you need to use coalesce() to combine the results from the three tables. You say that the tables have different data, so you would need to list the columns separately.
The main reason I recommend this approach is performance. I think the left joins should be faster than any solution that uses union all.
Could you get your expected result using by a derived table with UNION SELECT which has a column of each table name?
SELECT *
FROM food
LEFT JOIN
(
SELECT 'daily_price' AS price_table, * FROM daily_price
UNION ALL SELECT 'monthly_price', * FROM monthly_price
UNION ALL SELECT 'weekly_price', * FROM weekly_price
) t
ON food.price_table = t.price_table AND
food.pricing_reference_id = t.id
ORDER BY food.id;
dbfiddle
Related
Context:
I have two tables: ks__dokument and ks_pz. It's one-to-many relation where records from ks__dokument may have multiple records assigned from ks_pz.
Goal:
I want to show every row from ks__dokument and every row from ks__dokument must be shown only once.
What I tried:
Here is query I tried:
SELECT DISTINCT ks_id, * FROM ks__dokument AS dok1
LEFT JOIN ks_pz ON ks_id = kp_ksid
But it still shows duplicates.
EDITS
That ORDER BY and WHERE was unnecessary.
I dont need DISTINCT, it's just what I tried.
STRUCTURE OF TABLES
ks__dokument structure:
| ks_id | X | X | X | X | X | X |
ks_pz:
| kp_id | kp_ksid | X | X | X |
'X' are unimportant columns. kp_ksid is foreign key for ks__dokument.
Use OUTER APPLY:
SELECT dok1.*, k2.*
FROM ks__dokument dok1 OUTER APPLY
(SELECT TOP (1) *
FROM ks_pz
WHERE ks_id = kp_ksid
) k2
WHERE ks_usuniety = 0 AND
ks_data_otrzymania >= '2020-08-31'
ORDER BY ks_rok, ks_nr ASC;
Normally, there would be an ORDER BY in the subquery to specify which row to return.
The structure of your question makes it impossible to know if the ORDER BY should be in the subquery or in the outer query -- and the same for the WHERE conditions.
You really need to specify the tables where columns are coming from.
You can try the below - move your WHERE condition clause to ON clause
SELECT DISTINCT ks_id, * FROM ks__dokument AS dok1
LEFT JOIN ks_pz ON ks_id = kp_ksid
and ks_usuniety = 0 AND ks_data_otrzymania >= '2020-08-31'
ORDER BY ks_rok, ks_nr ASC
I want to join the 2 tables to the first table and group by a vendor name. I have three tables listed below.
Vendors Table
| id | name
|:-----------|------------:|
| test-id | Vendor Name |
VendorOrders Table
| id | VendorId | Details | isActive(Boolean)| price |
|:-----------|------------:|:------------:| -----------------| --------
| random-id | test-id | Sample test | TRUE | 5000
OrdersIssues Table
| id | VendorOrderId| Details. |
|:-----------|--------------:-----------:|
| order-id | random-id | Sample test|
The expected output is to count how many orders belong to a vendor and how many issues belongs to a vendor order.
I have the below code but it's not giving the right output.
SELECT "vendors"."name" as "vendorName",
COUNT("vendorOrders".id) as allOrders,
COUNT("orderIssues".id) as allIssues
FROM "vendors"
LEFT OUTER JOIN "vendorOrders" ON "vendors".id = "vendorOrders"."vendorId"
LEFT OUTER JOIN "orderIssues" ON "orderIssues"."vendorOrderId" = "vendorOrders"."id"
GROUP BY "vendors".id;```
You need the keyword DISTINCT, at least for allOrders:
SELECT v.name vendorName,
COUNT(DISTINCT vo.id) allOrders,
COUNT(DISTINCT oi.id) allIssues
FROM vendors v
LEFT OUTER JOIN vendorOrders vo ON v.id = vo.vendorId
LEFT OUTER JOIN orderIssues oi ON oi.vendorOrderId = vo.id
GROUP BY v.id, v.name;
Consider using aliases instead of full table names to make the code shorter and more readable.
You are joining along two related dimensions. The overall number of rows is the number of issues. But to get the number of orders, you need a distinct count:
SELECT v.*, count(distinct vo.id) as num_orders,
COUNT(oi.vendororderid) as num_issues
FROM vendors v LEFT JOIN
vendorOrders vo
ON v.id = vo.vendorId LEFT JOIN
orderIssues oi
ON oi.vendorOrderId = vo.id
GROUP BY v.id;
Notes:
Table aliases make the query easier to write and to read.
Quoting column and table names makes the query harder to write and read. Don't quote identifiers (you may need to recreate the tables).
Postgres support SELECT v.* . . . GROUP BY v.id assuming that the id is the primary key (actually, it only needs to be unique). This seems like a reasonable assumption.
