SQL in 10 Minutes

《SQL 必知必会》 #

检索数据 #

检索单个列 # 

mysql> select prod_name from products;
+---------------------+
| prod_name           |
+---------------------+
| Fish bean bag toy   |
| Bird bean bag toy   |
| Rabbit bean bag toy |
| 8 inch teddy bear   |
| 12 inch teddy bear  |
| 18 inch teddy bear  |
| Raggedy Ann         |
| King doll           |
| Queen doll          |
+---------------------+
9 rows in set (0.00 sec)

检索多个列 # 

mysql> select prod_id, prod_name, prod_price
    -> from products;
+---------+---------------------+------------+
| prod_id | prod_name           | prod_price |
+---------+---------------------+------------+
| BNBG01  | Fish bean bag toy   |       3.49 |
| BNBG02  | Bird bean bag toy   |       3.49 |
| BNBG03  | Rabbit bean bag toy |       3.49 |
| BR01    | 8 inch teddy bear   |       5.99 |
| BR02    | 12 inch teddy bear  |       8.99 |
| BR03    | 18 inch teddy bear  |      11.99 |
| RGAN01  | Raggedy Ann         |       4.99 |
| RYL01   | King doll           |       9.49 |
| RYL02   | Queen doll          |       9.49 |
+---------+---------------------+------------+
9 rows in set (0.00 sec)

检索所有列 # 

mysql> select * from products;
+---------+---------+---------------------+------------+-----------------------------------------------------------------------+
| prod_id | vend_id | prod_name           | prod_price | prod_desc                                                             |
+---------+---------+---------------------+------------+-----------------------------------------------------------------------+
| BNBG01  | DLL01   | Fish bean bag toy   |       3.49 | Fish bean bag toy, complete with bean bag worms with which to feed it |
| BNBG02  | DLL01   | Bird bean bag toy   |       3.49 | Bird bean bag toy, eggs are not included                              |
| BNBG03  | DLL01   | Rabbit bean bag toy |       3.49 | Rabbit bean bag toy, comes with bean bag carrots                      |
| BR01    | BRS01   | 8 inch teddy bear   |       5.99 | 8 inch teddy bear, comes with cap and jacket                          |
| BR02    | BRS01   | 12 inch teddy bear  |       8.99 | 12 inch teddy bear, comes with cap and jacket                         |
| BR03    | BRS01   | 18 inch teddy bear  |      11.99 | 18 inch teddy bear, comes with cap and jacket                         |
| RGAN01  | DLL01   | Raggedy Ann         |       4.99 | 18 inch Raggedy Ann doll                                              |
| RYL01   | FNG01   | King doll           |       9.49 | 12 inch king doll with royal garments and crown                       |
| RYL02   | FNG01   | Queen doll          |       9.49 | 12 inch queen doll with royal garments and crown                      |
+---------+---------+---------------------+------------+-----------------------------------------------------------------------+
9 rows in set (0.00 sec)

检索不同的值 # 

mysql> select vend_id from products;
+---------+
| vend_id |
+---------+
| BRS01   |
| BRS01   |
| BRS01   |
| DLL01   |
| DLL01   |
| DLL01   |
| DLL01   |
| FNG01   |
| FNG01   |
+---------+
9 rows in set (0.00 sec)

mysql> select distinct vend_id from products;
+---------+
| vend_id |
+---------+
| BRS01   |
| DLL01   |
| FNG01   |
+---------+
3 rows in set (0.00 sec)

限制结果 # 

mysql> select prod_name from products limit 5;
+---------------------+
| prod_name           |
+---------------------+
| Fish bean bag toy   |
| Bird bean bag toy   |
| Rabbit bean bag toy |
| 8 inch teddy bear   |
| 12 inch teddy bear  |
+---------------------+
5 rows in set (0.00 sec)

mysql> select prod_name from products limit 5 offset 5;
+--------------------+
| prod_name          |
+--------------------+
| 18 inch teddy bear |
| Raggedy Ann        |
| King doll          |
| Queen doll         |
+--------------------+
4 rows in set (0.01 sec)

