Comments are attached to a column using the comment statement: create table session_log ( userid int not null, phonenumber int ); comment on column session_log.userid is ‘The user ID’; comment on column session_log.phonenumber is ‘The phone number including the area code’; You can also add a comment to the table: comment on table session_log is … Read more
Your understanding is correct. You would do this in many cases. One example is in a relationship like OrderHeader and OrderDetail. The PK in OrderHeader might be OrderNumber. The PK in OrderDetail might be OrderNumber AND LineNumber. If it was either of those two, it would not be unique, but the combination of the two … Read more
Update: SQLite 2021-03-12 (3.35.0) now supports DROP COLUMN. The FAQ on the website is still outdated. From: http://www.sqlite.org/faq.html: (11) How do I add or delete columns from an existing table in SQLite. SQLite has limited ALTER TABLE support that you can use to add a column to the end of a table or to change … Read more
Just remove COLUMN from ADD COLUMN ALTER TABLE Employees ADD EmployeeID numeric NOT NULL IDENTITY (1, 1) ALTER TABLE Employees ADD CONSTRAINT PK_Employees PRIMARY KEY CLUSTERED ( EmployeeID ) WITH( STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
My MySQL says “Incorrect table definition; there can be only one auto column and it must be defined as a key” So when I added primary key as below it started working: CREATE TABLE book ( id INT AUTO_INCREMENT NOT NULL, accepted_terms BIT(1) NOT NULL, accepted_privacy BIT(1) NOT NULL, primary key (id) ) ENGINE=InnoDB DEFAULT … Read more
You can’t. Although the SQL-92 syntax to add a foreign key to your table would be as follows: ALTER TABLE child ADD CONSTRAINT fk_child_parent FOREIGN KEY (parent_id) REFERENCES parent(id); SQLite doesn’t support the ADD CONSTRAINT variant of the ALTER TABLE command (sqlite.org: SQL Features That SQLite Does Not Implement). Therefore, the only way to add … Read more
Restrictions You can ask the system catalog pg_database – accessible from any database in the same database cluster. The tricky part is that CREATE DATABASE can only be executed as a single statement. The manual: CREATE DATABASE cannot be executed inside a transaction block. So it cannot be run directly inside a function or DO … Read more
For the record, the spring.jpa.hibernate.ddl-auto property is Spring Data JPA specific and is their way to specify a value that will eventually be passed to Hibernate under the property it knows, hibernate.hbm2ddl.auto. The values create, create-drop, validate, and update basically influence how the schema tool management will manipulate the database schema at startup. For example, … Read more
This feature has been implemented in Postgres 9.1: CREATE TABLE IF NOT EXISTS myschema.mytable (i integer); For older versions, here is a function to work around it: CREATE OR REPLACE FUNCTION create_mytable() RETURNS void LANGUAGE plpgsql AS $func$ BEGIN IF EXISTS (SELECT FROM pg_catalog.pg_tables WHERE schemaname=”myschema” AND tablename=”mytable”) THEN RAISE NOTICE ‘Table myschema.mytable already exists.’; … Read more
All commands must be executed while connected to the right database cluster. Make sure of it. Roles are objects of the database cluster. All databases of the same cluster share the set of defined roles. Privileges are granted / revoked per database / schema / table etc. A role needs access to the database, obviously. … Read more