Sorry if title isn't very descriptive. I have a table like this example, and am using sql server 2012:
PersonId | PetID
and want to join it to the following two tables
PersonId | PersonName | PersonAsset
AnimalId | AnimalName | Animal Asset
So the end result is:
PersonId | PetId | Name | Asset
-------------------------------
1 null Dave 1
null 1 Fido 2
The output you require can be achieved by using a LEFT JOIN for your two tables and ISNULL for the required fields.
For example (assuming the first table is named 'common'):
SELECT common.PersonId,
common.PetId,
ISNULL(person.PersonName, animal.AnimalName) AS Name,
ISNULL(person.PersonAsset, animal.AnimalAsset) AS Asset
FROM common
LEFT JOIN person ON common.PersonId = person.PersonId
LEFT JOIN animal ON common.AnimalId = animal.AnimalId
Related
Assume we have the following table whose purpose is to autogenerate a numeric id for distinct (name, location) tuples:
CREATE TABLE mapping
(
id bigserial PRIMARY KEY,
name text NOT NULL,
location text NOT NULL,
);
CREATE UNIQUE INDEX idx_name_loc on mapping(name location)
What is the most efficient way to query for a set of (name, location) tuples and autocreate any mappings that don't already exist, with all mappings (including the ones we created) being returned to the user.
My naive implementation would be something like:
SELECT id, name, location
FROM mappings
WHERE (name, location) IN ((name_1, location_1)...(name_n, location_n))
do something with the results in a programming language of may choice to work out which results are missing.
INSERT
INTO mappings (name, location)
VALUES (missing_name_1, missing_loc_1), ... (missing_name_2, missing_loc_2)
ON CONFLICT DO NOTHING
This gets the job done but I get the feeling there's probably something that can a) be done in pure sql and b) is more efficient.
You can use DISTINCT to get all possible values for the two columns, and CROSS JOIN to get their Carthesian product.
LEFT JOIN with the original table to get the actual records (if any):
CREATE TABLE mapping
( id bigserial PRIMARY KEY
, name text NOT NULL
, location text NOT NULL
, UNIQUE (name, location)
);
INSERT INTO mapping(name, location) VALUES ('Alice', 'kitchen'), ('Bob', 'bedroom' );
SELECT * FROM mapping;
SELECT n.name, l.location, m.id
FROM (SELECT DISTINCT name from mapping) n
CROSS JOIN (SELECT DISTINCT location from mapping) l
LEFT JOIN mapping m ON m.name = n.name AND m.location = l.location
;
Results:
DROP SCHEMA
CREATE SCHEMA
SET
CREATE TABLE
INSERT 0 2
id | name | location
----+-------+----------
1 | Alice | kitchen
2 | Bob | bedroom
(2 rows)
name | location | id
-------+----------+----
Alice | kitchen | 1
Alice | bedroom |
Bob | kitchen |
Bob | bedroom | 2
(4 rows)
And if you want to physically INSERT the missing combinations:
INSERT INTO mapping(name, location)
SELECT n.name, l.location
FROM (SELECT DISTINCT name from mapping) n
CROSS JOIN (SELECT DISTINCT location from mapping) l
WHERE NOT EXISTS(
SELECT *
FROM mapping m
WHERE m.name = n.name AND m.location = l.location
)
;
SELECT * FROM mapping;
INSERT 0 2
id | name | location
----+-------+----------
1 | Alice | kitchen
2 | Bob | bedroom
3 | Alice | bedroom
4 | Bob | kitchen
(4 rows)
I am new to the SQL world. I would like to replace the Games.home_team_id and Games.away_team_id with the Corresponding entry in the Teams.name column.
First I start by initializing a small table of data:
CREATE TABLE Games (id,away_team_id INT,away_team_score INT,home_team_id INT, home_team_score INT);
CREATE TABLE
INSERT INTO Games (id,away_team_id,away_team_score,home_team_id,home_team_score)
VALUES
(1,1,1,2,4),
(2,1,3,3,2),
(3,1,1,4,1),
(4,2,0,3,2),
(5,2,3,4,1),
(6,3,5,4,2)
;
INSERT 0 6
Then I create a template of a reference table
CREATE TABLE Teams (id INT, name VARCHAR(63);
CREATE TABLE
INSERT INTO Teams (id, name)
VALUES
(1, 'Oogabooga FC'),
(2, 'FC Milawnchair'),
(3, 'Ron\'s Footy United'),
(4, 'Pylon City FC')
;
INSERT 0 4
I would like to have the table displayed as such:
| id | away_team_name | away_team_score | home_team_name | home_team_score |
-----+----------------+-----------------+----------------+------------------
| 1 | Oogabooga FC | 1 | FC Milawnchair | 4 |
...