使用注释 # 

select prod_name     -- 这是一条注释
from products;


# 这是一条注释
select prod_name     
from products;


/* select prod_name, vend_id
   from products;
*/
select prod_name
from products;

排序检索数据 #

排序数据 # 

mysql> select prod_name from products;
+---------------------+
| prod_name           |
+---------------------+
| Fish bean bag toy   |
| Bird bean bag toy   |
| Rabbit bean bag toy |
| 8 inch teddy bear   |
| 12 inch teddy bear  |
| 18 inch teddy bear  |
| Raggedy Ann         |
| King doll           |
| Queen doll          |
+---------------------+
9 rows in set (0.00 sec)

mysql> select prod_name
    -> from products
    -> order by prod_name;
+---------------------+
| prod_name           |
+---------------------+
| 12 inch teddy bear  |
| 18 inch teddy bear  |
| 8 inch teddy bear   |
| Bird bean bag toy   |
| Fish bean bag toy   |
| King doll           |
| Queen doll          |
| Rabbit bean bag toy |
| Raggedy Ann         |
+---------------------+
9 rows in set (0.00 sec)

按多个列排序 # 

mysql> select prod_id, prod_price, prod_name
    -> from products
    -> order by prod_price, prod_name;
+---------+------------+---------------------+
| prod_id | prod_price | prod_name           |
+---------+------------+---------------------+
| BNBG02  |       3.49 | Bird bean bag toy   |
| BNBG01  |       3.49 | Fish bean bag toy   |
| BNBG03  |       3.49 | Rabbit bean bag toy |
| RGAN01  |       4.99 | Raggedy Ann         |
| BR01    |       5.99 | 8 inch teddy bear   |
| BR02    |       8.99 | 12 inch teddy bear  |
| RYL01   |       9.49 | King doll           |
| RYL02   |       9.49 | Queen doll          |
| BR03    |      11.99 | 18 inch teddy bear  |
+---------+------------+---------------------+
9 rows in set (0.00 sec)

按列位置排序 # 

mysql> select prod_id, prod_price, prod_name
    -> from products
    -> order by 2, 3;
+---------+------------+---------------------+
| prod_id | prod_price | prod_name           |
+---------+------------+---------------------+
| BNBG02  |       3.49 | Bird bean bag toy   |
| BNBG01  |       3.49 | Fish bean bag toy   |
| BNBG03  |       3.49 | Rabbit bean bag toy |
| RGAN01  |       4.99 | Raggedy Ann         |
| BR01    |       5.99 | 8 inch teddy bear   |
| BR02    |       8.99 | 12 inch teddy bear  |
| RYL01   |       9.49 | King doll           |
| RYL02   |       9.49 | Queen doll          |
| BR03    |      11.99 | 18 inch teddy bear  |
+---------+------------+---------------------+
9 rows in set (0.00 sec)

指定排序方向 # 

mysql> select prod_id, prod_price, prod_name
    -> from products
    -> order by prod_price desc;
+---------+------------+---------------------+
| prod_id | prod_price | prod_name           |
+---------+------------+---------------------+
| BR03    |      11.99 | 18 inch teddy bear  |
| RYL01   |       9.49 | King doll           |
| RYL02   |       9.49 | Queen doll          |
| BR02    |       8.99 | 12 inch teddy bear  |
| BR01    |       5.99 | 8 inch teddy bear   |
| RGAN01  |       4.99 | Raggedy Ann         |
| BNBG01  |       3.49 | Fish bean bag toy   |
| BNBG02  |       3.49 | Bird bean bag toy   |
| BNBG03  |       3.49 | Rabbit bean bag toy |
+---------+------------+---------------------+
9 rows in set (0.00 sec)

mysql> select cust_id, order_num
    -> from orders
    -> order by cust_id asc,   order_date desc;
+------------+-----------+
| cust_id    | order_num |
+------------+-----------+
| 1000000001 |     20005 |
| 1000000001 |     20009 |
| 1000000003 |     20006 |
| 1000000004 |     20007 |
| 1000000005 |     20008 |
+------------+-----------+
5 rows in set (0.01 sec)

