本來想總結高可用叢集的另外幾個實驗呢，回頭看看别人總結的内容，好精細，而且擴充了好多内容，慚愧的不行，還是先跳過了，呵呵~~~
介紹了簡單的資料庫操作等，接下來從細節入手，來介紹mysql的查詢語句；
在這裡導入了一個jiaowu資料庫，來實作以下例題的操作：
先來看下這個資料庫所包含的内容
mysql>show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| jiaowu |
| mysql |
| test |
+--------------------+
4 rows in set (0.00 sec)
l> use jiaowu;
Database changed
mysql>show tables;
+------------------+
| Tables_in_jiaowu |
+------------------+
| courses |
| scores |
| students |
| tutors |
+------------------+
4 rows in set (0.00 sec)mysql>select * from students;
+-----+--------------+------+--------+------+------+------+---------------------+
| SID | Name | Age | Gender | CID1 | CID2 | TID | CreateTime |
+-----+--------------+------+--------+------+------+------+---------------------+
| 1 | GuoJing | 19 | M | 2 | 7 | 3 | 2012-04-06 10:00:00 |
| 2 | YangGuo | 17 | M | 2 | 3 | 1 | 2012-04-06 10:00:00 |
| 3 | DingDian | 25 | M | 6 | 1 | 7 | 2012-04-06 10:00:00 |
| 4 | HuFei | 31 | M | 8 | 10 | 5 | 2012-04-06 10:00:00 |
| 5 | HuangRong | 16 | F | 5 | 9 | 9 | 2012-04-06 10:00:00 |
| 6 | YueLingshang | 18 | F | 8 | 4 | NULL | 2012-04-06 10:00:00 |
| 7 | ZhangWuji | 20 | M | 1 | 7 | NULL | 2012-04-06 10:00:00 |
| 8 | Xuzhu | 26 | M | 2 | 4 | NULL | 2012-04-06 10:00:00 |
| 9 | LingHuchong | 22 | M | 11 | NULL | NULL | 2012-04-06 10:00:00 |
| 10 | YiLin | 19 | F | 18 | NULL | NULL | 2012-04-06 10:00:00 |
+-----+--------------+------+--------+------+------+------+---------------------+
10 rows in set (0.00 sec)mysql>select * from tutors;
+-----+--------------+--------+------+
| TID | Tname | Gender | Age |
+-----+--------------+--------+------+
| 1 2 | HuangYaoshi | M | 63 |
| 3 | Miejueshitai | F | 72 |
| 4 | OuYangfeng | M | 76 |
| 5 | YiDeng | M | 90 |
| 6 | YuCanghai | M | 56 |
| 7 | Jinlunfawang | M | 67 |
| 8 | HuYidao | M | 42 |
| 9 | NingZhongze | F | 49 |
+-----+--------------+--------+------+
9 rows in set (0.00 sec)
這是以下例題中會用到的資料，可以先參考下；
首先是mysql查詢語句：
查詢的分類：
單表查詢：簡單查詢
多表查詢：聯結查詢
子查詢：複雜查詢
聯合查詢
select語句：
常用函數：
##field--表示字段
count(*) 總行數
mysql>select count(*) from tutors;
+----------+
| count(*) |
+----------+
| 9 |
+---------+
1 row in set (0.00 sec)
max(field) 傳回最大值
mysql>select max(age) from tutors;
+----------+
| max(age) |
+----------+
| 93 |
+----------+
1 row in set (0.00 sec)
min(field) 傳回最小值
avg(field) 平均值
mysql>select avg(age) from tutors;
+----------+
| avg(age) |
+----------+
| 67.5556 |
+----------+
1 row in set (0.00 sec)
sum() 記和
mysql>select sum(1+2);
+----------+
| sum(1+2) |
+----------+
| 3 |
+----------+
1 row in set (0.01 sec)
select 是挑選列的，where是挑選行的，二者結合起來才是将一個實體的屬性整體顯示出來
where 後面指定的是條件：
可以指定的條件有：
算術比較：
> , < , = , ！,>= , <=, <=> (取得的結果是空值也不會出錯)
mysql>select name,age from students where age>=20;
+-------------+------+
| name | age |
+-------------+------+
| DingDian | 25 |
| HuFei | 31 |
| ZhangWuji | 20 |
| Xuzhu | 26 |
| LingHuchong | 22 |
+-------------+------+
5 rows in set (0.00 sec)
組合邏輯比較：
and
or
not(!)
mysql>select name,age from students where ! (age<=25);
+-------+------+
| name | age |
+-------+------+
| HuFei | 31 |
| Xuzhu | 26 |
+-------+------+
2 rows in set (0.00 sec)
其他條件比較：
beween …… and ……
mysql>select name,age from students where age between 24 and 30
+----------+------+
| name | age |
+----------+------+
| DingDian | 25 |
| Xuzhu | 26 |
+----------+------+
2 rows in set (0.00 sec)
in 查詢的字段在指定的清單中
mysql>select name,age from students where age in (18,20,25);
+--------------+------+
| name | age |
+--------------+------+
| DingDian | 25 |
| YueLingshang | 18 |
| ZhangWuji | 20 |
+--------------+------+
3 rows in set (0.01 sec)
is null：查詢是空值的
mysql>select name from students where cid2 is null;
+-------------+
| name |
+-------------+
| LingHuchong |
| YiLin |
+-------------+
2 rows in set (0.00 sec)
is not null
like : 做通配符的比對
%：比對任意長度的任意字元
_: 比對單個字元
regexp|rlike : 正規表達式的比對
order by: 排序，預設是升序的asc
desc：降序
mysql>select name,age from students where age in (22,18,25)order by age desc;
+--------------+------+
| name | age |
+--------------+------+
| DingDian | 25 |
| LingHuchong | 22 |
| YueLingshang | 18 |
+--------------+------+
3 rows in set (0.00 sec)
distinct: 顯示結果的唯一性，附在select之後(以下面的例子解說，cid1相同的隻顯示了一次)
mysql>select distinct cid1 from students order by cid1 desc;
+------+
| cid1 |
+------+
| 18 |
| 11 |
| 8 |
| 6 |
| 5 |
| 2 |
| 1 |
+------+
7 rows in set (0.00 sec)
group by: 将取得的結果進行分組，通常分組的結果是用來做聚合運算的
having: 對分組的結果進行條件過濾
mysql>select avg(age),cid1 from students group by cid1;
+----------+------+
| avg(age) | cid1 |
+----------+------+
| 20.0000 | 1 |
| 20.6667 | 2 |
| 16.0000 | 5 |
| 25.0000 | 6 |
| 24.5000 | 8 |
| 22.0000 | 11 |
| 19.0000 | 18 |
+----------+------+
7 rows in set (0.00 sec)
limit：限定顯示的行數
eg：limit 1,2;表示跳過第一行再顯示兩行
mysql>select avg(age),cid1 from students group by cid1 limit 1,2;
+----------+------+
| avg(age) | cid1 |
+----------+------+
| 20.6667 | 2 |
| 16.0000 | 5 |
+----------+------+
2 rows in set (0.00 sec)
