一、簡單查詢:
基本語法:
查詢全部
代碼如下 復制代碼 SELECT field1,field2 FROM tb_name;投影
代碼如下 復制代碼 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
如下查詢本博客的wp-links和wp_posts表:
代碼如下 復制代碼mysql> select * from wp_links; 查詢全部 mysql> select link_name,link_url from wp_links; 投影
+-------------------+--------------------------------------+
| link_name | link_url |
+-------------------+--------------------------------------+
| 旺旺騰訊微博 | http://www.111cn.net |
| 旺旺新浪微博 | http://weibo.com/gz100ww |
| 51CTO技術博客 | http://www.111cn.net/ |
+-------------------+--------------------------------------+
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創建虛擬機報錯 | 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常用命令、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語句之常用管理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}
如下:
##升序,ID是排序的字段
代碼如下 復制代碼 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 … :對表使用別名
如下:
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創建虛擬機報錯 |
| linux下強大的網絡工具Netcat |
| MySQL常用命令、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語句之常用管理SQL |
+----------------------------------------------------------------+
7 rows in set (0.02 sec)
##還可以這樣:
代碼如下 復制代碼mysql> select 3+2 AS SUM;
+-----+
| SUM |
+-----+
| 5 |
+-----+
1 row in set (0.00 sec)
LIMIT子句:LIMIT [offset,]Count
如下:
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創建虛擬機報錯 | 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常用命令、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' limit 2,3; ##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創建虛擬機報錯 | 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常用命令、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
分組:GROUP BY,一般配合聚合運算使用
如下:
mysql> select count(post_status) AS 各狀態數量,post_status AS 狀態名稱 from wp_posts group by post_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 qualification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
外連接:
左外連接:left_tb LEFT JOIN right_tb ON ... :以左表為標准
右外連接 : left_tb RIGHT JOIN right_tb ON ... :以右表為標准
代碼如下 復制代碼 mysql> SELECT s.Name,c.Cname FROM students AS s RIGHT JOIN courses AS c ON s.CID1=c.CID;自連接:本表中不同字段間進行連接
代碼如下 復制代碼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表中查詢年齡大於平均年齡的學生
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並