MySQL基本SQL語句之單表查詢、多表查詢和子查詢

本文首發自我的博客：http://www.toxingwang.com/database/mysql/1402.html

1、簡單查詢：

基本語法：

SELECT * FROM tb_name;查詢所有

SELECT field1,field2 FROM tb_name; 投影

SELECT [DISTINCT] * FROM tb_name WHERE qualification; 選擇

說明：

FROM子句： 要查詢的關係 表、多個表、其它SELECT語句

WHERE子句：布爾關係表達式，主要包含以下這幾類表達式：

比較：=、>、>=、<=、<
邏輯關係：
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

以下查詢本博客的wp-links和wp_posts表：

mysql> select * from wp_links; 查詢所有 mysql> select link_name,link_url from wp_links; 投影
+-------------------+--------------------------------------+
| link_name | link_url |
+-------------------+--------------------------------------+
| 旺旺騰訊微博 | http://t.qq.com/toxingwang |
| 旺旺新浪微博 | http://weibo.com/gz100ww |
| 51CTO技術博客 | http://towangwang.blog.51cto.com/ |
+-------------------+--------------------------------------+
10 rows in set (0.00 sec)

mysql> select ID,post_title,post_date from wp_posts where ID>1290 and post_status='publish';選擇
+------+----------------------------------------------------------------+----------------------+
| ID | post_title | post_date |
+------+----------------------------------------------------------------+----------------------+
| 1291 | 【轉】HP 3PAR存儲概念之三 | 2013-08-29 17:21:27 |
| 1298 | 【轉】HP 3PAR存儲概念之四 | 2013-08-29 17:22:33 |
| 1351 | 【轉】XenDesktop 5.5+vSphere 5建立虛擬機報錯 | 2013-09-04 17:41:26 |
| 1357 | linux下強大的網絡工具Netcat | 2013-09-09 22:26:45 |
| 1360 | MySQL經常使用命令、技巧和注意事項 | 2013-09-20 11:04:15 |
| 1369 | 【轉】數據庫設計原理知識--B樹、B-樹、B+樹、B*樹都是什麼 | 2013-09-21 12:30:18 |
| 1379 | MySQL基本SQL語句之經常使用管理SQL | 2013-09-21 12:39:23 |
+------+----------------------------------------------------------------+---------------------+
7 rows in set (0.01 sec)

對查詢結果排序：

ORDER BY field_name {ASC|DESC}

以下：

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

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 … ：對錶使用別名

以下：

mysql> select post_title AS 文章標題 from wp_posts where ID>1290 and post_status='publish';
+----------------------------------------------------------------+
| 文章標題 |
+----------------------------------------------------------------+
| 【轉】HP 3PAR存儲概念之三 |
| 【轉】HP 3PAR存儲概念之四 |
| 【轉】XenDesktop 5.5+vSphere 5建立虛擬機報錯 |
| linux下強大的網絡工具Netcat |
| MySQL經常使用命令、技巧和注意事項 |
| 【轉】數據庫設計原理知識--B樹、B-樹、B+樹、B*樹都是什麼 |
| MySQL基本SQL語句之經常使用管理SQL |
+----------------------------------------------------------------+
7 rows in set (0.02 sec)

##還能夠這樣:

mysql> select 3+2 AS SUM;
+-----+
| SUM |
+-----+
| 5 |
+-----+
1 row in set (0.00 sec)

LIMIT子句：LIMIT [offset,]Count

以下：

mysql> select ID,post_title,post_date from wp_posts where ID>1290 and post_status='publish' limit 5;
+------+--------------------------------------------------+---------------------+
| ID | post_title | post_date |
+------+--------------------------------------------------+---------------------+
| 1291 | 【轉】HP 3PAR存儲概念之三 | 2013-08-29 17:21:27 |
| 1298 | 【轉】HP 3PAR存儲概念之四 | 2013-08-29 17:22:33 |
| 1351 | 【轉】XenDesktop 5.5+vSphere 5建立虛擬機報錯 | 2013-09-04 17:41:26 |
| 1357 | linux下強大的網絡工具Netcat | 2013-09-09 22:26:45 |
| 1360 | MySQL經常使用命令、技巧和注意事項 | 2013-09-20 11:04:15 |
+------+--------------------------------------------------+---------------------+
5 rows in set (0.01 sec)

mysql> select ID,post_title,post_date from wp_posts where ID>1290 and post_status='publish' limit2,3; ##紅色部分（逗號前的數字）表示偏移量
+------+--------------------------------------------------+---------------------+
| ID | post_title | post_date |
+------+--------------------------------------------------+---------------------+
| 1351 | 【轉】XenDesktop 5.5+vSphere 5建立虛擬機報錯 | 2013-09-04 17:41:26 |
| 1357 | linux下強大的網絡工具Netcat | 2013-09-09 22:26:45 |
| 1360 | MySQL經常使用命令、技巧和注意事項 | 2013-09-20 11:04:15 |
+------+--------------------------------------------------+---------------------+
3 rows in set (0.00 sec)

聚合：SUM(), MIN(), MAX(), AVG(), COUNT()，括號中爲字段名

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

分組：GROUP BY，通常配合聚合運算使用

以下：

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：能夠使用HAVING qualification將GROUP BY的結果再次過濾，用法同where

2、多表查詢

鏈接：

交叉鏈接：笛卡爾乘積
天然鏈接：將兩張表某字段中相等鏈接起來，以下

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)

外鏈接：
左外鏈接：left_tb LEFT JOIN right_tb ON ... ：以左表爲標準

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)

右外鏈接 : left_tb RIGHT JOIN right_tb ON ... ：以右表爲標準

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)

自鏈接：本表中不一樣字段間進行鏈接

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

3、子查詢：一個查詢中嵌套另一個查詢

以下：在students表中查詢年齡大於平均年齡的學生

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：

• 比較操做中使用子查詢：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併

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)