I managed to get a join query to show the first value from Teams.name in the away_team_name field using this JOIN:
SELECT
Games.id,
Teams.name AS away_team_name,
Games.away_team_score,
Teams.name AS home_team_name,
Games.home_team_score
FROM Games
JOIN Teams ON Teams.id = Games.away_team_id
;
| id | away_team_name | away_team_score | home_team_name | home_team_score |
-----+----------------+-----------------+----------------+------------------
| 1 | Oogabooga FC | 1 | Oogabooga FC | 4 |
...
But now I am stuck when I call it twice as a JOIN it shows the error:
SELECT
Games.id,
Teams.name AS away_team_name,
Games.away_team_score,
Teams.name AS home_team_name,
Games.home_team_score
FROM Games
JOIN Teams ON Teams.id = Games.away_team_id
JOIN Teams ON Teams.id = Games.home_team_id
;
ERROR: table name "teams" specified more than once
How do you reference the same reference the same column of the same table twice for a join?
You need to specify an alias for at least one of the instances of the table; preferably both.
SELECT
Games.id,
Away.name AS away_team_name,
Games.away_team_score,
Home.name AS home_team_name,
Games.home_team_score
FROM Games
JOIN Teams AS Away ON Away.id = Games.away_team_id
JOIN Teams AS Home ON Home.id = Games.home_team_id
Explanation: As you are joining to the same table twice, the DBMS (in your case, PostgreSQL) is unable to identify which of the tables you're referencing to when using its fields; the way to solve this is to assign an alias to the joined tables the same way you assign aliases for your columns. This way you can specify which of the joined instances are you referencing to in your SELECT, JOIN and WHERE statements.
So i have this task to resolve in Postgresql where for a given number of classIds that the user provides i have to return him the common properties of said classes.
I have three tables to represent the model (one class has multiple properties and one property can be in many classes)
Table classes:
---------------------------
| Id | Name | Description |
---------------------------
Table Properties:
---------------------------
| Id | Name | Description |
---------------------------
And finally table ClassProperties
------------------------
| ClassId | PropertyId |
------------------------
So the users gives me an array with classIds and i have to return him all common properties of all classes (like i said above)
As of now i'm only being able to return every property of all classes with this code:
select p.*
from properties as p
inner join ClassProperties as cp on cp.propertyid= p.id
where cp.classid = any ('{88d5fe8f-e19e-40b4-bc65-83ac64f825b0, a2a63bea-
aeee-4d3b-817e-cc635383c571}') ;
The ids as u can see are Guid, but that really does't matter. Any help would be appreciated. Thanks!
You can do this as:
select p.*
from properties p inner join
ClassProperties cp
on cp.propertyid = p.id
where cp.classid = any ('{88d5fe8f-e19e-40b4-bc65-83ac64f825b0, a2a63bea-aeee-4d3b-817e-cc635383c571}')
group by p.id
having count(*) = 2;
The count(*) should be count(distinct classid) if duplicates are allowed.
Note: the value "2" is the number of elements you are checking. You can also use array_length('{88d5fe8f-e19e-40b4-bc65-83ac64f825b0, a2a63bea-aeee-4d3b-817e-cc635383c571}').
Let's say I have this 3 tables
Countries ProvOrStates MajorCities
-----+------------- -----+----------- -----+-------------
Id | CountryName Id | CId | Name Id | POSId | Name
-----+------------- -----+----------- -----+-------------
1 | USA 1 | 1 | NY 1 | 1 | NYC
How do you get something like
---------------------------------------------
CountryName | ProvinceOrState | MajorCities
| (Count) | (Count)
---------------------------------------------
USA | 50 | 200
---------------------------------------------
Canada | 10 | 57
So far, the way I see it:
Run the first SELECT COUNT (GROUP BY Countries.Id) on Countries JOIN ProvOrStates,
store the result in a table variable,
Run the second SELECT COUNT (GROUP BY Countries.Id) on ProvOrStates JOIN MajorCities,
Update the table variable based on the Countries.Id
Join the table variable with Countries table ON Countries.Id = Id of the table variable.
