列表 6. 单个事务中的串行查询

CREATE TABLE Salaries (
    person_id      INT4         NOT NULL  REFERENCES People,
    monthly_gross  NUMERIC(8,0) NOT NULL  CHECK (monthly_gross > 0),
    as_of          DATE         NOT NULL,
    approved_by    INT4         NOT NULL  REFERENCES People,
    notes          VARCHAR(255) NULL,

    UNIQUE(person_id, as_of)
);