I have a database with 2 tables, foo and foo_trash.
Both have the same structure with an id (primary key), and a title. foo_trash gets populated with data copied from foo with a statement like this:
INSERT INTO foo_trash (SELECT * FROM foo WHERE id = 253)
I would like to add a constraint on the table foo_trash so that no rows may be inserted into foo_trash if the same pair id and title is not present in foo.
How do I write that?
Given the table foo:
create table foo (
id int,
title varchar(50),
primary key (id, title)
);
Define the table foo_trash to reference the two columns you mentioned:
create table foo_trash (
id int primary key,
title varchar(50),
FOREIGN KEY (id, title) REFERENCES foo (id, title)
);
Now you can insert data into foo:
insert into foo values (1, 'title1');
insert into foo values (2, 'title2');
insert into foo values (3, 'title3');
insert into foo values (253, 'title253');
If you try to insert a row into foo_trash that doesn't exist in foo, you will receive an error:
insert into foo_trash values (4, 'title4');
Output:
ERROR: insert or update on table "foo_trash" violates foreign key constraint "foo_trash_id_title_fkey"
DETAIL: Key (id, title)=(4, title4) is not present in table "foo".
You can insert a row in foo_trash that exists in foo:
insert into foo_trash values (3, 'title3');
And you can do your insert into foo_trash as select from foo successfully, assuming that id exists:
INSERT INTO foo_trash (SELECT * FROM foo WHERE id = 253);
Related
Suppose the following structure:
CREATE SCHEMA IF NOT EXISTS my_schema;
CREATE TABLE IF NOT EXISTS my_schema.user (
id SERIAL PRIMARY KEY,
tag_id BIGINT NOT NULL
);
CREATE TABLE IF NOT EXISTS my_schema.conversation (
id SERIAL PRIMARY KEY,
user_ids BIGINT[] NOT NULL
);
INSERT INTO my_schema.user VALUES
(1, 55555),
(2, 77777);
INSERT INTO my_schema.conversation VALUES
(1, '{1,2}');
I can pull out the my_schema.conversation records if I know the my_schema.user.id values:
SELECT *
FROM my_schema.conversation
WHERE user_ids #> '{1}'
The above works, but I need to use my_schema.user.tag_id instead of my_schema.user.id:
How can I do this?
Fiddle
You would have to join the two tables on the array values
SELECT *
FROM my_schema.user u
JOIN my_schema.conversation c
ON u.id = any(c.chat_ids)
WHERE u.tag_id=55555;
I have table tariffs, with two columns: (tariff_id, reception)
I have table users, with two columns: (user_id, reception)
And I have table users_tariffs with two columns: (user_id, tariff_id).
I want to prevent situation when tariff from one reception is assigned to user from another reception. How can I do that?
E.G
Users:
user_id | reception
Putin | Russia
Trump | USA
Tariffs:
tariff_id | reception
cheap | USA
expensive | Russia
Wrong situation at users_tariffs, because Cheap tariff is for USA only:
user_id | tariff_id
Putin | Cheap
SOLUTION 1: FOREIGN KEY CONSTRAINTS
I am assuming the following table definitions.
In particular, the composite key in user_tariffs makes this a many-to-many relationship between users and tariffs.
CREATE TABLE tariffs (tariff_id int NOT NULL PRIMARY KEY,
reception text NOT NULL);
CREATE TABLE users (user_id int NOT NULL PRIMARY KEY,
reception text NOT NULL);
CREATE TABLE user_tariffs (tariff_id int NOT NULL REFERENCES tariffs (tariff_id),
user_id int NOT NULL REFERENCES users (user_id),
PRIMARY KEY (tariff_id, user_id));
You probably need a combination of all three columns somewhere, so let's create this:
ALTER TABLE user_tariffs ADD COLUMN reception text;
UPDATE user_tariffs a
SET reception = b.reception
FROM (SELECT * FROM tariffs) b
WHERE a.tariff_id = b.tariff_id;
ALTER TABLE user_tariffs ALTER COLUMN reception SET NOT NULL;
Now we can use FOREIGN KEY REFERENCES (user_id, reception) into users.