过滤数据 #

使用where子句 # 

mysql> select prod_name, prod_price
    -> from products
    -> where prod_price = 3.49;
+---------------------+------------+
| prod_name           | prod_price |
+---------------------+------------+
| Fish bean bag toy   |       3.49 |
| Bird bean bag toy   |       3.49 |
| Rabbit bean bag toy |       3.49 |
+---------------------+------------+
3 rows in set (0.00 sec)

where 子句操作符 #

检查单个值 # 

mysql> select prod_name, prod_price
    -> from products
    -> where prod_price < 10;
+---------------------+------------+
| prod_name           | prod_price |
+---------------------+------------+
| Fish bean bag toy   |       3.49 |
| Bird bean bag toy   |       3.49 |
| Rabbit bean bag toy |       3.49 |
| 8 inch teddy bear   |       5.99 |
| 12 inch teddy bear  |       8.99 |
| Raggedy Ann         |       4.99 |
| King doll           |       9.49 |
| Queen doll          |       9.49 |
+---------------------+------------+
8 rows in set (0.00 sec)

不匹配检查 # 

mysql> select vend_id, prod_name
    -> from products
    -> where vend_id <> 'DLL01';
+---------+--------------------+
| vend_id | prod_name          |
+---------+--------------------+
| BRS01   | 8 inch teddy bear  |
| BRS01   | 12 inch teddy bear |
| BRS01   | 18 inch teddy bear |
| FNG01   | King doll          |
| FNG01   | Queen doll         |
+---------+--------------------+
5 rows in set (0.00 sec)

范围值检查 # 

mysql> select prod_name, prod_price
    -> from products
    -> where prod_price between 5 and 10;
+--------------------+------------+
| prod_name          | prod_price |
+--------------------+------------+
| 8 inch teddy bear  |       5.99 |
| 12 inch teddy bear |       8.99 |
| King doll          |       9.49 |
| Queen doll         |       9.49 |
+--------------------+------------+
4 rows in set (0.00 sec)

####空值检查

mysql> select cust_name
    -> from customers
    -> where cust_email is null;
+---------------+
| cust_name     |
+---------------+
| Kids Place    |
| The Toy Store |
+---------------+
2 rows in set (0.00 sec)

高级数据过滤 #

组合where子句 #

and 操作符 # 

mysql> select prod_id, prod_price, prod_name
    -> from products
    -> where vend_id = 'DLL01' and prod_price <= 4;
+---------+------------+---------------------+
| prod_id | prod_price | prod_name           |
+---------+------------+---------------------+
| BNBG01  |       3.49 | Fish bean bag toy   |
| BNBG02  |       3.49 | Bird bean bag toy   |
| BNBG03  |       3.49 | Rabbit bean bag toy |
+---------+------------+---------------------+
3 rows in set (0.00 sec)

or操作符 # 

mysql> select prod_name, prod_price
    -> from products
    -> where vend_id = 'DLL01' or vend_id = 'BRS01';
+---------------------+------------+
| prod_name           | prod_price |
+---------------------+------------+
| 8 inch teddy bear   |       5.99 |
| 12 inch teddy bear  |       8.99 |
| 18 inch teddy bear  |      11.99 |
| Fish bean bag toy   |       3.49 |
| Bird bean bag toy   |       3.49 |
| Rabbit bean bag toy |       3.49 |
| Raggedy Ann         |       4.99 |
+---------------------+------------+
7 rows in set (0.00 sec)