Is there a possibility to run just one query instead of multiple intermediary queries? I don't know if it's even feasible as I've tried with no luck.
Thanks for helping
Use sub query or derived tables and views
Basically If You You Have 3 Tables
select * from [TableOne] as T1
join
(
select T2.Column, T3.Column
from [TableTwo] as T2
join [TableThree] as T3
on T2.CondtionColumn = T3.CondtionColumn
) AS DerivedTable
on T1.DepName = DerivedTable.DepName
And when you are 100% percent sure it's working you can create a view that contains your three tables join and call it when ever you want
PS: in case of any identical column names or when you get this message
"The column 'ColumnName' was specified multiple times for 'Table'. "
You can use alias to solve this problem
This answer comes from #lotzInSpace.
SELECT ct.[CountryName], COUNT(DISTINCT p.[Id]), COUNT(DISTINCT c.[Id])
FROM dbo.[Countries] ct
LEFT JOIN dbo.[Provinces] p
ON ct.[Id] = p.[CountryId]
LEFT JOIN dbo.[Cities] c
ON p.[Id] = c.[ProvinceId]
GROUP BY ct.[CountryName]
It's working. I'm using LEFT JOIN instead of INNER JOIN because, if a country doesn't have provinces, or a province doesn't have cities, then that country or province doesn't display.
Thanks again #lotzInSpace.
I would like to know an efficient to way to fetch the data in the following case.
There are two tables say Table1 and Table2 having two common field say contry and pincode and other table "Table3" having key fields of first two tables (DNO, MPNO).
Here is the little glitch, In table3 data, if it is having DNO it wont have MPNO
So when in the selection screen(Pic no2) if the use enter any thing, result should be as follows
**MFID | DNO | MPNO | COUNTRY | PINCODE**
----------
00001 | 10011 | novalue | IN | 4444
00002 | Novalue | 1200 | IN | 5555
00003 | 300 | novalue | US | 9999
( as you can observe if DNO present no MPNO , vice versa )
Please have a look at the pictures for a clear picture :-)
Table Relation:
Selection screen with select options:
The code shouldn't be long.
PSEUDO CODE:
Select queries:
Select * from table3 into it_table3.
Select * from table1 FOR ALL ENTRIES IN it_table3 INTO it_table1
WHERE dno = table3-dno.
Select * from table2 FOR ALL ENTRIES IN it_table3 INTO it_table2
WHERE mpno = table3-mpno.
Loop at internal table 3 and build final table.
LOOP at it_table3 into wa_table3.
IF wa_table3-dno IS NOT INITIAL.
READ it_table1 where dno = wa_table3-dno.
ELSE.
READ it_table2 where mpno = wa_table3-mpno.
ENDIF.
ENDLOOP.
Hope this was the answer you were hoping to find!
Building of efficient select will require information about obligatory fields in your selection screen, as well as about alleged production size of all 3 tables. However, without this information let's assume that table1 and table2 are reference tables and table3 is a transaction table, as onr can assume from their structure. It would be sensible to build selection in a following way:
Selecting data from reference tables. As you said fields DNO/MPNO are mutually exclusive then there will be no hits of country/pincode pair in both reference tables, so JOIN is useless here. However we can merge 2 result sets in single itab without any constraints' violations.
TYPES: BEGIN OF tt_result,
dno TYPE table1-dno,
mpno TYPE table2-mpno,
country TYPE table1-country,
pincode TYPE table1-pincode,
...other field from table3
END OF tt_result.
DATA: itab_result TYPE tt_result.
SELECT dno
FROM table1
INTO CORRESPONDING FIELDS OF TABLE itab_result
WHERE pincode IN so_pincode
AND country IN so_country.
SELECT mpno
FROM table2
APPENDING CORRESPONDING FIELDS OF TABLE itab_result
WHERE pincode IN so_pincode
AND country IN so_country.
FOR ALL ENTRIES addition allows specifying the same table in FOR ALL ENTRIES clause and in INTO clause, so we can fill our result table with absent table3 data by DNO/MPNO key.
SELECT *
FROM table3
INTO CORRESPONDING FIELDS OF TABLE itab_result
FOR ALL ENTRIES IN itab_result
ON itab_result~dno = itab3~dno
AND itab_result_mpno = itab3~mpno.