Question

I’ve got three tables: A, B and C. I want to create table A, and it should have 3 columns, first one should be a PRIMARY KEY.

1) How to create second column, with is a refference to table B,

2) and third with is a refference to ‘C.id’ row from table C. A.id = C.id

CREATE TABLE A
(
    id SERIAL PRIMARY KEY,
    // ? - reference to table B
    // ? - reference to C.id row. A.id = C.id
)

Database: postgresql

Answer 1

I assume you use mysql database.

CREATE TABLE A
(
    id INT NOT NULL PRIMARY KEY,
    b_id INT NOT NULL,
    c_id INT NOT NULL,
    FOREIGN KEY (b_id) REFERENCES B (id),
    FOREIGN KEY (c_id) REFERENCES C (id)
) TYPE = INNODB;

Update for using postgresql:

CREATE TABLE "A"
(
   id integer NOT NULL, 
   b_id integer NOT NULL, 
   c_id integer NOT NULL, 
   CONSTRAINT id PRIMARY KEY (id), 
   CONSTRAINT b_id FOREIGN KEY (b_id) REFERENCES "B" (id) 
      ON UPDATE NO ACTION ON DELETE NO ACTION, --with no action restriction
   CONSTRAINT c_id FOREIGN KEY (c_id) REFERENCES "C" (id) 
      ON UPDATE CASCADE ON DELETE CASCADE  --with cascade restriction
) 
WITH (
  OIDS = FALSE
)
;
ALTER TABLE "C" OWNER TO postgres;

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