So, I've got two tables - PLUTO (pieces of land), and NYZMA (rezoning boundaries). They look like:
pluto nyzma
id | geom name | geom
-------------------- -------------------
1 | MULTIPOLYGON(x) A | MULTIPOLYGON(a)
2 | MULTIPOLYGON(y) B | MULTIPOLYGON(b)
And I want it to spit out something like this, assuming that PLUTO record 1 is in multipolygons A and B, and PLUTO record 2 is in neither:
pluto_id | nyzma_id
-------------------
1 | [A, B]
2 |
How do I, for every PLUTO record's corresponding geometry, cycle through each NYZMA record, and print the names of any whose geometry matches?
Join the two tables using the spatial function ST_Contains. Than use GROUP BY and ARRAY_AGG in the main query:
WITH subquery AS (
SELECT pluto.id, nyzma.name
FROM pluto LEFT OUTER JOIN nyzma
ON ST_Contains(nyzma.geom, pluto.geom)
)
SELECT id, array_agg(name) FROM subquery GROUP BY id;
Related
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.
Let's say I have this table:
id | status | type
----+--------+----------
1 | new | car
2 | new | boat
3 | used | car
4 | new | car
and I wanted to count all the new vehicles, and the number of cars in one go, how to do that?
I tried this:
SELECT COUNT(status='new'), COUNT(type='car') FROM table;
but it always counts to 4 (the total amount of rows). The only thing I can think of is using a CASE inside the COUNT, but is there a cleaner way?
You could use FILTER to perform conditional aggregation:
SELECT COUNT(*) FILTER(WHERE status='new'), COUNT(*) FILTER(WHERE type='car')
FROM tab;
Alternatively SUM:
SELECT SUM((status='new')::int), SUM((type='car')::int) FROM table;
Is there a way to find duplicate entries in a data set using JPA?
| id | text |
-------------
| 1 | foo |
| 2 | bar |
| 3 | foo |
I want to have only entries 1 & 3 in my set.
I can't make it unique on this field.
—
DISTINCT would give me rows 1 & 2.
If it’s a query, a join with the same table? I’m not sure how that would work. I couldn’t get group by to function.
Edited
I believe you can use the following syntax without inner query:
SELECT id, text, COUNT(*) FROM entity GROUP BY text HAVING COUNT(*) > 1
You can apply common practice from SQL to JPQL with the following query:
SELECT e FROM Entity e WHERE e.text IN (SELECT text FROM Entity d GROUP BY text HAVING COUNT(*)>1.
A sub-query is required so you'd need an index on text column for it to be efficient.
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.
So I have this table:
create table test (
id integer,
rank integer,
image varchar(30)
);
Then some values:
id | rank | image
---+------+-------
1 | 2 | bbb
1 | 3 | ccc
1 | 1 | aaa
2 | 3 | c
2 | 1 | a
2 | 2 | b
I want to group them by id and concatenate the image name in the order given by rank. In mySQL I can do this:
select id,
group_concat( image order by rank asc separator ',' )
from test
group by id;
And the output would be:
1 aaa,bbb,ccc
2 a,b,c
Is there a way I can have this in postgresql?
If I try to use array_agg() the names will not show in the correct order and apparently I was not able to find a way to sort them. (I was using postgres 8.4 )
In PostgreSQL 8.4 you cannot explicitly order array_agg but you can work around it by ordering the rows passed into to the group/aggregate with a subquery:
SELECT id, array_to_string(array_agg(image), ',')
FROM (SELECT * FROM test ORDER BY id, rank) x
GROUP BY id;
In PostgreSQL 9.0 aggregate expressions can have an ORDER BY clause:
SELECT id, array_to_string(array_agg(image ORDER BY rank), ',')
FROM test
GROUP BY id;