数据库习题求 更正，数据库入门好难啊

苦逼管理研究生自学和数据库写完发现没有答案，特来，请大家帮我看看有没有问题 最后一问不清楚需求请求说明一下！

(a)CREATE TABLE customer (
        cust_id      CHAR(5),
cust_name   VARCHAR(20) NOT NULL,
Phone       CHAR(11),
Email       TEXT,
        PRIMARY KEY (cust_id));

CREATE TABLE magazine (
        mag_id      CHAR(5),
mag_name,   VARCHAR(20) NOT NULL,
unit_price_grey,  NUMERIC(3,2),
unit_price_colour NUMERIC(3,2),
        PRIMARY KEY ( mag_id ));

CREATE TABLE advert (
        ad_id       CHAR(5),
cust_id      CHAR(5) ,
ad_name    VARCHAR(20) NOT NULL,
category    TEXT,
Height      NUMERIC(20,2),
Width      NUMERIC(20,2),
is_colour    TEXT CHECK(true,false),
PRIMARY KEY(ad_id),
FOREIGN KEY (cust_id) REFERENCES customer);


CREATE TABLE placement(
        ad_id      CHAR(5),
mag_id     VARCHAR(20) UNIQUE,
date       TEXT,
        PRIMARY KEY ( ad_id, mag_id,)
FOREIGN KEY (ad_id) REFERENCES advert
FOREIGN KEY (mag_id) REFERENCES magazine);

(b)(i)SELECT mag_name , unit_price_grey
FROM magazine
ORDER BY unit_price_grey DESC;

(ii)SELECT c.cust_name 
FROM customer c
JOIN adverse a
     ON a.cust_id=c.cust_id
WHERE category =’Food’
ORDER BY cust_name ASC;

(iii)SELECT category,tot(ad_id)
FROM adverse a
JOIN place p
     ON p.ad_id=a.ad_id
Where date = ‘2022-04-%’
ORDER BY tot(ad_id) DESC;

(c)STEP1 ALTER TABLE placement RENAME TO placement_TMP;
.tables 
COMPANY_TMP  TESTBAK
 
STEP2 CREATE TABLE placement(
        ad_id      CHAR(5),
mag_id     VARCHAR(20) NOT NULL ,
date       TEXT,
amount     TEXT DEFAULT(1),
        PRIMARY KEY ( ad_id, mag_id,)
FOREIGN KEY (ad_id) REFERENCES advert
FOREIGN KEY (mag_id) REFERENCES magazine);

STEP3  INSERT INTO COMPANY(ad_id, mag_id, date) 
SELECT ad_id, mag_id, date
FROM placement_TMP;
DROP TABLE placement_TMP;
.tables
placement  TESTBAK

(d)

(d)

题目意思翻译一下，大概要实现什么。创建表、插入数据。。。