I have the following tables:
TABLE PLAYER
id | name
1 | A
2 | B
3 | C
4 | D
TABLE PAIRINGS
id | player_a | player_b
1 | 3 |1
2 | 2 |4
Both columns in table Pairings are foreign keys to column id of table player.
My problem is, I would like to avoid making a query from code every time I want to know which is my player's name (like, Select name From Player Where Id = pairings.player_a). I have thought about adding Name as an extra columnd to Pairings table, but that would denormalize it.
Instead, it would be nice if I could get the names in just one query, like:
RESULT
player_a | player_b
C | A
B | D
Is it this possible? Thanks so much in advance.
You may join the PAIRINGS table to the PLAYER table, twice:
SELECT
p1.name AS player_a,
p2.name AS player_b
FROM PAIRINGS pr
INNER JOIN PLAYER p1
ON pr.player_a = p1.id
INNER JOIN PLAYER p2
ON pr.player_b = p2.id;
Demo
Don't do it! One of the points of using a relational database is that data is stored in only one place. That is a big convenience. Of course, there are exceptions, but these exceptions should have firm reasons.
In this case, just define a view:
CREATE VIEW vw_pairings AS
SELECT p.*, pa.name AS player_a_name,
pb.name AS player_b_name
FROM PAIRINGS p JOIN
PLAYER pa
ON p.player_a = pa.id JOIN
PLAYER pb
ON p.player_b = pb.id;
When you query from the view, you will see the names, along with all the other information in the PAIRINGS table.
Hope can help you
Select * Into #PLAYER From (
Select 1 [ID], 'A' [Name] Union All
Select 2 [ID], 'B' [Name] Union All
Select 3 [ID], 'C' [Name] Union All
Select 4 [ID], 'D' [Name]
) A
Select * Into #PAIRINGS From (
Select 1 [ID], 3 [PLAYER_A], 1 [PLAYER_B] Union All
Select 2 [ID], 2 [PLAYER_A], 4 [PLAYER_B]
) A
Select
P.ID, A.NAME, B.NAME
From #PAIRINGS P
Left Join #PLAYER A On A.ID = P.PLAYER_A
Left Join #PLAYER B On B.ID = P.PLAYER_B
You can create view, for avoid making query
Example
Create View vwPAIRINGS As
Select
P.ID, A.NAME, B.NAME
From #PAIRINGS P
Left Join #PLAYER A On A.ID = P.PLAYER_A
Left Join #PLAYER B On B.ID = P.PLAYER_B
After that, just select usual
Select * from vwPAIRINGS
Let's say :
SELECT Item.Id, Item.ParentId FROM Item ..."
Returns me this data:
Id | ParentId
----------------
1 | NULL
2 | 17
3 | 13
Is there is a way to get this data as one column by using some kind of UNION but on columns from only one SELECT ? Something like:
SELECT (Item.Id UNION Item.ParentId) AS Id FROM Item...
Result :
Id |
----
1 |
2 |
3 |
NULL
17 |
13 |
EDIT EXAMPLE:
I have Media Table:
Id | ParentId
----------------
1 | NULL
2 | 1
3 | 2
It have relations with itself, this is some kind of 3 level tree structure
(Series -> Seasons -> Episodes)
There is another Table Offer which contain information about availability:
Id | MediaId | Availability
------------------------------
1 | 3 | true
I need to get id's of all media that are available, but also all parent's id, of all levels.
I was thinking about:
SELECT Media.Id, MediaSeason.Id, MediaSeries.Id FROM Media
LEFT JOIN Media AS MediaSeason ON MediaSeason.Id = Media.ParentId
LEFT JOIN Media AS MediaSeries ON MediaSeries.Id = MediaSeason.ParentId
LEFT JOIN Offer ON Offer.MediaId = Media.Id
WHERE Offer.Availability = true
This gives me all id's i need but in three different columns and I'm trying to find a way to put it into one, without repeating join and where login in 3 different SELECTS.
I'm using MSSQL.
Try this:
SELECT * FROM (SELECT Item.Id FROM Item ...
UNION ALL
SELECT Item.ParentId FROM Item ...)
If your children and parents are in the same table (Item)
SELECT Id FROM Item
Will retrieve all Items, including Parents because parents are also Items.