CREATE UNIQUE INDEX ON tariffs (tariff_id, reception);
ALTER TABLE user_tariffs ADD FOREIGN KEY (tariff_id, reception)
REFERENCES tariffs (tariff_id, reception);
In addition, we can use FK REFs (tariff_id, reception) into tariffs.
CREATE UNIQUE INDEX ON users (user_id, reception);
ALTER TABLE user_tariffs ADD FOREIGN KEY (user_id, reception)
REFERENCES users (user_id, reception);
Populate with data:
INSERT INTO users VALUES (1, 'cheap'), (2, 'expensive');
INSERT INTO tariffs VALUES (1, 'cheap'), (2, 'expensive');
Now assume we have the following data (user_id, tariff_id) to insert:
WITH data (user_id, tariff_id)
AS (VALUES (1, 2), (2, 1)), -- here is your application data
datas (user_id, tariff_id, reception)
AS (SELECT user_id,
tariff_id,
(SELECT u.reception -- reception calculated by user
FROM users u
WHERE u.user_id = d.user_id)
FROM data d)
INSERT INTO user_tariffs SELECT * FROM datas ;
Then you cannot insert the data, because you can only add (1, 1) or (2, 2) with the same reception, but not (1, 2) or (2, 1) with different reception's. The error message is:
ERROR: insert or update on table "user_tariffs" violates foreign key constraint "user_tariffs_user_id_fkey1"
DETAIL: Key (user_id, reception)=(2, cheap) is not present in table "users".
But you can insert with data AS VALUES (1, 1), (2, 2).
I think the FOREIGN KEY CONSTRAINT solution is to be preferred.
Please describe your functional dependencies, if you want better table designs.
SOLUTION 2: TRIGGER
-- DROP TABLE user_tariffs CASCADE;
-- DROP TABLE users CASCADE;
-- DROP TABLE tariffs CASCADE;
CREATE TABLE tariffs (tariff_id int NOT NULL PRIMARY KEY,
reception text NOT NULL);
CREATE TABLE users (user_id int NOT NULL PRIMARY KEY,
reception text NOT NULL);
CREATE TABLE user_tariffs (tariff_id int NOT NULL REFERENCES tariffs (tariff_id),
user_id int NOT NULL REFERENCES users (user_id),
PRIMARY KEY (tariff_id, user_id));
INSERT INTO users VALUES (1, 'cheap'), (2, 'expensive');
INSERT INTO tariffs VALUES (1, 'cheap'), (2, 'expensive');
-- table user_tariffs (user_id, tariff_id) only, without reception column.
Create a function with return type trigger:
CREATE OR REPLACE FUNCTION check_reception()
RETURNS trigger AS $$
DECLARE valid boolean := false;
BEGIN
SELECT (SELECT u.reception FROM users u WHERE u.user_id = NEW.user_id)
= (SELECT t.reception FROM tariffs t WHERE t.tariff_id = NEW.tariff_id)
INTO valid FROM user_tariffs ;
IF valid = false
THEN RAISE EXCEPTION '(user, tariff, reception) invalid.';
END IF;
RETURN NEW;
END; $$ LANGUAGE plpgsql ;
and register it:
CREATE TRIGGER reception_trigger
AFTER INSERT OR UPDATE ON user_tariffs
FOR EACH ROW EXECUTE PROCEDURE check_reception();
Now try to insert (1, 2), which would be (cheap, expensive) and is not allowed:
INSERT INTO user_tariffs VALUES (1, 2);
ERROR: (user, tariff, reception) invalid.
