SQL 基础教程 SQL语句集

nowgood

环境 PostgreSQL 9.6.4
终端 字符集编码 \'gbk\'

chapter01 数据库和 SQL


sudo chown -R postgres PostgreSQL

sudo -u postgres psql -U postgres
create database shop;
\encoding \'gbk\'

\q

sudo -u psql -U postgres -d shop

psql -U user -d dbname

\c dbname
\l
\dt
\d tblname
\di

sql 中

  1. 等于号是 =, 而不是 ==;
  2. 单行注释为 --, 多行注释 /**/;
  3. 语句结束符为 , 

create table Product (
  product_id char(4)  not null,
  product_name varchar(20) not null,
  product_type varchar(20) not null,
  sale_price integer,
  purchase_price integer,
  register_date date,
  primary key(product_id)
);

drop table Product;

alter table Product add column sales integer;
alter table Product drop column sales;

show client_encoding;
set client_encoding to \'gbk\'
set client_encoding to \'utf8\'

begin transaction;

INSERT INTO Product VALUES (\'0001\', \'T恤\' ,\'衣服\', 1000, 500, \'2009-09-20\');
INSERT INTO Product VALUES (\'0002\', \'打孔器\', \'办公用品\', 500, 320, \'2009-09-11\');
INSERT INTO Product VALUES (\'0003\', \'运动T恤\', \'衣服\', 4000, 2800, NULL);
INSERT INTO Product VALUES (\'0004\', \'菜刀\', \'厨房用具\', 3000, 2800, \'2009-09-20\');
INSERT INTO Product VALUES (\'0005\', \'高压锅\', \'厨房用具\', 6800, 5000, \'2009-01-15\');
INSERT INTO Product VALUES (\'0006\', \'叉子\', \'厨房用具\', 500, NULL, \'2009-09-20\');
INSERT INTO Product VALUES (\'0007\', \'擦菜板\', \'厨房用具\', 880, 790, \'2008-04-28\');
INSERT INTO Product VALUES (\'0008\', \'圆珠笔\', \'办公用品\', 100, NULL, \'2009-11-11\');

commit;


sudo -u postgres pg_ctl -D /usr/local/PostgreSQL/9.6/data/ -w start
sudo -u postgres pg_ctl -D /usr/local/PostgreSQL/9.6/data/ -w restart
sudo -u postgres pg_ctl -D /usr/local/PostgreSQL/9.6/data/ -w stop

exercise


create table Addressbook (
  regist_no integer primary key,
  name varchar(128) not null,
  address varchar(256) not null,
  tel_no char(10),
  mail_address char(20)
);

alter table Addressbook add column postal_code char(8) not null;
drop table Addressbook;

chapter02 查询基础

2.1

select product_id, product_name, product_type from Product;

-- 查询结果中列的顺序和 select 子句中的顺序相同
select product_type, product_id, product_name from Product;

select * from Product;

select product_id as id, product_name as name, product_type as type from Product;

-- 别名可以使用中文,  使用中文需要双引号括起来
select product_id as "商品编号", product_name as "商品名称", product_type as "商品类型" from Product;

-- select 子句不仅能书写列名, 还可以书写常数
select \'商品\' as String, 66 as number, \'2017-08-20\' as date, product_id from Product;

-- distinct 关键字只能用在第一个关键字前, 将 select 子句的所有字段联合起来判断相等性
select distinct product_type, register_date from product

-- 首先通过 where 子句查询出符合条件的记录, 然后使用 select 子句指定列
select product_name, product_type from product where product_type = \'衣服\';
-- 查询条件可以不显示出来
select product_name from product where product_type = \'衣服\';

2.2

-- 注意要起个别名, 因为之前的字段名字不可用
select sale_price * 2  as double_price from product;

-- 所有包含 null 的计算, 结果肯定是 null
select sale_price * null  as multi_null from product;

-- <> 不等号
select product_name, sale_price from product where sale_price <> 500;

select product_name, sale_price, purchase_price from Product where sale_price - purchase_price >= 500;

-- 不能对 null 使用比较运算符, 不管怎么用, 查询结果都为空; SQL 专门用来判断是否为null的是 is null 运算符
select product_name, purchase_price from product where purchase_price is null;
select product_name, purchase_price from product where purchase_price is not null;