求值顺序 # 

mysql> select prod_name, prod_price
    -> from products
    -> where vend_id = 'DLL01' or vend_id = 'BRS01'
    -> and prod_price >= 10;
+---------------------+------------+
| prod_name           | prod_price |
+---------------------+------------+
| 18 inch teddy bear  |      11.99 |
| Fish bean bag toy   |       3.49 |
| Bird bean bag toy   |       3.49 |
| Rabbit bean bag toy |       3.49 |
| Raggedy Ann         |       4.99 |
+---------------------+------------+
5 rows in set (0.01 sec)

mysql> select prod_name, prod_price
    -> from products
    -> where (vend_id = 'DLL01' or vend_id = 'BRS01')
    -> and prod_price >= 10;
+--------------------+------------+
| prod_name          | prod_price |
+--------------------+------------+
| 18 inch teddy bear |      11.99 |
+--------------------+------------+
1 row in set (0.00 sec)

in 操作符 # 

mysql> select prod_name, prod_price 
    -> from products
    -> where vend_id in ('DLL011', 'BRS01')
    -> order by prod_name;
+--------------------+------------+
| prod_name          | prod_price |
+--------------------+------------+
| 12 inch teddy bear |       8.99 |
| 18 inch teddy bear |      11.99 |
| 8 inch teddy bear  |       5.99 |
+--------------------+------------+
3 rows in set (0.00 sec)

not 操作符 # 

mysql> select prod_name
    -> from products
    -> where not vend_id = 'DLL01'
    -> order by prod_name;
+--------------------+
| prod_name          |
+--------------------+
| 12 inch teddy bear |
| 18 inch teddy bear |
| 8 inch teddy bear  |
| King doll          |
| Queen doll         |
+--------------------+
5 rows in set (0.00 sec)

用通配符进行过滤 #

like 操作符 #

百分号(%)通配符 # 

mysql> select prod_id, prod_name
    -> from products
    -> where prod_name like 'Fish%';
+---------+-------------------+
| prod_id | prod_name         |
+---------+-------------------+
| BNBG01  | Fish bean bag toy |
+---------+-------------------+
1 row in set (0.00 sec)

mysql> select prod_id, prod_name
    -> from products
    -> where prod_name like '%bean bag%';
+---------+---------------------+
| prod_id | prod_name           |
+---------+---------------------+
| BNBG01  | Fish bean bag toy   |
| BNBG02  | Bird bean bag toy   |
| BNBG03  | Rabbit bean bag toy |
+---------+---------------------+
3 rows in set (0.00 sec)

mysql> select prod_name
    -> from products
    -> where prod_name like 'F%y';
+-------------------+
| prod_name         |
+-------------------+
| Fish bean bag toy |
+-------------------+
1 row in set (0.00 sec)

下划线通配符 # 

mysql> select prod_id, prod_name
    -> from products
    -> where prod_name like '__ inch teddy bear';
+---------+--------------------+
| prod_id | prod_name          |
+---------+--------------------+
| BR02    | 12 inch teddy bear |
| BR03    | 18 inch teddy bear |
+---------+--------------------+
2 rows in set (0.00 sec)

mysql> select prod_id, prod_name
    -> from products
    -> where prod_name like '% inch teddy bear';
+---------+--------------------+
| prod_id | prod_name          |
+---------+--------------------+
| BR01    | 8 inch teddy bear  |
| BR02    | 12 inch teddy bear |
| BR03    | 18 inch teddy bear |
+---------+--------------------+
3 rows in set (0.01 sec)

使用通配符的技巧 #

  • 不过度使用通配符
  • 在确实需要使用通配符时，也尽量不要把它们凡在搜索模式的开始处
  • 仔细注意通配符的位置

创建计算字段 #

计算字段 #

转换计算或格式转化的字段

拼接字段 # 

mysql> select concat(vend_name, '(', vend_country, ')') from vendors order by vend_name;
+-------------------------------------------+
| concat(vend_name, '(', vend_country, ')') |
+-------------------------------------------+
| Bear Emporium(USA)                        |
| Bears R Us(USA)                           |
| Doll House Inc.(USA)                      |
| Fun and Games(England)                    |
| Furball Inc.(USA)                         |
| Jouets et ours(France)                    |
+-------------------------------------------+
6 rows in set (0.00 sec)

mysql> select concat(rtrim(vend_name), '(', rtrim(vend_country), ')') from vendors  order by vend_name ;
+---------------------------------------------------------+
| concat(rtrim(vend_name), '(', rtrim(vend_country), ')') |
+---------------------------------------------------------+
| Bear Emporium(USA)                                      |
| Bears R Us(USA)                                         |
| Doll House Inc.(USA)                                    |
| Fun and Games(England)                                  |
| Furball Inc.(USA)                                       |
| Jouets et ours(France)                                  |
+---------------------------------------------------------+
6 rows in set (0.01 sec)

