作业：
1.创建一个表products
| 字段名 | 数据类型 | 含义 |
|---|---|---|
| product_id | INTEGER | 产品编号 |
| product_name | Char(30) | 产品名 |
| category | Char(20) | 种类 |
omm=# create table products ( product_id integer,product_name char(30),caregory char(20));
CREATE TABLE
2.向表中插入数据，采用一次插入一条和多条记录的方式
| product_id | product_name | category |
|---|---|---|
| 1502 | olympus camera | electrncs |
| 1601 | lamaze | toys |
| 1700 | wait interface | Books |
| 1666 | harry potter | toys |
单条插入
omm=# insert into products (product_id,product_name,caregory) values (1502,'olympus camera','electrncs');
INSERT 0 1
多条插入
omm=# insert into products values (1601,'lamaze','toys'),(1700,'wait interface','Books'),(1666,'harry potter','toys');
INSERT 0 3
3.查询表中所有记录及记录数
omm=# select * from products;
product_id | product_name | caregory
------------+--------------------------------+----------------------
1502 | olympus camera | electrncs
1601 | lamaze | toys
1700 | wait interface | Books
1666 | harry potter | toys
(4 rows)
4.查询表中所有category记录，并将查询结果按升序排序
omm=# select caregory from products order by caregory;
caregory
----------------------
Books
electrncs
toys
toys
(4 rows)
5.查询表中category为toys的记录
omm=# select * from products where caregory='toys';
product_id | product_name | caregory
------------+--------------------------------+----------------------
1601 | lamaze | toys
1666 | harry potter | toys
(2 rows)
6.删除表products
omm=# drop table products;
omm=# DROP TABLE