2.3

逻辑运算符 not, and, or

  1. and 运算符的优先级高于 or 运算符
  2. 善用括号()
select product_name, purchase_price, sale_price from product where sale_price >= 500;
select product_name, purchase_price, sale_price from product where not sale_price >= 500;

select product_name, product_type, register_date from Product
where product_type = \'办公用品\' and register_date = \'2009-09-11\' or register_date = \'2009-09-20\';

select product_name, product_type, register_date from Product
where product_type = \'办公用品\' and (register_date = \'2009-09-11\' or register_date = \'2009-09-20\');

SQL 中逻辑运算时三值逻辑, 真值除了真假之外还有 unknown, 关于 unknown 运算如下

P Q P AND Q
真 unknown unknown
假 unknown 假
unknown unknown unknown
P Q P OR Q
真 unknown 真
假 unknown unknown
unknown unknown unknown

可以看出了 unknown 是一种介于真假之间的逻辑状态

exercise

select product_name, register_date from product where register_date >\'2009-04-28\';

-- SELECT语句①
SELECT product_name, sale_price, purchase_price
  FROM Product
 WHERE sale_price >= purchase_price + 500;


-- SELECT语句②
SELECT product_name, sale_price, purchase_price
  FROM Product
 WHERE sale_price - 500 >= purchase_price;

select product_name, product_type, (sale_price * 0.9 - purchase_price) as profit from product
where sale_price * 0.9 - purchase_price  > 100 and (product_type = \'办公用品\' or product_type = \'厨房用具\');

chapter03 聚合和排序

3.1

聚合函数中使用 distinct, 删除重复数据

-- count(*) 会得到包含 null 的数据行数, count(<列名>) 会得到 null 之外的数据行数
select count(*) from Product;
select count(*) from Product where product_type = \'衣服\';
select count(distinct product_type) from Product;


select count(purchase_price) from Product;

select sum(sale_price), sum(purchase_price) from Product;
select sum(sale_price), sum(distinct sale_price) from Product;

select avg(sale_price), avg(purchase_price) from Product;

select max(register_date), min(register_date) from product;

3.2

group by 子句的书写位置

select -> from -> where -> group by

上述语句的执行顺序

from -> where -> group by -> select

select product_type, count(product_type) from Product group by product_type;

-- group by 可以包含 null 的分组
select purchase_price, count(*) from Product group by purchase_price;

-- 有 where 子句, 先根据 where 子句指定的条件进行过滤, 然后再进行汇总处理
select purchase_price, count(*) from Product where product_type = \'衣服\' group by purchase_price;

3.3

having 子句必须写在 group by 子句之后, 执行顺序也在 group by 之后

书写规范

  • where 子句 = 指定行所对应的条件
  • having 子句 = 指定组所对应的条件

select product_type, count(*) from Product group by product_type having count(*) = 2;

3.4

order by 子句书写顺序在 having 之后, 排序时, 默认为升序

ascendent adj 递增的
descendent adj 递减的

DBMS 中, 语句执行顺序

from -> where -> group by -> having -> select -> order by


select * from Product order by sale_price;
select * from Product order by sale_price desc, product_id;

-- 排序键包含 null, 会在开头或者末尾汇总

chapter04 数据更新

4.1


CREATE TABLE ProductIns
(product_id      CHAR(4)      NOT NULL,
 product_name    VARCHAR(100) NOT NULL,
 product_type    VARCHAR(32)  NOT NULL,
 sale_price      INTEGER      DEFAULT 0,
 purchase_price  INTEGER      ,
 regist_date     DATE         ,
 PRIMARY KEY (product_id));

-- 单条记录插入
insert into ProductIns (product_id, product_name, product_type, sale_price, purchase_price, regist_date) values (\'0001\', \'T恤\' ,\'衣服\', 1000, 500, \'2009-09-20\');

-- 多条记录插入, 记录间用逗号隔开, 语句结尾用分号结束
insert into ProductIns (product_id, product_name, product_type, sale_price, purchase_price, regist_date) values
  (\'0002\', \'打孔器\', \'办公用品\', 500, 320, \'2009-09-11\'),
  (\'0003\', \'运动T恤\', \'衣服\', 4000, 2800, NULL),
  (\'0004\', \'菜刀\', \'厨房用具\', 3000, 2800, \'2009-09-20\'),
  (\'0005\', \'高压锅\', \'厨房用具\', 6800, 5000, \'2009-01-15\'),
  (\'0006\', \'叉子\', \'厨房用具\', 500, NULL, \'2009-09-20\'),
  (\'0007\', \'擦菜板\', \'厨房用具\', 880, 790, \'2008-04-28\');

