Making correct use of foreign keys will definitely improve the quality of your database applications, so you are strongly encouraged to learn about them. ![]() We will not go beyond this simple example in this tutorial, but just refer you to Chapter 5 for more information. ![]() The behavior of foreign keys can be finely tuned to your application. INSERT INTO weather VALUES ('Berkeley', 45, 53, 0.0, '') ĮRROR: insert or update on table "weather" violates foreign key constraint "weather_city_fkey"ĭETAIL: Key (city)=(Berkeley) is not present in table "cities". But I dont think I can call pgrestore.exe from inside psql.exe after deferring the constraints. In SO I found something interesting: deferring constraint checking to commit time. The new declaration of the tables would look like this:Ĭity varchar(80) references cities(name), Is there a way to disable the constraints and all foreign keys, for all tables, before I call pgrestore.exe, and afterwards, re-enable the constraints and foreign keys. Its a data integrity enforcement tool, not a performance tool. The only impact removing one can have on performance is a performance improvement due to the removal of foreign key checks. This approach has a number of problems and is very inconvenient, so PostgreSQL can do this for you. At time of writing (PostgreSQL 9.4 and below), PostgreSQLs optimiser doesnt use foreign key constraints to prove anything or allow for extra optimisations. In simplistic database systems this would be implemented (if at all) by first looking at the cities table to check if a matching record exists, and then inserting or rejecting the new weather records. This is called maintaining the referential integrity of your data. I couldnt figure out how to change the action. Consider the following problem: You want to make sure that no one can insert rows in the weather table that do not have a matching entry in the cities table. To generate a script to drop constraints: SELECT 'ALTER TABLE ''nspname''.''relname'' DROP CONSTRAINT ''conname'' ' FROM pgconstraint INNER JOIN pgclass ON conrelidpgclass. ![]() Start the applications and check if everything is in place. This is called maintaining the referential integrity of your data. Consider the following problem: You want to make sure that no one can insert rows in the weather table that do not have a matching entry in the cities table. Use the generated addingConstraints.sql SQL script to ADD the constraints back to the database. Foreign Keys Recall the weather and cities tables from Chapter 2. Do the necessary changes in the database. Recreate all foreign keys in all tables as deferrable (batch) I want to make all foreign keys in my database deferrable. CASCADE to drop the dependent objects too.Recall the weather and cities tables from Chapter 2. Use the generated droppingConstraints.sql SQL script to DROP the constraints. PostgreSQL said: cannot drop constraint unique_id_checkpoint on table checkpoint because other objects depend on itĭetail: constraint fk_vehiculo_checkpoint_idpunto on table vehiculo_checkpoint depends on index unique_id_checkpoint CASCADE to drop the dependent objects too. The constraint name is optional if you do not specify it, PostgreSQL will give the name as per the default naming convention. DROP TABLE command, 181 columns, 298-302 constraints, 277 CHECK constraint, 278 CREATE TABLE command, 277-278 DEFAULT constraint, 280 foreign keys. But I cannot delete the UNIQUE CONSTRAINT as it is referenced by 2 FKs, as in the following messages: alter table checkpoint drop constraint unique_id_checkpoint ĮRROR: cannot drop constraint unique_id_checkpoint on table checkpoint because other objects depend on itĭETAIL: constraint fk_vehiculo_checkpoint_idpunto on table vehiculo_checkpoint depends on index unique_id_checkpointĬonstraint fk_geocelda_punto on table geocelda depends on index unique_id_checkpointĬonstraint fk_checkpoin_id on table ruta_checkpoint depends on index unique_id_checkpoint Allows users to create and drop databases and tables. ![]() I have detected a duplicate index on an id field on one of our tables, as that column is the PK, but there's also a separate UNIQUE index on such column, which is useless. As far I know the only way of dropping primary key in postgresql is: ALTER TABLE schema.tableName DROP CONSTRAINT constraintname the constraint name by default is tableNamepkey.However sometimes if table is already renamed I can’t get the original table name to construct right constraint name. Oracle, Sybase, Informix, Postgres and SQL Server use SQL as their Standard Database Language.
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