Jah, ma soovin saada regulaarselt e-posti teel teavet uute toodete, praeguste pakkumiste ja uudiste kohta PostgreSQLi kohta. Yes, I would like to receive information about new products, current offers and news about PostgreSQL via e-mail on a regular basis.įurther information can be found in the privacy policy. Wyrażenie zgody na otrzymywanie Newslettera Cybertec drogąĮlektroniczną jest dobrowolne i może zostać w każdej chwili bezpłatnie odwołane.Więcej informacji Tak, chcę regularnie otrzymywać wiadomości e-mail o nowych produktach, aktualnych ofertach i Granting consent to receive the Cybertec Newsletter by electronic means is voluntary and can be withdrawn free of charge at any time.įurther information can be found in the privacy policy. Yes, I would like to receive information about new products, current offers and news about PostgreSQL via e-mail on a regular basis. Granting consent to receive the CYBERTEC Newsletter by electronic means is voluntary and can be withdrawn free of charge at any time.įurther information can be found in the privacy policy. Weitere Informationen finden Sie in der Datenschutzerklärung. Ich kann diese Zustimmung jederzeit widerrufen. Ja, ich möchte regelmäßig Informationen über neue Produkte, aktuelle Angebote und Neuigkeiten rund ums Thema PostgreSQL per E-Mail erhalten. You can now decide whether to not drop the column or whether to drop the view along with the column.įor further reading on views in PostgreSQL, see View Permissions and Row-Level Security in PostgreSQL by Laurenz Albe In this case, PostgreSQL complains that the view cannot be kept around because columns are missing. CASCADE to drop the dependent objects too. View_demo=# ALTER TABLE t_cool_product DROP COLUMN name ĮRROR: cannot drop table t_cool_product column name because other objects depend on itĭETAIL: view v depends on table t_cool_product column name In this case PostgreSQL has to error out because it cannot silently delete the column from the view. Suppose somebody wants to drop a column, on which a view depends on. However, in some cases PostgreSQL has to error out. However, I decided to show how it works behind the scenes, as it might be interesting to know. "pg_rewrite_rel_rulename_index" UNIQUE, btree (ev_class, rulename)īasically this is an internal thing. "pg_rewrite_oid_index" UNIQUE, btree (oid) In the system catalog there is a table called pg_rewrite, which will store a binary representation of the view: What PostgreSQL does behind the scenesīehind the scenes a view is handled by the rewrite system. In other words: Applications relying on the view won’t break just because some other column has changed somewhere. The columns provided by the view will be the same. What is really important and noteworthy here is that the view does not change its output. The same happens when you change the name of a column: The view will not break, become invalid or face deletion. The beauty is that if the name of a table or a column changes, those objects will still have the same object id and therefore there is no problem for the view. Instead, it will keep a binary copy of the definition around, which is largely based on object ids. The reason for that is simple: PostgreSQL does not store the view as string. View_demo=# ALTER TABLE t_product RENAME TO t_cool_product Īs you can see the view will be changed as well. What happens if we simply try to rename the table the view is based on: Note that this is an important thing because it will have serious implications:Ĭolumn | Type | Collation | Nullable | Default | Storage | Description PostgreSQL has silently replaced the “*” with the actual column list. In the following listing you can see that the view definition does not contain a “*” anymore. The important thing here to see is how PostgreSQL handles the view. View_demo=# CREATE VIEW v AS SELECT * FROM t_product The first thing to do in order to get our demo going is to create a view: Id | integer | | not null | nextval('t_product_id_seq'::regclass) Here is the layout of the table:Ĭolumn | Type | Collation | Nullable | Default My table has just three simple columns and does not contain anything special. To show what PostgreSQL will do, I created a simple table: What happens if the data structure of the underlying table changes? CREATE VIEW in PostgreSQL The question many people now ask if: If a view is based on a table. The fields in a view are fields from one or more real tables in the database. It is an abstraction layer, which allows to access the result of a more complex SQL fast an easily. In PostgreSQL, a view is a virtual table based on an SQL statement.
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