-- 对表进行全列插入时, 可以省略列清单
insert into ProductIns values (\'0008\', \'圆珠笔\', \'办公用品\', 100, NULL, \'2009-11-11\');

-- default 使用默认值
insert into ProductIns values (\'0009\', \'圆珠笔\', \'办公用品\', default, NULL, \'2009-11-11\');


-- 从其他表复制数据 insert ... select ...
create table ProductCopy (
  product_id char(4)  not null,
  product_name varchar(20) not null,
  product_type varchar(20) not null,
  sale_price integer,
  purchase_price integer,
  register_date date,
  primary key(product_id)
);

insert into ProductCopy (product_id, product_name, product_type, sale_price, purchase_price, register_date)
select * from product;

create table productType (
  product_type varchar(32) not null,
  sum_sale_price integer,
  sum_purchase_price integer,
  primary key (product_type)
);

/*
insert ... select 中的 select 子句可以前面学到的是任意select 查询语句
同样对表进行全列插入时, 可以省略 列清单
*/
insert into productType
select product_type, sum(sale_price), sum(purchase_price) from product group by product_type;

select * from producttype;

4.2

delete 语句删除对象不是表或者列, 而是记录.


delete from ProductCopy;
insert into ProductCopy (product_id, product_name, product_type, sale_price, purchase_price, register_date)

delete from ProductCopy where sale_price >= 4000;
truncate ProductType;

-- 删除列
alter table ProductCopy drop column register_date;
alter table ProductCopy add column register_date date;

update ProductCopy set register_date = \'2017-08-19\';
update ProductCopy set sale_price = sale_price * 10 where product_type = \'厨房用具\';
update ProductCopy set register_date = null where product_id = \'0008\';

-- 多列更新
update Productcopy set sale_price = sale_price / 10, purchase_price = purchase_price + 99 where product_type = \'厨房用具\';

4-4

事务

ACID: 原子性, 一致性, 隔离性, 持久性


begin transaction;
update ProductCopy set register_date = \'2016-08-19\';
commit;

begin transaction;
update ProductCopy set register_date = \'3016-08-19\';
rollback;

exercise


create table ProductMargin (
  product_id char(4) not null,
  product_name varchar(100) not null,
  sale_price integer,
  purchase_price integer,
  margin integer,
  primary key (product_id)
);

insert into ProductMargin (product_id, product_name, sale_price, purchase_price, margin)
  select product_id, product_name, sale_price, purchase_price, sale_price - purchase_price from ProductCopy;

update ProductMargin set sale_price = sale_price + 200 where product_name = \'擦菜板\';
update ProductMargin set margin = sale_price - purchase_price where product_name = \'擦菜板\';

chapter05 复杂查询

5.1 视图

create view ProductSum (product_type, count_product)
  AS select product_type, count(product_type) from product group by product_type;

-- 多重视图
create view ProductSumJim (product_type, count_product)
 AS
 select * from ProductSum where product_type = \'办公用品\';

-- cascade 串联
drop view ProductSum cascade;

5.2 子查询

create view ProductSum (product_type, count_product)
  AS select product_type, count(*) from product group by product_type;

select product_type, count_product from ProductSum;

-- 等价于
select product_type, count_product from (select product_type, count(*) as count_product from product group by product_type) as ProductSum1;

-- 标量子查询
select product_name, product_type, sale_price from product where sale_price > (select avg(sale_price) from Product);

select product_name, product_type, sale_price, (select avg(sale_price) from Product) from product;