使用别名 # 

mysql> select concat(rtrim(vend_name), '(', rtrim(vend_country), ')')
    -> as vend_title
    -> from vendors
    -> order by vend_name;
+------------------------+
| vend_title             |
+------------------------+
| Bear Emporium(USA)     |
| Bears R Us(USA)        |
| Doll House Inc.(USA)   |
| Fun and Games(England) |
| Furball Inc.(USA)      |
| Jouets et ours(France) |
+------------------------+
6 rows in set (0.00 sec)

执行算术计算 # 

mysql> select prod_id, quantity, item_price
    -> from orderItems
    -> where order_num = 20008;
+---------+----------+------------+
| prod_id | quantity | item_price |
+---------+----------+------------+
| RGAN01  |        5 |       4.99 |
| BR03    |        5 |      11.99 |
| BNBG01  |       10 |       3.49 |
| BNBG02  |       10 |       3.49 |
| BNBG03  |       10 |       3.49 |
+---------+----------+------------+
5 rows in set (0.00 sec)

mysql> select prod_id,
    -> quantity,
    -> item_price,
    -> quantity*item_price as expanded_price
    -> from orderItems
    -> where order_num = 20008;
+---------+----------+------------+----------------+
| prod_id | quantity | item_price | expanded_price |
+---------+----------+------------+----------------+
| RGAN01  |        5 |       4.99 |          24.95 |
| BR03    |        5 |      11.99 |          59.95 |
| BNBG01  |       10 |       3.49 |          34.90 |
| BNBG02  |       10 |       3.49 |          34.90 |
| BNBG03  |       10 |       3.49 |          34.90 |
+---------+----------+------------+----------------+
5 rows in set (0.00 sec)

使用函数处理数据 #

函数带来的问题 #

可移植性差

使用函数 #

文本处理函数 # 

mysql> select vend_name, upper(vend_name) as vend_name_upcase                       -> from vendors
    -> order by vend_name;
+-----------------+------------------+
| vend_name       | vend_name_upcase |
+-----------------+------------------+
| Bear Emporium   | BEAR EMPORIUM    |
| Bears R Us      | BEARS R US       |
| Doll House Inc. | DOLL HOUSE INC.  |
| Fun and Games   | FUN AND GAMES    |
| Furball Inc.    | FURBALL INC.     |
| Jouets et ours  | JOUETS ET OURS   |
+-----------------+------------------+
6 rows in set (0.00 sec)

mysql> select cust_name, cust_contact
    -> from customers
    -> where soundex(cust_contact)=soundex('Michael Green');
+------------+----------------+
| cust_name  | cust_contact   |
+------------+----------------+
| Kids Place | Michelle Green |
+------------+----------------+
1 row in set (0.01 sec)

日期和时间处理函数 # 

mysql> select order_num
    -> from orders
    -> where year(order_date) = 2020;
+-----------+
| order_num |
+-----------+
|     20005 |
|     20006 |
|     20007 |
|     20008 |
|     20009 |
+-----------+
5 rows in set (0.01 sec)

mysql>  select cust_id, cust_name,
    -> upper(concat(substring(cust_contact, 1, 2), substring(cust_city, 1, 3)))
    -> as user_login
    -> from customers;
+------------+---------------+------------+
| cust_id    | cust_name     | user_login |
+------------+---------------+------------+
| 1000000001 | Village Toys  | JODET      |
| 1000000002 | Kids Place    | MICOL      |
| 1000000003 | Fun4All       | JIMUN      |
| 1000000004 | Fun4All       | DEPHO      |
| 1000000005 | The Toy Store | KICHI      |
+------------+---------------+------------+
5 rows in set (0.00 sec)



