过度规范化
回顾 loan 表的定义。
CREATE TABLE loan (
borrower_id INTEGER REFERENCES borrower(id),
bank_id INTEGER REFERENCES bank(id),
approval_date DATE NOT NULL DEFAULT CURRENT_DATE,
gross_approval DECIMAL(9, 2) NOT NULL,
term_in_months SMALLINT NOT NULL,
revolver_status BOOLEAN NOT NULL DEFAULT FALSE,
initial_interest_rate DECIMAL(4, 2) NOT NULL
);
有人建议为满足 1NF 对该表进行新的设计。修订后的表定义用 approval_month、approval_day 和 approval_year 替代了 approval_date：
CREATE TABLE loan (
...
approval_month SMALLINT,
approval_day SMALLINT,
approval_year SMALLINT,
...
);
本练习演示过度规范化如何会允许将无效数据插入到表中。
本练习是课程的一部分
创建 PostgreSQL 数据库
练习说明
- 删除那条如果执行会导致向表中插入无效数据的
INSERT INTO语句。
交互式实操练习
通过完成这段示例代码来试试这个练习。
INSERT INTO loan (
borrower_id, bank_id, approval_month, approval_day,
approval_year, gross_approval, term_in_months,
revolver_status, initial_interest_rate
) VALUES (12, 14, 12, 1, 2013, 421115, 120, false, 4.42);
INSERT INTO loan (
borrower_id, bank_id, approval_month, approval_day,
approval_year, gross_approval, term_in_months,
revolver_status, initial_interest_rate
) VALUES (3, 201, 6, 42, 2017, 30015, 60, true, 3.25);
INSERT INTO loan (
borrower_id, bank_id, approval_month, approval_day,
approval_year, gross_approval, term_in_months,
revolver_status, initial_interest_rate
) VALUES (19, 5, 8, 19, 2018, 200000, 120, false, 6.3);