-- 关联子查询 (group by product_type) 可省略
select product_name, product_type, sale_price from product as p1 where sale_price >
(select avg(sale_price) from Product as p2 where p1.product_type = p2.product_type group by product_type);

exercise


create view ViewExer5_1 (product_name, sale_price, register_date)
  AS select product_name, sale_price, register_date from Product where sale_price >= 1000 and register_date = \'2009-09-20\';
select * from ViewExer5_1;

insert into ViewExer5_1 values (\'刀子\', 300, \'2009-11-02\');
/*
ERROR:  null value in column "product_id" violates not-null constraint
DETAIL:  Failing row contains (null, 刀子, null, 300, null, 2009-11-02).
*/

select product_id, product_name, product_type, sale_price, (select avg(sale_price) from product) as sale_price_all from Product;

select product_id, product_name, product_type, sale_price, (
  select avg(sale_price) from product as p2 where p1.product_type = p2.product_type
) as sale_price_all
from Product as p1;

chapter06 函数 谓词 case 表达式

5.1 函数

select current_date, current_time, current_timestamp;

select current_timestamp,
extract(year from current_timestamp) as year,
extract(month from current_timestamp) as month,
extract(day from current_timestamp) as day,
extract(hour from current_timestamp) as hour,
extract(minute from current_timestamp) as minute,
extract(second from current_timestamp) as second;

5.2谓词

CREATE TABLE ShopProduct
(shop_id    CHAR(4)       NOT NULL,
 shop_name  VARCHAR(200)  NOT NULL,
 product_id CHAR(4)       NOT NULL,
 quantity   INTEGER       NOT NULL,
 PRIMARY KEY (shop_id, product_id));

 --MySQL
 START TRANSACTION;

 INSERT INTO ShopProduct (shop_id, shop_name, product_id, quantity) VALUES (\'000A\',	\'东京\',		\'0001\',	30);
 INSERT INTO ShopProduct (shop_id, shop_name, product_id, quantity) VALUES (\'000A\',	\'东京\',		\'0002\',	50);
 INSERT INTO ShopProduct (shop_id, shop_name, product_id, quantity) VALUES (\'000A\',	\'东京\',		\'0003\',	15);
 INSERT INTO ShopProduct (shop_id, shop_name, product_id, quantity) VALUES (\'000B\',	\'名古屋\',	\'0002\',	30);
 INSERT INTO ShopProduct (shop_id, shop_name, product_id, quantity) VALUES (\'000B\',	\'名古屋\',	\'0003\',	120);
 INSERT INTO ShopProduct (shop_id, shop_name, product_id, quantity) VALUES (\'000B\',	\'名古屋\',	\'0004\',	20);
 INSERT INTO ShopProduct (shop_id, shop_name, product_id, quantity) VALUES (\'000B\',	\'名古屋\',	\'0006\',	10);
 INSERT INTO ShopProduct (shop_id, shop_name, product_id, quantity) VALUES (\'000B\',	\'名古屋\',	\'0007\',	40);
 INSERT INTO ShopProduct (shop_id, shop_name, product_id, quantity) VALUES (\'000C\',	\'大阪\',		\'0003\',	20);
 INSERT INTO ShopProduct (shop_id, shop_name, product_id, quantity) VALUES (\'000C\',	\'大阪\',		\'0004\',	50);
 INSERT INTO ShopProduct (shop_id, shop_name, product_id, quantity) VALUES (\'000C\',	\'大阪\',		\'0006\',	90);
 INSERT INTO ShopProduct (shop_id, shop_name, product_id, quantity) VALUES (\'000C\',	\'大阪\',		\'0007\',	70);
 INSERT INTO ShopProduct (shop_id, shop_name, product_id, quantity) VALUES (\'000D\',	\'福冈\',		\'0001\',	100);

COMMIT;

select * from shopproduct;  

select  product_name, sale_price from product as p
where exists (select * from shopproduct as sp where shop_id = \'000C\' and p.product_id =   sp.product_id);

5.3 case 表达式


-- 使用简单CASE表达式的情况
SELECT product_name,
       CASE product_type
            WHEN \'衣服\'    THEN \'A：\' || product_type
            WHEN \'办公用品\' THEN \'B：\' || product_type
            WHEN \'厨房用具\' THEN \'C：\' || product_type
            ELSE NULL
        END AS abc_product_type
  FROM Product;



--List6-A
--使用查询CASE表达式的情况（代码清单6-41再刊）
SELECT product_name,
       CASE WHEN product_type = \'衣服\'    THEN \'A：\' || product_type
            WHEN product_type = \'办公用品\' THEN \'B：\' || product_type
            WHEN product_type = \'厨房用具\' THEN \'C：\' || product_type
            ELSE NULL
       END AS abc_product_type
  FROM Product;

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