MySQL

1、選擇數據庫

use dbname

show databases;

2、數據表

show tables

mysql> show columns from customers;

mysql> desc customers;

3、show 語句

show status

show create databases

show create table

show grants

4、select 檢索

4.1.1版本后不再區分大小寫，但是為了容易閱讀和調試，建議還是使用。

mysql> select cust_name from customers; mysql> select cust_name cust_status from customers; mysql> select distinct vend_id from products; mysql> select prod_name from products limit 5; mysql> select prod_name from products limit 5,5; //分頁問題 從行0開始計數，limit5,5是從第5行開始（不包括第五行），取5行，結果是：6:10行 因為這個很容易引起誤解，所以MySQL5開始支持另一個語法：limit 4 offset 3，意思是從行3開始取4行，等同于limit 3,4

4-1、排序數據

//單個字段排序 mysql> select prod_name from products order by prod_name; //多個字段排序，如果第一個字段全部唯一則第二個字段就不會生效 mysql> select prod_id,prod_price,prod_name from products order by prod_price ,prod_name;

4-2、指定排序方向

• desc 降序
• asc 升序-默認

注意順序，from>ordrr by >limit

mysql> select prod_id,prod_price,prod_name from products order by prod_price desc; mysql> select prod_id,prod_price,prod_name from products order by prod_price asc; mysql> select prod_price from products order by prod_price desc limit 1;

5、where 條件

相關操作符：

= 等于

<> 不等于

!= 不等于

< 小于

> 大于

>= 大于或者等于

<= 小于或等于

between 兩者之間 and

and 的優先級大于or，需要處理or，則需要括號 mysql> select prod_price,prod_name from products where prod_price = 2.50; mysql> select prod_price,prod_name from products where prod_price between 5 and 10; // IS NULL mysql> select cust_id from customers where cust_email is null; 重點：空值檢查
空值既是：NULL
MySQL中判斷是否是空值的子句是： IS NULL

example:

mysql> select cust_id FROM customers where cust_email IS NULL; +---------+ | cust_id | +---------+ | 10002 | | 10005 | +---------+

6、where 數據過濾

（logical operator）邏輯操作符：and - or

mysql> select prod_id,prod_price,prod_name from products where vend_id = 1003 and prod_price<= 10; mysql> select prod_id,prod_price,prod_name from products where vend_id = 1003 or vend_id = 1002;

運算符優先級問題：
下列SQL中實際先運行 vend_id = 1002 and prod_price >= 10;,再運行vend_id = 1003.因為and的優先級大于or，如果要按理想執行，加括號！

mysql> select prod_id,prod_price,prod_name from products where vend_id = 1003 or vend_id = 1002 and prod_price >= 10; mysql> select prod_id,prod_price,prod_name from products where (vend_id = 1003 or vend_id = 1002 )and prod_price >= 10;

6-1、 in操作符 (not in)

mysql> select prod_id,prod_price,prod_name from products where vend_id in (1002,1003) order by prod_name;

6-2、 or操作符

mysql> select prod_id,prod_price,prod_name from products where vend_id not in (1002,1003) order by prod_name;

7、用通配符過濾

like 和 _ 的區別是后者只能匹配一個字符

7-1、like

**注意NULL 雖然似乎 % 通配符可以匹配任何東西，但有一個例
外，即 NULL 。即使是 WHERE prod_name LIKE '%' 也不能匹配
用值 NULL 作為產品名的行。**

mysql> select prod_id,prod_price,prod_name from products where prod_name LIKE 'jet%';mysql> select prod_id,prod_price,prod_name from products where prod_name LIKE '%anv%';

7-2、_

mysql> select prod_id,prod_price,prod_name from products where prod_name LIKE '_ ton anvil';

8、正則表達式

like是匹配全部，REGEXP可以匹配全部和部分

mysql> select prod_name from products where prod_name ='JetPack 1000'; +--------------+ | prod_name | +--------------+ | JetPack 1000 | +--------------+ 1 row in set (0.00 sec)mysql> select prod_name from products where prod_name REGEXP '1000'; +--------------+ | prod_name | +--------------+ | JetPack 1000 | +--------------+ 1 row in set (0.00 sec)

默認不區分大小寫，需要區分大小寫binary

mysql> select prod_name from products where prod_name REGEXP 'jetpack .000'; mysql> select prod_name from products where prod_name REGEXP binary 'JetPack .000';

10、計算字段

concat 合并 講兩個字段合并成一個新的字段

mysql> select concat (vend_name , 'C',vend_country,')') from vendors order by vend_name; +-------------------------------------------+ | concat (vend_name , 'C',vend_country,')') | +-------------------------------------------+ | ACMECUSA) | | Anvils R UsCUSA) | | Furball Inc.CUSA) | | Jet SetCEngland) | | Jouets Et OursCFrance) | | LT SuppliesCUSA) | +-------------------------------------------+ 6 rows in set (0.00 sec)

rtrim (ltrim ,trim) 去掉空格

mysql> select concat (rtrim(vend_name) , 'C',vend_country,')') from vendors order by vend_name;

as 別名

mysql> select concat (rtrim(vend_name) , '(',rtrim(vend_country),')') as vend_title from vendors order by vend__name;

計算

+、-、* 、\

mysql> select quantity*item_price as expand_price from orderitems where order_num =20005;

