I want to join 3 tables (as presented below), but I can't figure out how to do it:
Table 1
vendor_id
---------
1
2
3
4
Table 2
cuisine_type | vendor_id
------------------------
a |1
b |1
c |1
Table 3
cuisine_type|cuisine
--------------------
a |pizza
b |rice
c |steak
I would like to join the 3 tables and get this:
vendor_id|cuisine_type|cuisine
------------------------------
1 |a, b, c |pizza, steak, rice
2.......
I hope this makes sense. I'm very new to postgreSQL so maybe I'm missing something very easy/obvious.
This is a simple join and an aggregation based on the vendor_id:
select v.vendor_id,
string_agg(ct.cuisine_type, ', ') as cuisine_type,
string_agg(c.cuisine, ', ') as cuisine
from table_1 as v
join table_2 as ct on v.vendor_id = ct.vendor_id
join table_3 as c on ct.cuisine_type = c.cuisine_type
group by v.vendor_id;
Your table structure looks a bit strange. For instance, why does each cuisine type have only a single cuisine? Normally, I would expect the vendor to be connected to the cuisines, and then each cuisine to have a type.
However, that is not this question. With the data you have provided, you can use string_agg():
select v.vendor_id, string_agg(cuisine_type, ', ') as cuisine_types,
string_agg(cuisine, ', ') as cuisines
from table1 v left join
table2 v2c
on v.vendor_id = v2c.vendor_id left join
table3 c
on c.cuisine_type = v2c.cuisine_type
group by v.vendor_id;
Related
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
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
I'll start with a simplified example of my table:
+-----+----------+
|Name |Teaches |
+-----+----------+
|Dave |Science |
+-----+----------+
|Dave |History |
+-----+----------+
|Alice|History |
+-----+----------+
|Alice|Literature|
+-----+----------+
|Alice|Science |
+-----+----------+
|John |History |
+-----+----------+
I'm trying to select those people who also teach the same classes as Dave. (In this case, Alice). I'm thinking of using a cursor to go through Dave's courses and selecting those people who teach the same course and intersecting the results, but I'd like to know if there is a better (simpler) way.
Here is one method:
select t.name
from t join
t td
on td.teaches = t.teaches
where td.name = 'Dave'
group by t.name
having count(*) = (select count(*) from t where t.name = 'Dave');
You need to use Self join, something like this
SELECT a.NAME
FROM Table1 a
INNER JOIN (SELECT Teaches,
Count(*)OVER() AS cnt
FROM Table1
WHERE NAME = 'Dave') b
ON a.Teaches = b.Teaches
WHERE a.NAME <> 'Dave'
GROUP BY a.NAME,
b.cnt
HAVING Count(*) = b.cnt
One method, used CTE here.
;WITH CTE_Parent
AS (
SELECT Name,Teaches,COUNT(*) OVER() AS Parent_Count
FROM #Teachers
WHERE Name = 'Dave'
)
SELECT T.Name
FROM #Teachers AS T
INNER JOIN CTE_Parent AS C ON C.Name <> T.Name
AND C.Teaches= T.Teaches
GROUP BY T.Name,C.Parent_Count
HAVING COUNT(*) = C.Parent_Count
I have a problem here and I got a bit confused with outer/inner joins and multiple conditions
We have 4 tables with - columns:
table_cars - id | brand | type | license
table_equipments - id | name | description
table_distances - id_car | date | distance
table_cars_equipments - id_car | id_equipment
First query should show all cars that have equipment "fire extinguisher" and have been driving yesterday.
I have tried to write this query:
SELECT table_cars_equipments.id_car
FROM table_equipments
INNER JOIN table_cars_equipments
ON table_equipments.id = table_cars_equipments.id_equipment
AND table_equipments.name LIKE 'fire extinguisher';
Though I am still confused how to add the cars which had been driving yesterday, I don't know how to make the connection with the table table_distances.
Add another JOIN with the table table_cars and another one to the table table_distances. Then add a condition to the WHERE clause to get only those cars that have been driving yesterday. Something like this:
SELECT
c.id,
c.brand,
c.type,
c.license
ce.id_car,
...
from table_equipments AS e
INNER JOIN table_cars_equipments AS ce ON e.id = ec.id_equipment
INNER JOIN table_cars AS c ON c.id = ce.id_car
INNER JOIN table_distances AS d ON d.id_car = c.id
WHERE e.name LIKE 'fire extinguisher'
AND d.date = ?;
Note that: I used aliases for the table c, e etc, instead of the tables' full names.
I am trying to get a single result (PHONE) per match (CONTACT_ID) in a Left Outer Join. I imagine that there is a way to accomplish this with the preference (or order) being set by another column/field- the phone type (TYPE), but I haven't been able to figure it out. Below is a list of facts to help better explain what I am trying to accomplish and then following is an example Table A and B with the desired result. I've looked at min() and group by, but I don't know how to make those work here. As a side note, after this is working, I will be joining it to more tables to the left of it in a simpler fashion.
The student can have an unlimited number of CONTACT_ID.
A contact does not always have all phone types.
The preferred order of phone types (TYPE) is C,H,W (which, fortunately, happens to be alphabetical)
ignore match and go to the next in priority if PHONE is null
TableA:
STUDENT_ID CONTACT_ID
---------- ----------
X 1
X 2
Y 3
Y 4
TableB:
CONTACT_ID TYPE PHONE
---------- ---- -----
1 H 21
1 C
1 W 44
2 H 78
2 C 92
2 W 11
Desired Result:
STUDENT_ID CONTACT_ID TYPE PHONE
---------- ---------- ---- -----
X 1 H 21
X 2 C 92
Y 3
Y 4
Here is the query that I have that will make a join with all phone matches (minus all of my crazy attempts at getting what I want).
SELECT *
FROM Table TableA T1
LEFT OUTER JOIN TableB T2 ON T1.CONTACT_ID = T2.CONTACT_ID
All help greatly appreciated!
Edited code from Stefan Onofrei's solution:
(results in some duplicate entries)
SELECT
T1.STUDENT_ID,
T1.CONTACT_ID,
T2.PHONE_TYPE,
T3.PHONE
FROM REG_STU_CONTACT T1
INNER JOIN
(SELECT MIN(PHONE_TYPE) AS PHONE_TYPE, CONTACT_ID
FROM REG_CONTACT_PHONE
WHERE PHONE IS NOT NULL
GROUP BY CONTACT_ID) T2 ON T1.CONTACT_ID = T2.CONTACT_ID
INNER JOIN REG_CONTACT_PHONE T3 ON T2.CONTACT_ID = T3.CONTACT_ID AND T2.PHONE_TYPE = T3.PHONE_TYPE
ORDER BY T1.STUDENT_ID
Select A.STUDENT_ID A.CONTACT_ID B.TYPE c.PHONE
from TableA A
inner join
(select MIN(type ) as type, Contact_ID
from Tableb
where phone is not null
group by contactid) B
on A.contactid = b.contactid
inner join Tableb C
on B.contactid = c.conatctid and b.type = c.type