I'm trying to create a policy in postgres that results in a column reference "person_id" is ambiguous.
To make a small, similar example let's describe 3 tables: person, group and group_member.
Person has: id, name
Group has: id, person_id and name
Group Member has: id, person_id, group_id
I've simplified my policy, but the relevant portion looks something like this:
CREATE POLICY insert_group_member ON public."group" FOR INSERT TO user_role WITH CHECK (
EXISTS (
SELECT * FROM "group" AS g
LEFT JOIN "group_member" AS gm ON
g.person_id = gm.person_id
AND g.id = gm.group_id
WHERE
g.id = id AND
gm.person_id = person_id AND
g.members_can_invite = TRUE
)
);
person_id in this case can refer to group.person_id or group_member.person_id from the sub-select, but what I really want it to be is the person_id coming from the "with check". This generally, works in other places.
Question: is there way to clearly specify that the person_id column comes from the policy and not from the select or the join. Note: I'd have expected that aliasing the table names solves this problem, but it seems to have not.
You should qualify all column references, like this:
...
WHERE g.id = "group".id
AND gm.person_id = "group".person_id
Related
I have got two tables:
create table student
(
studentid bigint primary key not null,
name varchar(200) not null
);
create table courseregistration
(
studentid bigint not null,
coursenamename varchar(200) not null,
isfinished boolean default false
);
--insert some data
insert into student values(1,'Dave');
insert into courseregistration values(1,'SQL',true);
Student is fetched with id, so it should be always returned in the result. Entry in the courseregistration is optional and should be returned if there are matching rows and those matching rows should be filtered on isfinished=false. This means I want to get the course regsitrations that are not finished yet. Tried to outer join student with courseregistration and filter courseregistration on isfinished=false. Note that, I still want to retrieve the student.
Trying this returns no rows:
select * from student
left outer join courseregistration using(studentid)
where studentid = 1
and courseregistration.isfinished = false
What I'd want in the example above, is a result set with 1 row student, but course rows null (because the only example has the isfinished=true). One more constraint though. If there is no corresponding row in courseregistration, there should still be a result for the student entry.
This is an adjusted example. I can tweak my code to solve the problem, but I really wonder, what is the "correct/smart way" of solving this in postgresql?
PS I have used the (+) in Oracle previously to solve similar issues.
Isn't this what you are looking for :
select * from student s
left outer join courseregistration cr
on s.studentid = cr.studentid
and cr.isfinished = false
where s.studentid = 1
db<>fiddle here
I need to write a sql code that probably is very simple but I am very new to it.
I need to find all the records from one table that have matching id (but no more than one) from the other table. eg. one table contains records of the employees and the second one with employees' telephone numbers. i need to find all employees with only one telephone no
Sample data would be nice. In absence of:
SELECT
employees.employee_id
FROM
employees
LEFT JOIN
(SELECT distinct on(employee_id) employee_id FROM emp_phone) AS phone
ON
employees.employee_id = phone.employee_id
WHERE
phone.employee_id IS NOT NULL;
You need a join of the 2 tables, group by employee and the condition in the having clause:
SELECT e.employee_id, e.name
FROM employees e INNER JOIN numbers n
ON e.employee_id = n.employee_id
GROUP BY e.employee_id, e.name
HAVING COUNT(*) = 1;
If there can be more than a few numbers per employee in the table with the employees' telephone numbers (calling it tel), then it's cheaper to avoid GROUP BY and HAVING which has to process all rows. Find employees with "unique" numbers using a self-anti-join with NOT EXISTS.
While you don't need more than the employee_id and their unique phone number, you don't even have to involve the employee table at all:
SELECT *
FROM tel t
WHERE NOT EXISTS (
SELECT FROM tel
WHERE employee_id = t.employee_id
AND tel_number <> t.tel_number -- or use PK column
);
If you need additional columns from the employee table:
SELECT * -- or any columns you need
FROM (
SELECT employee_id AS id, tel_number -- or any columns you need
FROM tel t
WHERE NOT EXISTS (
SELECT FROM tel
WHERE employee_id = t.employee_id
AND tel_number <> t.tel_number -- or use PK column
)
) t
JOIN employee e USING (id);
The column alias in the subquery (employee_id AS id) is just for convenience. Then the outer join condition can be USING (id), and the ID column is only included once in the result, even with SELECT * ...
Simpler with a smart naming convention that uses employee_id for the employee ID everywhere. But it's a widespread anti-pattern to use employee.id instead.
Related:
JOIN table if condition is satisfied, else perform no join
I have a composite type that looks like
CREATE TYPE member AS (
id BIGINT,
type CHAR(1)
);
I have a table that relies on this member type with an array.
CREATE TABLE relation (
id BIGINT PRIMARY KEY,
members member[]
);
I have three other tables each with a different schema (but having common id field)
CREATE TABLE table_x (
id BIGINT PRIMARY KEY,
some_text TEXT
);
CREATE TABLE table_y (
id BIGINT PRIMARY KEY,
some_int INT
);
CREATE TABLE table_z (
id BIGINT PRIMARY KEY,
some_date TIMESTAMP
);
type field in member type is just one character to find out table that specific member belongs to. A row in relation table can have a mix of different types.
I have a scenario which requires returning relation ids with at least one member fulfilling a certain condition based on it's type (let's say for x => some_text is not empty or y => some_int is greater than 10 or z => some_date is a week is from now).
I can implement this scenario on the application side by making multiple requests to the database:
unnest relation table
collect member data per relation
make new requests to find out relations
I am wondering if there is a way to map column values to table names and join them.
Assumption
I´m assuming that relation.members array does not have more than one member element of the same type. Correct?
Query to try
with unnested_members as (
-- Unnest members array
select id, unnest(members) members
from relation
)
, members_joined as (
-- left join on a per type basis with table_x, table_y and table_z.
select r.id, (r.members).id idext, (r.members).type,
x.some_text, y.some_int, z.some_date -- more types, more columns here
from unnested_members r
left join table_x x on (x.id = (r.members).id and (r.members).type = 'x')
left join table_y y on (y.id = (r.members).id and (r.members).type = 'y')
left join table_z z on (z.id = (r.members).id and (r.members).type = 'z')
-- More types, more tables to left join
)
select id,
max(some_text) some_text, -- use max() to get not null value for this id
max(some_int) some_int, -- use max() to get not null value for this id
max(some_date) some_date -- use max() to get not null value for this id
-- more types, more max() columns here
from members_joined
group by id -- get one row per relation.id with data from joined table_* columns
If you need to include more tables then you have to include these tables in the left join part, include the column in the select list and in the max() section as well.
#JNevill had a good point about this database design. Although this approach may not seem optimal, it keeps the table definitions clearly separate without any relations in between them. Also the size of relation table is fairly small compared to other three tables.
I solved the problem by simply fetching rows per type and merging them:
SELECT relation.* FROM relation, UNNEST(relation.members) member INNER JOIN table_x ON member.id = table_x.id WHERE member.type = 'x' AND table_x.some_text = 'some text value'
UNION
SELECT relation.* FROM relation, UNNEST(relation.members) member INNER JOIN table_y ON member.id = table_y.id WHERE member.type = 'y' AND table_y.some_int = 123
UNION
SELECT relation.* FROM relation, UNNEST(relation.members) member INNER JOIN table_z ON member.id = table_z.id WHERE member.type = 'z' AND table_z.some_date > '2017-01-11 00:00:00';
This is a Firebird database.
First Table
Contacts
Company_ID - job_title
Second Table
Client_id - Co_name
In contacts, I want to the job_title field to contain the co_name.
client_id and company_id are the same.
Co_name correspond to company_id as well as client_id.
this:
UPDATE Contacts
SET Contacts.Job_title = Clients.co_name
WHERE
company_id IN (
SELECT
client_id
FROM
clients
JOIN Contacts c ON Client_id = company_id
WHERE
record_status = 'A'
)
gives me an error as cannot find (clients.co_name)
this other option:
UPDATE Contacts
JOIN Clients ON Clients.Client_id = Contacts.Client_id
SET Contacts.Job_title = Clients.Client_name
gives me an error on JOIN
Any other ideas please?
Thank you all
Possibly already answered here: Update records in one table using another table's records as WHERE parameters - looks like it should work, but I'm not a Firebird expert.
The code from that answer (but look for more context, and alternative answers):
UPDATE Table1
SET Column1 = NULL
WHERE NOT EXISTS
(SELECT 1
FROM Table2
WHERE Table2.Column2 = Table1.Column2)
(couldn't flag question as duplicate because that question has no upvoted or accepted answer)
I mean the following:
I have 2 parent tables :
table1
id PRIMARY KEY
name TEXT
table2
id PRIMARY KEY
...
and a child table, used fo n-n Relations :
table_child
id PRIMARY KEY
id_1 INT
id_2 INT
where id_1 and id_2 in table_child refer to the column id in table1 and table2.
Now : i often perform request, with a join between table_1 and table_child ON table1.id = table_child.id1, only because i need the value of the column table1.name.
I'm wondering if there is a way to avoid these joins, and declare somehow a "pseudo" column name in table_child, which would not be a real column, but a link to the corresponding column in table_1, so that :
* I can acces the value through table_child.name
* But it is always synchronized with the value table1.name
I hope my explanation was understandable...
Further to my comment above, the answer you're really looking for is something like:
CREATE VIEW
table1_child_view AS
SELECT
table1.name,
table1_child.*
FROM
table1_child
INNER JOIN
table1 ON
table1.id = table1_child.id_1
Then you can run your queries on the new view, such as:
SELECT name FROM table1_child_view WHERE ...