![]() To change a view's schema, you must also have CREATE privilege on the new schema. ![]() ) You must own the view to use ALTER VIEW. (If you want to modify the view's defining query, use CREATE OR REPLACE VIEW. It will drop any additional attributes of the view, though. Description ALTER VIEW changes various auxiliary properties of a view. This will never delete any data of the underlying tables. ALTER TABLE test ALTER COLUMN valsum TYPE int4 generated always AS (vala valb 1) stored ALTER TABLE test ALTER COLUMN valsum SET generated always AS (vala valb 1) stored but both give syntax errors. You have to DROP the old and CREATE a new view. In this article, I will let you know, how to alter type of a column used by view in PostgreSQL. Once a table is created, you can modify any of the table properties following. We can now make use of ALTER to change the definition of an existing object, be it a table, column, function, view etc. However, if you want to change data types of resulting columns (like in the case at hand), CREATE OR REPLACE VIEW is not possible. The ALTER statements are used to modify properties of existing objects. Use CREATE OR REPLACE VIEW to change the query - it will preserve any additional attributes. The ALTER VIEW statement can only change auxiliary attributes of a view. If you change underlying objects, you may need to change depending views, too. Very often when you try to ALTER TABLE or REPLACE VIEW it tells you that you cannot do it, because there's another object (typically a view or materialized view), which depends on the one you want to modify. To resolve the error, we require to drop the view, run the alter statement and recreate the view but enclosing the these statements in a transaction. PostgreSQL allows running DDL statements in a transaction. (That's why you can alter views with an ALTER TABLE command.) You can GRANT privileges to it, add comments or even define column defaults (useful for a rule ON INSERT TO my_view DO INSTEAD.). PostgreSQL will throw the same error if you attempt to change any column definition of the table. For historical reasons, ALTER TABLE can be used with views too but the only variants of ALTER TABLE that are allowed with views are equivalent to the ones. Views are implemented as special tables with a rule ON SELECT TO my_view DO INSTEAD. Detailed explanationĪ view in PostgreSQL is not just an "alias to subquery". You can change or drop that constraint any time without touching depending objects like views and without forcing Postgres to write new rows in the table due to the change of type (which isn't always necessary any more in modern version of Postgres). ![]() If you really want to enforce a maximum length, create a CHECK constraint: ALTER TABLE monkeyĪDD CONSTRAINT monkey_name_len CHECK (length(name) < 101) PostgreSQL supports the ALTER TABLE statement to modify the structure of the existing tables. Read about these data types in the manual. An ALTER TABLE statement is part of DDL, and is for altering a table schema only well look at. If the column fails either of those checks, the alter table command will fail.To avoid the problem altogether use the data type text or varchar / character varying without a length specifier instead of character varying(n). Existing tables can be altered with an ALTER TABLE statement. It is important to note that we can only make an existing column a primary key if that column has no null values and no duplicates. PostgreSQL allows you to set a default value for a column name, change the view’s schema, set or reset options of a view. We can inspect our table again and see that in addition to the uniqueness constraint we already had, the employee number now has a not null constraint, and an index. alter table users add primary key (employee_number) We then specify our action, which is "add primary key", and we pass the name of the column we are making our new primary key. Indexes and table constraints involving the column will be automatically dropped as well. DROP COLUMN This form drops a column from a table. There are several subforms: ADD COLUMN This form adds a new column to the table using the same syntax as CREATE TABLE. To make an existing column the primary key, we can use the "alter table" command, passing the table we're dealing with, which for us is "users". ALTER TABLE changes the definition of an existing table. \d usersĪs you can see we currently have one constraint, which is asserting that the employee number is unique. ERROR: cannot alter type of a column used by a view or rule This is because there are materialized views derived from that table. We can also inspect the table to see the current columns and constraints. We can select from this table and see that we already have data: select * from users In this example, we're going to be dealing with a dummy database that has a table called users, with the columns name, and employee number. To change the structure of an existing table, you use PostgreSQL ALTER TABLE statement.
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