postgres 3

CREATE TABLE products (
    product_no integer,
    name text,
    price numeric DEFAULT 9.99
);

CREATE TABLE products (
    product_no integer  PRIMARY KEY ,
    name text UNIQUE,
    price numeric CHECK (price > 0),
    discounted_price numeric NOT NULL,
    CHECK (discounted_price > 0 AND price > discounted_price)
);

CREATE TABLE t1 (
  a integer PRIMARY KEY,
  b integer,
  c integer,
  FOREIGN KEY (b, c) REFERENCES other_table (c1, c2)
);

CREATE TABLE products (
    product_no integer PRIMARY KEY,
    name text,
    price numeric
);

CREATE TABLE orders (
    order_id integer PRIMARY KEY,
    shipping_address text,
    ...
);

CREATE TABLE order_items (
    product_no integer REFERENCES products ON DELETE RESTRICT, --SET NULL and SET DEFAULT
    order_id integer REFERENCES orders ON DELETE CASCADE,
    quantity integer,
    PRIMARY KEY (product_no, order_id)
);

ALTER TABLE products ADD COLUMN description text;

ALTER TABLE products DROP COLUMN description CASCADE;

ALTER TABLE products ADD CHECK (name <> '');
ALTER TABLE products ADD CONSTRAINT some_name UNIQUE (product_no);
ALTER TABLE products ADD FOREIGN KEY (product_group_id) REFERENCES product_groups;
ALTER TABLE products ALTER COLUMN product_no SET NOT NULL;

ALTER TABLE products DROP CONSTRAINT some_name;

ALTER TABLE products ALTER COLUMN price SET DEFAULT 7.77;
ALTER TABLE products ALTER COLUMN price DROP DEFAULT;
ALTER TABLE products ALTER COLUMN price TYPE numeric(10,2);
ALTER TABLE products RENAME COLUMN product_no TO product_number;
ALTER TABLE products RENAME TO items;