But if what you want is to not repeat the where clause and have Ids of any matched Media and its associated parents (even if the parent media does not match the where clause) you can try this:
SELECT
m.Id
FROM
Media m INNER JOIN (
SELECT
m2.Id, m2.ParentId
FROM
Media m2
LEFT JOIN Offer ON Offer.MediaId = m2.Id
WHERE
Offer.Availability = true
) tmp ON (tmp.Id = m.Id OR tmp.ParentId = m.Id)
Finally, for three levels:
SELECT
m.Id
FROM
Media m INNER JOIN (
SELECT
m2.Id, m2.ParentId, m3.ParentId AS GrandParentId
FROM
Media m2
LEFT JOIN Media m3 ON m2.ParentId = m3.Id
LEFT JOIN Offer ON Offer.MediaId = m2.Id
WHERE
Offer.Availability = true
) tmp ON (tmp.Id = m.Id OR tmp.ParentId = m.Id OR tmp.GrandParentId = m.Id)
SELECT DISTINCT
pivot_hierarchy.media_id
FROM
offers o
LEFT JOIN
media m1
ON m1.id = o.media_id
LEFT JOIN
media m2
ON m2.id = m1.parent_id
OUTER APPLY
(
SELECT o.media_id
UNION ALL
SELECT m1.parent_id WHERE m1.parent_id IS NOT NULL
UNION ALL
SELECT m2.parent_id WHERE m2.parent_id IS NOT NULL
)
AS pivot_hierarchy
WHERE
o.availability = 'true'
Everything up to the APPLY should be self explanatory. Get the offers, get the parent of that media if it has one, and the parent of that media if it has one.
The APPLY then joins each row on to a function that can return more than one row each. In this case the function returns 1, 2 or 3 rows. Those being the media id, it parent if it has one, and its grand-parent if it has one. To do that, the function unions the three input columns, provided that they’re not null.
This avoids having to join back on to the media table again.
Also, you need a distinct in the select. Otherwise the same series or season id could return multiple times.
Nested selects can be avoided in UNION
create table tab (
Id int,
ParentId int
);
insert into tab
values
(1, NULL),
(2, 17),
(3, 13);
then do
select ID as ID
from tab
union all
select ParentId as ID
from tab
NOTE: DB queries can be conveniently tested live, e.g. http://sqlfiddle.com/#!17/7a3a8/2
I am using postgresql.
I have a table called custom_field_answers. The data looks like this
Id | product_id | value | number_value |
4 | 2 | | 117 |
3 | 1 | | 107 |
2 | 1 | bangle | |
1 | 2 | necklace | |
I want to find all the products which has text_value as 'bangle' and number_value less than 50.
Here was my first attempt.
SELECT "products".* FROM "products" INNER JOIN "custom_field_answers"
ON "custom_field_answers"."product_id" = "products"."id"
WHERE ("custom_field_answers"."value" ILIKE 'bangle')
Here is my second attempt.
SELECT "products".* FROM "products" INNER JOIN "custom_field_answers"
ON "custom_field_answers"."product_id" = "products"."id"
where ("custom_field_answers"."number_value" < 50)
Here is my final attempt.
SELECT "products".* FROM "products" INNER JOIN "custom_field_answers"
ON "custom_field_answers"."product_id" = "products"."id"
WHERE ("custom_field_answers"."value" ILIKE 'bangle')
AND ("custom_field_answers"."number_value" < 50)
but this does not select any product record.
A WHERE clause can only look at columns from one row at a time.
So if you need a condition that applies to two different rows from a table, you need to join to that table twice, so you can get columns from both rows.
SELECT p.*
FROM "products" AS p
INNER JOIN "custom_field_answers" AS a1 ON p."id" = a1."product_id"
INNER JOIN "custom_field_answers" AS a2 ON p."id" = a1."product_id"
WHERE a1."value" = 'bangle' AND a2."number_value" < 50
It produces no records because there is no custom_field_answers record that meets both criteria. What you want is a list of product_ids that have the necessary records in the table. Just in case no one gets to writing the SQL for you, and until I have a chance to work it out myself, I thought I would at least explain to you why your query is not working.
This should work:
SELECT p.* FROM products LEFT JOIN custom_field_answers c
ON (c.product_id = p.id AND c.value LIKE '%bangle%' AND c.number_value
Hope it helps
Your bangle-related number_value fields are null, so you won't be able to do a straight comparison in those cases. Instead, convert your nulls to 0s first.
SELECT "products".* FROM "products" INNER JOIN "custom_field_answers"
ON "custom_field_answers"."product_id" = "products"."id"
WHERE ("custom_field_answers"."value" LIKE '%bangle%')
AND (coalesce("custom_field_answers"."number_value", 0) < 50)
Didn't actually test it, but this general idea should work:
SELECT *
FROM products
WHERE
EXISTS (
SELECT *
FROM custom_field_answers
WHERE
custom_field_answers.product_id = products.id
AND value = 'bangle'
)
AND EXISTS (
SELECT *
FROM custom_field_answers
WHERE
custom_field_answers.product_id = products.id
AND number_value < 5
)
In plain English: Get all products such that...
there is a related row in custom_field_answers where value = 'bangle'
and there is (possibly different) related row in custom_field_answers where number_value < 5.