Hi i have one doubt in postgres. In database have 100 tables . few tables have primary key and foreign key relationship and few tables do not have relationship.
Here I want delete all tables useing delete statement.
When I tried delete statement for all tables that time getting error pk and fk violation.
How will delete fk first and pk tables.
Could you tell me how to write a query to achieve this task I postgres.
You can try the CASCADE option.
https://www.postgresql.org/docs/current/ddl-constraints.html -> item 5.3.5
Related
I have a requirement of deleting records from the Postgres database tables.
We have a Customer table which is the main table, this table contains a primary key which is used in so many other tables as a FOREIGN KEY, I want to delete one of the customers as well as its reference used in other tables. Is there any way to delete the customer from main table as well as from other tables which contains foreign key.
Thanks in Advance.
In the other tables, you want a cascading delete foreign key reference. You can create one in the database using:
alter table othertable add constraint fk_othertable_customerid
foreign key (customerid) references customers(customerid)
on delete cascade;
Note: This assumes that customerid is the name of the column in both tables and that it is already defined in the other tables.
A cascading foreign key constraint does exactly what you specify. When a row is deleted in the reference table, then all related rows are deleted.
If you already have foreign key constraints on customerid, then drop the existing constraint and add the cascading version.
I have to delete records from a table 'project' where internally it has to delete (2000-3000) records from a table 'test_suite' because project_id is foreign key in the test_suite table. The database is Postgres.
I am using the following JPA query to delete the records from table 'test_suite':
testSuiteRepository.deleteInBatchByProjectIdAndAutoGenerated(projectId, true);
This delete is consuming time and delete from the project table ends up throwing an exception that FK constraint violated.
Is there any efficient query for BULK DELETE in POSTGRES?
Database 1 has foreign tables a and b on database 2.
How can we create indexes on these foreign tables a and b. These foreign tables are wrappers over database2.c and database2.d tables respectively, which do have the necessary indexes in place.
How would you create indexes on foreign tables a and b? Is that even possible?
I get a cannot create index on foreign table a - when I try a simple Create Index command in postgres
You cannot create index on a foreign table, instead write a trigger on foreign table and create a local table in postgres such that whenever an insert, update or delete is happening in your foreign table it will be reflected in your local table and index it.
Joining with a foreign table can result to slow query's.
Since indexes are not a option with foreign table, consider making a materialized view on a foreign table . Materialized views do allow indexing
CREATE FOREIGN TABLE members_fdw(...)
CREATE MATERIALIZED VIEW members AS
select * from members_fdw
WITH DATA
CREATE UNIQUE INDEX "member_id" ON members USING btree ("id");
We have two copies of a simple application that is based on SQLite. The application has 10 tables with a variety of relations between the tables. We would like to merge the databases to a single Postgres database with the same schema. We can use Talend to facilitate this, however the issue is that there would be duplicate keys (as both the source databases are independent). Is there a systematic method by which we can insert data into Postgres with the original key plus an offset resulting from loading the first database?
Step 1. Restore the first database.
Step 2. Change foreign keys of all tables by adding the option on update cascade.
For example, if the column table_b.a_id refers to the column table_a.id:
alter table table_b
drop constraint table_b_a_id_fkey,
add constraint table_b_a_id_fkey
foreign key (a_id) references table_a(id)
on update cascade;
Step 3. Update primary keys of the tables by adding the desired offset, e.g.:
update table_a
set id = 10000+ id;
Step 4. Restore the second database.
If you have the possibility to edit the script with database schema (or do the transfer manually with your own script), you can merge steps 1 and 2 and edit the script before the restore (adding the option on update cascade for foreign keys in tables declarations).
I have two tables
Users
Users_Role
I decided to try to add a foreign key as to my understanding it will let me cascade the delete procedure when removing a user from Users (as well as enforce integrity).
So via Management Studio I right clicked my Users_Role table, Design, then went into Relationships. I added a new relationship between the two tables as such:
Foreign Key Base Table: Users_Role
Foreign Key Columns: UserID
Primary/Unique Key Base: Users
Primary/Unique Key columns: ID
When I then try to save, I get the following error:
'Users' table saved successfully
'Users_Role' table
- Unable to create relationship 'FK_Users_Role_Users'.
The ALTER TABLE statement conflicted with the FOREIGN KEY constraint "FK_Users_Role_Users". The conflict occurred in database "db", table "dbo.Users", column 'ID'.
I'm not sure what's going on. Adds the relationship to Users, but not Users_Role? The only thing special about Users_Role is that my primary key consists of two columns, UserID and Role (the only two columns in the table, if that matters). Otherwise, nothing special.
This error means that in your current database, you have entries in the "Users_Role" table which have a "UserID" value that is not present in the Users table as ID.
You first need to find those "rogue" rows and either update or delete them, before you can create the foreign key to enforce referential integrity and avoid such problems in the future.
You can find those by issuing this command:
SELECT * FROM Users_Role
WHERE UserID NOT IN
(SELECT DISTINCT ID FROM Users)