mysql> select order_num, order_date
    -> from orders
    -> where year(order_date) = 2020
    -> and month(order_date) = 1
    -> order by order_date desc;
    +-----------+---------------------+
    | order_num | order_date          |
    +-----------+---------------------+
    |     20007 | 2020-01-30 00:00:00 |
    |     20006 | 2020-01-12 00:00:00 |
    +-----------+---------------------+
    2 rows in set (0.01 sec)

汇总数据 #

聚集函数 #

  • AVG()
  • COUNT()
  • MAX()
  • MIN()
  • SUM()

AVG函数 # 

mysql> select avg(prod_price) as avg_price
    -> from products;
+-----------+
| avg_price |
+-----------+
|  6.823333 |
+-----------+
1 row in set (0.01 sec)


mysql> select avg(prod_price) as avg_price
    -> from products
    -> where vend_id = 'DLL01';
+-----------+
| avg_price |
+-----------+
|  3.865000 |
+-----------+
1 row in set (0.01 sec)

COUNT函数 #

  • count(*)包含null
  • count(column)忽略null
mysql> select count(*) as num_cust
    -> from customers;
+----------+
| num_cust |
+----------+
|        5 |
+----------+
1 row in set (0.01 sec)

mysql> select count(cust_email)_custum 
    -> from customers;
+----------+
| num_cust |
+----------+
|        3 |
+----------+
1 row in set (0.00 sec)

MAX()函数 # 


mysql> select max(prod_price) as max_price 
    -> from products;
+-----------+
| max_price |
+-----------+
|     11.99 |
+-----------+
1 row in set (0.00 sec)

MIN()函数 # 

mysql> select min(prod_price) as min_price
    -> from products;
+-----------+
| min_price |
+-----------+
|      3.49 |
+-----------+
1 row in set (0.00 sec)

SUM()函数 # 

mysql> select sum(quantity) as items_ordered 
    -> from orderItems
    -> where order_num = 20005;
+---------------+
| items_ordered |
+---------------+
|           200 |
+---------------+
1 row in set (0.01 sec)

mysql> select sum(item_price*quantity) as total_price
    -> from orderItems
    -> where order_num = 20005;
+-------------+
| total_price |
+-------------+
|     1648.00 |
+-------------+
1 row in set (0.00 sec)

聚集不同值 # 

mysql> select avg(distinct prod_price) as avg_price
    -> from products
    -> where vend_id='DLL01';
+-----------+
| avg_price |
+-----------+
|  4.240000 |
+-----------+
1 row in set (0.01 sec)

组合聚集函数 # 

mysql> select count(*) as num_items,
    -> min(prod_price) as price_min,
    -> max(prod_price) as price_max,
    -> avg(prod_price) as price_avg
    -> from products;
+-----------+-----------+-----------+-----------+
| num_items | price_min | price_max | price_avg |
+-----------+-----------+-----------+-----------+
|         9 |      3.49 |     11.99 |  6.823333 |
+-----------+-----------+-----------+-----------+
1 row in set (0.00 sec)

mysql> select max(prod_price) 
    -> from products
    -> where prod_price < 10;
+-----------------+
| max(prod_price) |
+-----------------+
|            9.49 |
+-----------------+
1 row in set (0.00 sec)

分组数据 #

数据分组 # 

mysql> select count(*) as num_prods from products
    -> where vend_id = 'Dll01';
+-----------+
| num_prods |
+-----------+
|         4 |
+-----------+
1 row in set (0.01 sec)

创建分组 # 

mysql> select vend_id, count(*) as num_prods
    -> from products
    -> group by vend_id;
+---------+-----------+
| vend_id | num_prods |
+---------+-----------+
| BRS01   |         3 |
| DLL01   |         4 |
| FNG01   |         2 |
+---------+-----------+
3 rows in set (0.01 sec)

