sql - 如何使用Postgres添加指向2个表之一的外键？

Question

我想添加一个外键，用于检查记录或个人记录表之一中是否存在事件的记录 ID。可以用 Postgres 做吗？

CREATE TABLE record
(
    id BIGSERIAL PRIMARY KEY
);

CREATE TABLE personal_record
(
    id BIGSERIAL PRIMARY KEY
);

CREATE TABLE activity
(
    id        BIGSERIAL PRIMARY KEY,
    record_id BIGINT NOT NULL,
    CONSTRAINT record_fk FOREIGN KEY (record_id) REFERENCES record (id)
);

Answer 1

如前所述，这是不可能的。一种可能性是生成的列和可为空的引用:

CREATE TABLE activity (
    id BIGINT GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
    private_record_id BIGINT,
    private_personal_record_id BIGINT,
    record_id BIGINT GENERATED ALWAYS AS (COLAESCE(private_record_id, private_personal_record_id)),
    CHECK( (private_record_id IS NOT NULL AND private_personal_record_id IS NULL) OR
           (private_record_id IS NULL AND private_personal_record_id IS NOT NULL)
         ),           
    CONSTRAINT fk_activity_record_id FOREIGN KEY (private_record_id) REFERENCES record(id),
    CONSTRAINT fk_activity_record_id FOREIGN KEY (private_personal_record_id) REFERENCES personal_record(id),
);

您可能还想研究继承。