KONTEXT: PL/pgSQL function check_reception() line 7 at RAISE
But we can insert (1, 1), which is (cheap, cheap) without problem:
INSERT INTO user_tariffs VALUES (1, 1);
SELECT * FROM user_tariffs;
Remark
Triggers are not the best solution here, in my opinion. Try to avoid triggers, if possible. They can have side effects (transactions etc). Check StackOverflow for further details :)
I have the following three tables:
Please note that the below DDL came models generated by Django then grabbed out of Postgresql after they were created. So modifying the tables is not an option.
CREATE TABLE "parentTeacherCon_grade"
(
id INTEGER PRIMARY KEY NOT NULL,
"currentGrade" VARCHAR(2) NOT NULL
);
CREATE TABLE "parentTeacherCon_parent"
(
id INTEGER PRIMARY KEY NOT NULL,
name VARCHAR(50) NOT NULL,
grade_id INTEGER NOT NULL
);
CREATE TABLE "parentTeacherCon_teacher"
(
id INTEGER PRIMARY KEY NOT NULL,
name VARCHAR(50) NOT NULL
);
CREATE TABLE "parentTeacherCon_teacher_grade"
(
id INTEGER PRIMARY KEY NOT NULL,
teacher_id INTEGER NOT NULL,
grade_id INTEGER NOT NULL
);
ALTER TABLE "parentTeacherCon_parent" ADD FOREIGN KEY (grade_id) REFERENCES "parentTeacherCon_grade" (id);
CREATE INDEX "parentTeacherCon_parent_5c853be8" ON "parentTeacherCon_parent" (grade_id);
CREATE INDEX "parentTeacherCon_teacher_5c853be8" ON "parentTeacherCon_teacher" (grade_id);
ALTER TABLE "parentTeacherCon_teacher_grade" ADD FOREIGN KEY (teacher_id) REFERENCES "parentTeacherCon_teacher" (id);
ALTER TABLE "parentTeacherCon_teacher_grade" ADD FOREIGN KEY (grade_id) REFERENCES "parentTeacherCon_grade" (id);
CREATE UNIQUE INDEX "parentTeacherCon_teacher_grade_teacher_id_20e07c38_uniq" ON "parentTeacherCon_teacher_grade" (teacher_id, grade_id);
CREATE INDEX "parentTeacherCon_teacher_grade_d9614d40" ON "parentTeacherCon_teacher_grade" (teacher_id);
CREATE INDEX "parentTeacherCon_teacher_grade_5c853be8" ON "parentTeacherCon_teacher_grade" (grade_id);
My Question is: How do I write an insert statement (or statements) where I do not have keep track of the IDs? More specifically I have a teacher table, where teachers can teach relate to more than one grade and I am attempting to write my insert statements to start populating my DB. Such that I am only declaring a teacher's name, and grades they relate to.
For example, if I have a teacher that belong to only one grade then the insert statement looks like this.
INSERT INTO "parentTeacherCon_teacher" (name, grade_id) VALUES ('foo bar', 1 );
Where grades K-12 are enumerated 0,12
But Need to do something like (I realize this does not work)
INSERT INTO "parentTeacherCon_teacher" (name, grade_id) VALUES ('foo bar', (0,1,3) );
To indicate that this teacher relates to K, 1, and 3 grades
leaving me with this table for the parentTeacherCon_teacher_grade
+----+------------+----------+
| id | teacher_id | grade_id |
+----+------------+----------+
| 1 | 3 | 0 |
| 2 | 3 | 1 |
| 3 | 3 | 3 |
+----+------------+----------+
This is how I can currently (successfully) insert into the Teacher Table.
INSERT INTO public."parentTeacherCon_teacher" (id, name) VALUES (3, 'Foo Bar');
Then into the grade table
INSERT INTO public.parentTeacherCon_teacher_grade (id, teacher_id, grade_id) VALUES (1, 3, 0);
INSERT INTO public.parentTeacherCon_teacher_grade (id, teacher_id, grade_id) VALUES (2, 3, 1);
INSERT INTO public.parentTeacherCon_teacher_grade (id, teacher_id, grade_id) VALUES (3, 3, 3);
A bit more information.