过滤分组 # 

mysql> select cust_id, count(*) as orders
    -> from orders
    -> group by cust_id
    -> having count(*) >=2;
+------------+--------+
| cust_id    | orders |
+------------+--------+
| 1000000001 |      2 |
+------------+--------+
1 row in set (0.00 sec)


mysql> select vend_id, count(*) as num_prods
           -> from products
           -> where prod_price >= 4
           -> group by vend_id
           -> having count(*) >= 2;
+---------+-----------+
| vend_id | num_prods |
+---------+-----------+
| BRS01   |         3 |
| FNG01   |         2 |
+---------+-----------+
2 rows in set (0.00 sec)

where 是进入group by前的过滤条件 having 是 group 之后的过滤条件

分组和排序 # 

mysql> select order_num, count(*) as items
    -> from orderItems
    -> group by order_num
    -> having count(*) >= 3;
+-----------+-------+
| order_num | items |
+-----------+-------+
|     20006 |     3 |
|     20007 |     5 |
|     20008 |     5 |
|     20009 |     3 |
+-----------+-------+
4 rows in set (0.01 sec)

mysql> select order_num, count(*) as items
           -> from orderItems
           -> group by order_num
           -> having count(*) >= 3
           -> order by items, order_num;
+-----------+-------+
| order_num | items |
+-----------+-------+
|     20006 |     3 |
|     20009 |     3 |
|     20007 |     5 |
|     20008 |     5 |
+-----------+-------+
4 rows in set (0.01 sec)

使用子查询 #

子查询 #

嵌套在其他查询中的查询

利用子查询进行过滤 # 


mysql> select order_num 
    -> from orderItems
    -> where prod_id = 'RGAN01';
+-----------+
| order_num |
+-----------+
|     20007 |
|     20008 |
+-----------+
2 rows in set (0.00 sec)

mysql> select cust_id
    -> from orders
    -> where order_num in (20007, 20008);
+------------+
| cust_id    |
+------------+
| 1000000004 |
| 1000000005 |
+------------+
2 rows in set (0.00 sec)

mysql> select cust_id
    -> from orders
    -> where order_num in (select order_num
    -> from orderItems
    -> where prod_id = 'RGAN01');
+------------+
| cust_id    |
+------------+
| 1000000004 |
| 1000000005 |
+------------+
2 rows in set (0.00 sec)

mysql> select cust_name, cust_contact
    -> from customers
    -> where cust_id in (1000000004, 1000000005);
+---------------+--------------------+
| cust_name     | cust_contact       |
+---------------+--------------------+
| Fun4All       | Denise L. Stephens |
| The Toy Store | Kim Howard         |
+---------------+--------------------+
2 rows in set (0.00 sec)

mysql> select cust_name, cust_contact
    -> from customers
    -> where cust_id in (select cust_id from orders
    -> where order_num in (select order_num
    -> from orderItems
    -> where prod_id = 'RGAN01'));
+---------------+--------------------+
| cust_name     | cust_contact       |
+---------------+--------------------+
| Fun4All       | Denise L. Stephens |
| The Toy Store | Kim Howard         |
+---------------+--------------------+
2 rows in set (0.00 sec)

子查询只能是单列

作为计算字段使用子查询 # 

mysql> select cust_name,
    -> cust_state,
    -> (select count(*) from orders
    -> where orders.cust_id = customers.cust_id) as orders
    -> from customers
    -> order by cust_name;
+---------------+------------+--------+
| cust_name     | cust_state | orders |
+---------------+------------+--------+
| Fun4All       | IN         |      1 |
| Fun4All       | AZ         |      1 |
| Kids Place    | OH         |      0 |
| The Toy Store | IL         |      1 |
| Village Toys  | MI         |      2 |
+---------------+------------+--------+
5 rows in set (0.01 sec)

mysql> select cust_name, order_num from customers, orders where orders.cust_id = customers.cust_id;

mysql> select cust_name, order_num from customers, orders where customers.cust_id = orders.cust_id;

小结 #

子查询常用于where 子句的 in 操作符中，以及用来填充计算列

联结表 #

创建联结 # 

mysql> select vend_name, prod_name, prod_price
    -> from vendors, products
    -> where vendors.vend_id = products.vend_id;
+-----------------+---------------------+------------+
| vend_name       | prod_name           | prod_price |
+-----------------+---------------------+------------+
| Doll House Inc. | Fish bean bag toy   |       3.49 |
| Doll House Inc. | Bird bean bag toy   |       3.49 |
| Doll House Inc. | Rabbit bean bag toy |       3.49 |
| Bears R Us      | 8 inch teddy bear   |       5.99 |
| Bears R Us      | 12 inch teddy bear  |       8.99 |
| Bears R Us      | 18 inch teddy bear  |      11.99 |
| Doll House Inc. | Raggedy Ann         |       4.99 |
| Fun and Games   | King doll           |       9.49 |
| Fun and Games   | Queen doll          |       9.49 |
+-----------------+---------------------+------------+
9 rows in set (0.00 sec)

内联结 # 

mysql> select vend_name, prod_name, prod_price
    -> from vendors
    -> inner join products on vendors.vend_id = products.vend_id;
+-----------------+---------------------+------------+
| vend_name       | prod_name           | prod_price |
+-----------------+---------------------+------------+
| Doll House Inc. | Fish bean bag toy   |       3.49 |
| Doll House Inc. | Bird bean bag toy   |       3.49 |
| Doll House Inc. | Rabbit bean bag toy |       3.49 |
| Bears R Us      | 8 inch teddy bear   |       5.99 |
| Bears R Us      | 12 inch teddy bear  |       8.99 |
| Bears R Us      | 18 inch teddy bear  |      11.99 |
| Doll House Inc. | Raggedy Ann         |       4.99 |
| Fun and Games   | King doll           |       9.49 |
| Fun and Games   | Queen doll          |       9.49 |
+-----------------+---------------------+------------+
9 rows in set (0.00 sec)

联结多个表 # 

mysql> select prod_name, vend_name, prod_price, quantity
    -> from orderItems, products, vendors
    -> where products.vend_id = vendors.vend_id
    -> and orderItems.prod_id = products.prod_id
    -> and order_num = 20007;
+---------------------+-----------------+------------+----------+
| prod_name           | vend_name       | prod_price | quantity |
+---------------------+-----------------+------------+----------+
| 18 inch teddy bear  | Bears R Us      |      11.99 |       50 |
| Fish bean bag toy   | Doll House Inc. |       3.49 |      100 |
| Bird bean bag toy   | Doll House Inc. |       3.49 |      100 |
| Rabbit bean bag toy | Doll House Inc. |       3.49 |      100 |
| Raggedy Ann         | Doll House Inc. |       4.99 |       50 |
+---------------------+-----------------+------------+----------+
5 rows in set (0.00 sec)


mysql> select cust_name, cust_contact
    -> from customers
    -> where cust_id in
    -> (select cust_id
    -> from orders where order_num in
    -> (select order_num
    -> from orderItems
    -> where prod_id = 'RGAN01'));
+---------------+--------------------+
| cust_name     | cust_contact       |
+---------------+--------------------+
| Fun4All       | Denise L. Stephens |
| The Toy Store | Kim Howard         |
+---------------+--------------------+
2 rows in set (0.00 sec)

ysql> select cust_name, cust_contact
    -> from customers, orders, orderItems
    -> where customers.cust_id = orders.cust_id
    -> and orderItems.order_num = orders.order_num
    -> and prod_id = 'RGAN01';
+---------------+--------------------+
| cust_name     | cust_contact       |
+---------------+--------------------+
| Fun4All       | Denise L. Stephens |
| The Toy Store | Kim Howard         |
+---------------+--------------------+
2 rows in set (0.01 sec)

资源 #