一、簡單查詢：

1.基本語法：

SELECT * FROM tb_name;//查詢全部

SELECT field1,field2 FROM tb_name; //投影

SELECT [DISTINCT] * FROM tb_name WHERE qualification; //選擇

說明：

FROM子句： 要查詢的關系 表、多個表、其它SELECT語句

WHERE子句：布爾關系表達式，主要包含如下這幾類表達式：

比較：=、>、>=、<=、<

邏輯關系：

AND

OR

NOT

BETWEEN ... AND ... ：在兩個值之間

LIKE ‘’

%: 任意長度任意字符

_：任意單個字符

REGEXP, RLIKE :正則表達式，此時索引無效

IN

IS NULL

IS NOT NULL

2.對查詢結果排序：

ORDER BY ?field_name {ASC|DESC}

實例：

mysql> select ID,post_title,post_date from wp_posts where ID>1290 and post_status='publish' ORDER by ID; //升序,ID是排序的字段

mysql> select ID,post_title,post_date from wp_posts where ID>1290 and post_status='publish' ORDER by ID DESC;//降序

3.字段別名：AS

select col_name AS COL_Aliases … //對字段使用別名

select col_name,… from tb_name AS tb_Aliases … //對表使用別名

4.LIMIT子句：

mysql> select ID,post_title,post_date from wp_posts where ID>1290 and post_status='publish' limit 5;//顯示匹配到的5條數據

mysql> select ID,post_title,post_date from wp_posts where ID>1290 and post_status='publish' limit2,3; //(逗號前的數字)表示偏移量

5.聚合：SUM(), MIN(), MAX(), AVG(), COUNT()，括號中為字段名

mysql> select sum(ID) from wp_posts;//計算和

mysql> select min(ID) from wp_posts;//查早最小的

mysql> select max(ID) from wp_posts; //查找最大的

mysql> select avg(ID) from wp_posts; //平均值

mysql> select count(ID) from wp_posts;//計數

6.分組：GROUP BY，一般配合聚合運算使用

mysql> select count(post_status) AS 各狀態數量,post_status AS 狀態名稱 from wp_posts group bypost_status;

+-----------------+--------------+

| 各狀態數量 | 狀態名稱 |

+-----------------+--------------+

| 1 | auto-draft |

| 9 | draft |

| 251 | inherit |

| 238 | publish |

| 2 | trash |

+-----------------+--------------+

5 rows in set (0.01 sec)

注意：可以使用HAVING ?將GROUP BY的結果再次過濾，用法同where

二、多表查詢

連接：

交叉連接：笛卡爾乘積

自然連接：將兩張表某字段中相等連接起來，如下

mysql> SELECT students.Name,students.Age,courses.Cname,students.Gender FROM students,courses WHERE students.CID1 = courses.CID;

+--------------+------+------------------+--------+

| Name | Age | Cname | Gender |

+--------------+------+------------------+--------+

| GuoJing | 19 | TaiJiquan | M |

| YangGuo | 17 | TaiJiquan | M |

| DingDian | 25 | Qishangquan | M |

| HuFei | 31 | Wanliduxing | M |

| HuangRong | 16 | Qianzhuwandushou | F |

| YueLingshang | 18 | Wanliduxing | F |

| ZhangWuji | 20 | Hamagong | M |

| Xuzhu | 26 | TaiJiquan | M |

+--------------+------+------------------+--------+

8 rows in set (0.00 sec)

外連接：

左外連接：left_tbLEFT JOINright_tb ON ... ：以左表為標準

mysql> SELECT s.Name,c.Cname FROM students AS s LEFT JOIN courses AS c ON s.CID1=c.CID;

+--------------+--------------------+

| Name | Cname |

+--------------+--------------------+

| GuoJing | TaiJiquan |

| YangGuo | TaiJiquan |

| DingDian | Qishangquan |

| HuFei | Wanliduxing |

| HuangRong | Qianzhuwandushou |

| YueLingshang | Wanliduxing |

| ZhangWuji | Hamagong |

| Xuzhu | TaiJiquan |

| LingHuchong | NULL |

| YiLin | NULL |

+--------------+--------------------+

10 rows in set (0.00 sec)

右外連接 : left_tb RIGHT JOIN right_tb ON ... ：以右表為標準

mysql> SELECT s.Name,c.Cname FROM students AS s RIGHT JOIN courses AS c ON s.CID1=c.CID;

+--------------+--------------------+

| Name | Cname |

+--------------+--------------------+

| GuoJing | TaiJiquan |

| YangGuo | TaiJiquan |

| DingDian | Qishangquan |

| HuFei | Wanliduxing |

| HuangRong | Qianzhuwandushou |

| YueLingshang | Wanliduxing |

| ZhangWuji | Hamagong |

| Xuzhu | TaiJiquan |

| NULL | Yiyangzhi |

| NULL | Jinshejianfa |

| NULL | Qiankundanuoyi |

| NULL | Pixiejianfa |

| NULL | Jiuyinbaiguzhua |

+--------------+--------------------+

13 rows in set (0.01 sec)

自連接：本表中不同字段間進行連接

mysql> SELECT c.Name AS student,s.Name AS teacher FROM students AS c,students AS s WHERE c.TID=s.SID;

+-----------+-------------+

| student | teacher |

+-----------+-------------+

| GuoJing | DingDian |

| YangGuo | GuoJing |

| DingDian | ZhangWuji |

| HuFei | HuangRong |

| HuangRong | LingHuchong |

+-----------+-------------+

5 rows in set (0.02 sec)

注意：使用了別名

三、子查詢：一個查詢中嵌套另外一個查詢

如下：在students表中查詢年齡大于平均年齡的學生

mysql> SELECT Name,Age FROM students WHERE Age > (SELECT AVG(Age) FROM students);

+-------------+------+

| Name | Age |

+-------------+------+

| DingDian | 25 |

| HuFei | 31 |

| Xuzhu | 26 |

| LingHuchong | 22 |

+-------------+------+

4 rows in set (0.08 sec)

子查詢注意事項：

比較操作中使用子查詢：子查詢只能返回單個值；

IN(): 使用子查詢；

在FROM中使用子查詢；

聯合查詢：UNION,將兩個查詢的結果合并

mysql> (SELECT Name,Age FROM students) UNION (SELECT Tname,Age FROM tutors);

+--------------+------+

| Name | Age |

+--------------+------+

| GuoJing | 19 |

| YangGuo | 17 |

| DingDian | 25 |

| HuFei | 31 |

| HuangRong | 16 |

| YueLingshang | 18 |

| ZhangWuji | 20 |

| HuYidao | 42 |

| NingZhongze | 49 |

+--------------+------+

19 rows in set (0.00 sec)

總結

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