11、函數

trim、ltrim、rtrim 去掉空值

Upper 轉為大寫

mysql> select vend_name,upper(vend_name) as ven_name_upcase from vendors order by vend_name;

11-2 時間函數

AddDate() 增加一個日期(天、周等)

AddTime() 增加一個時間(時、分等)

CurDate() 返回當前日期

CurTime() 返回當前時間

==Date() 返回日期時間的日期部分==

DateDiff() 計算兩個日期之差

Date_Add() 高度靈活的日期運算函數

Date_Format() 返回一個格式化的日期或時間串

Day() 返回一個日期的天數部分

DayOfWeek() 對于一個日期，返回對應的星期幾

Hour() 返回一個時間的小時部分

Minute() 返回一個時間的分鐘部分

Month() 返回一個日期的月份部分

Now() 返回當前日期和時間

Second() 返回一個時間的秒部分

Time() 返回一個日期時間的時間部分

Year() 返回一個日期的年份部分

取9月某一天的數據

mysql> select cust_id,order_num from orders where Date(order_date) = '2005-09-01'; +---------+-----------+ | cust_id | order_num | +---------+-----------+ | 10001 | 20005 | +---------+-----------+ 1 row in set (0.00 sec)

取9月整個月的訂單

mysql> select cust_id,order_num from orders where Date(order_date) between '2005-09-01' and '2005-09-30'; +---------+-----------+ | cust_id | order_num | +---------+-----------+ | 10001 | 20005 | | 10003 | 20006 | | 10004 | 20007 | +---------+-----------+ 3 rows in set (0.00 sec)mysql> select cust_id,order_num from orders where Year(order_date) and month(order_date) = 9; +---------+-----------+ | cust_id | order_num | +---------+-----------+ | 10001 | 20005 | | 10003 | 20006 | | 10004 | 20007 | +---------+-----------+ 3 rows in set (0.00 sec)

11-4 數值處理函數

Abs() 返回一個數的絕對值

Cos() 返回一個角度的余弦

Exp() 返回一個數的指數值

Mod() 返回除操作的余數

Pi() 返回圓周率

Rand() 返回一個隨機數

Sin() 返回一個角度的正弦

Sqrt() 返回一個數的平方根

Tan() 返回一個角度的正切

11-5 聚集函數

AVG() 返回某列的平均值

COUNT() 返回某列的行數

MAX() 返回某列的最大值

MIN() 返回某列的最小值

SUM() 返回某列值之和

DISTINCT

mysql> select avg(prod_price) as avg_price from products;

分組數據

GROUP BY子句和HAVING子句

mysql> select vend_id,count(*) as num_prods from products group by vend_id; +---------+-----------+ | vend_id | num_prods | +---------+-----------+ | 1001 | 3 | | 1002 | 2 | | 1003 | 7 | | 1005 | 2 | +---------+-----------+ 4 rows in set (0.00 sec)mysql> select vend_id,count(*) as num_prods from products group by vend_id with rollup; +---------+-----------+ | vend_id | num_prods | +---------+-----------+ | 1001 | 3 | | 1002 | 2 | | 1003 | 7 | | 1005 | 2 | | NULL | 14 | +---------+-----------+ 5 rows in set (0.00 sec) having
唯一的差別是 WHERE過濾行，而HAVING過濾分組。WHERE在數據 分組前進行過濾，HAVING在數據分組后進行過濾 mysql> select vend_id,count(*) as num_prods from products group by vend_id having count(*)>=2; +---------+-----------+ | vend_id | num_prods | +---------+-----------+ | 1001 | 3 | | 1002 | 2 | | 1003 | 7 | | 1005 | 2 | +---------+-----------+ 4 rows in set (0.00 sec)mysql> select vend_id,count(*) as num_prods from products where prod_price>=10 group by vend_id having count(*)>=2; +---------+-----------+ | vend_id | num_prods | +---------+-----------+ | 1003 | 4 | | 1005 | 2 | +---------+-----------+ 2 rows in set (0.00 sec)mysql> select order_num ,sum(quantity*item_price) as ordertotal from orderitems -> group by order_num -> having sum(quantity*item_price) >= 50 -> order by ordertotal; +-----------+------------+ | order_num | ordertotal | +-----------+------------+ | 20006 | 55.00 | | 20008 | 125.00 | | 20005 | 149.87 | | 20007 | 1000.00 | +-----------+------------+ 4 rows in set (0.00 sec) 順序

• select
• from
• where
• group by
• having
• order by
• limit

12 子查詢

mysql> select cust_id from orders where order_num in (select order_num from orderitems where prod_id ='TNT2'); +---------+ | cust_id | +---------+ | 10001 | | 10004 | +---------+

15 連接表

笛卡兒積(cartesian product)

如果將兩個表同時作為數據源(from后的表名)，不加任何的匹配條件，那么產生的結果集就是一個迪卡爾積。
迪卡爾積的結果沒有意義，但是迪卡爾積是聯合查詢、連接查詢的基礎。

1. 交叉連接 cross join

使用表A中的1條記錄去表B中連接所有的記錄，就是笛卡爾積

2. 內連接

select 字段列表 from 表A 【inner】 join 表B ，匹配到的成功的記錄

3. 外連接 分為左連接和右連接，

左連接保留左邊的所有，右邊匹配到的部分

4. using關鍵字

在進行連接時，如果進行連接的兩個字段的名子相同，則可以使用using using('cid') 當前筆記出自 《MySQL必知必會》

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