PostgreSQL adds various constraint syntax

Turn from PostgreSQL to add various constraint syntaxes

1. Add a PRIMARY key

ALTER TABLE goods add primary key (SID);

2. Add a foreign key

ALTER TABLE orders add foreign key (goods_id) references goods (SID) on the update cascade on DELETE cascade;

On UPDATE cascade: The referenced row is updated automatically when the referenced row is updated;

On update restrict: The referenced row is prohibited from being updated;

On DELETE cascade: When the referenced row is deleted, the reference row is also deleted;

On dellete restrict: The referenced row is forbidden to delete;

3. Delete foreign keys

ALTER TABLE orders drop constraint Orders_goods_id_fkey;

4. Add a UNIQUE constraint

ALTER TABLE goods add constraint Unique_goods_sid unique (SID);

5. Delete default values

ALTER TABLE goods ALTER COLUMN SID drop default;

6. Modifying the data type of a field

ALTER TABLE goods ALTER COLUMN SID type character varying;

7. Renaming fields

ALTER TABLE goods rename column SID to SSID;

PostgreSQL adds various constraint syntax