Here is a diagram of the database
Other things I have tried.
WITH i1 AS (INSERT INTO "parentTeacherCon_teacher" (name) VALUES ('foo bar')
RETURNING id) INSERT INTO "parentTeacherCon_teacher_grade"
SELECT
i1.id
, v.val
FROM i1, (VALUES (1), (2), (3)) v(val);
Then I get this error.
[2016-08-10 16:07:46] [23502] ERROR: null value in column "grade_id" violates not-null constraint
Detail: Failing row contains (6, 1, null).
If you want to insert all three rows in one statement, you can use:
INSERT INTO "parentTeacherCon_teacher" (name, grade_id)
SELECT 'foo bar', g.grade_id
FROM (SELECT 0 as grade_id UNION ALL SELECT 1 UNION ALL SELECT 3) g;
Or, if you prefer:
INSERT INTO "parentTeacherCon_teacher" (name, grade_id)
SELECT 'foo bar', g.grade_id
FROM (VALUES (0), (2), (3)) g(grade_id);
EDIT:
In Postgres, you can have data modification statements as a CTE:
WITH i as (
INSERT INTO public."parentTeacherCon_teacher" (id, name)
VALUES (3, 'Foo Bar')
RETURNING *
)
INSERT INTO "parentTeacherCon_teacher" (name, teacher_id, grade_id)
SELECT 'foo bar', i.id, g.grade_id
FROM (VALUES (0), (2), (3)) g(grade_id) CROSS JOIN
i
I used a COPY command to load a bunch of data in the database and then created the primary keys and foreign keys afterwards.
When I created one of the foreign keys, I got the error message: violates foreign key constraint "some_fkey" . Is there a way that I can raise the log level so that I can see on which row this violation happened so that I can go back and debug/check the data?
A workaround:
Suppose your tables look like this:
CREATE TABLE a (a_id INTEGER PRIMARY KEY, x TEXT);
CREATE TABLE b (b_id INTEGER PRIMARY KEY, a_id INTEGER, x TEXT);
And the creation of the following foreign key gives you the error:
ALTER TABLE b ADD CONSTRAINT a_a_id_fk FOREIGN KEY (a_id) REFERENCES a (a_id) ON UPDATE CASCADE ON DELETE RESTRICT;
You could join the two tables to get the problematic rows:
SELECT b_id, a_id FROM b LEFT JOIN a USING (a_id) WHERE a.a_id IS NULL;
Let's see!
Sample data:
INSERT INTO a VALUES (1, 'a'), (2, 'b'), (3, 'c');
INSERT INTO b VALUES (1, 1, 'x'), (2, 3, 'y'), (3, 1000, 'z');
And the result of the query above:
b_id | a_id
------+------
3 | 1000
(1 row)
I want to "dynamically" create the result columns in a PostgreSQL query. I have these tables:
CREATE SEQUENCE users_id;
CREATE TABLE users (
id INT PRIMARY KEY NOT NULL DEFAULT NEXTVAL('users_id'),
name VARCHAR(128) NOT NULL
);
CREATE SEQUENCE quota_rules_id;
CREATE TABLE quota_rules (
id INT PRIMARY KEY NOT NULL DEFAULT NEXTVAL('quota_rules_id'),
user_id INT REFERENCES users(id),
rule VARCHAR(255) NOT NULL
);
CREATE INDEX user_id_index ON quota_rules(user_id);
INSERT INTO users (name) VALUES ('myname'); -- id=1
INSERT INTO quota_rules (user_id, rule) VALUES (1, 'a');
INSERT INTO quota_rules (user_id, rule) VALUES (1, 'b');
INSERT INTO quota_rules (user_id, rule) VALUES (1, 'c');
And want a query that returns this (1 row):
SELECT ............ user_id = 1;
name | quota_rule | quota_rule2 | quota_rule3
myname | a | b | c
Check out the crosstab function of the tablefunc module