CREATE TABLE packages ( id INT GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY. If the column fails either of those checks, the alter table command will fail. Tables inheriting entities table will get the column along with the constraints. 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. 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. Add new column Modify column Rename column Rename and modify column Drop column Add unique key Drop unique key Add index Drop index Add foreign key. 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. 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". \d usersĪs you can see we currently have one constraint, which is asserting that the employee number is unique. ALTER TABLE mytable ADD COLUMN mycolumn character varying (50) NOT NULL DEFAULT foo. We can also inspect the table to see the current columns and constraints. 8 Answers Sorted by: 509 You have to set a default value. 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.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |