MySQL入門很簡單——讀書筆記
阿新 • • 發佈：2019-01-17
第八章 檢視
試圖是從一個或多個表中匯出來的表，是一種虛擬存在的表。檢視就像一個視窗，通過這個視窗，可以看到系統專門提供的資料。這樣，使用者可以只看到對自己有用的資料，而不用看到整個資料表中的其他資料。
8.1檢視簡介
8.1.1 檢視是一種虛擬的表，是從資料庫中一個或多個表中匯出來的表。檢視還可以從已經存在的檢視的基礎上定義。
資料庫中只存在了檢視的定義，而並沒有存放檢視中的資料。使用檢視進行查詢時，資料庫系統會從原來的表中取出對應的資料。
檢視是在原有的表或者檢視的基礎上重新定義的虛擬表，這可以從原有的表上選取對使用者有用的資訊。那些對使用者沒用，或者使用者沒有許可權去了解的資訊，都可以直接遮蔽掉。
這樣既使應用簡單化，也保證了系統的安全。
檢視的作用：
1.使操作簡單化：檢視需要達到的目的是所見即所需。從試圖看到的資訊就是所需要了解的資訊。檢視可以簡化對資料的操作。
2.增加資料的安全性：通過檢視，使用者只能查詢和修改指定的資料，指定資料以外的資訊，使用者根本接觸不到。
資料庫授權命令可以限制使用者的操作許可權，但不能先知道特定行和列上。使用檢視後，可以簡單方便的將使用者的許可權先知道特定的行和列上。
保證敏感資訊不會被沒有許可權的人看到，保證一些機密資訊的安全。
3.提高表的邏輯獨立性：檢視可以遮蔽原有表結構變化帶來的影響。原有增加列、刪除列和未被引用的列，對檢視不會造成影響。
同樣，如果修改了表中的某些列，可以使用修改檢視來解決這系列帶來的影響。
8.2建立檢視
8.2.1建立檢視的語法形式
CREATE [ALGORITHM={UNDEFINED|MERGE|TEMPTABLE}] VIEW 檢視名 [(屬性清單)] AS SELECT 語句 [WITH [CASCADED|LOCAL] CHECK OPTION];
ALGORITHM 表示檢視選擇的演算法;UNDEFINED 是MySQL自動選擇所要使用的演算法， MERGE 表示將使用檢視的語句與檢視定義合併起來，使得檢視定義的某一部分取代語句對應的部分;TEMPTABLE 將檢視的結果存入臨時表，然後使用臨時表執行語句。
CASCADED 表示更新檢視時要滿足所有相關檢視和表的條件，該引數為預設值;LOCAL 表示更新檢視時，要滿足該檢視本身定義的條件即可。
技巧：使用 CREATE VIEW 語句建立檢視時，最好加上 WITH CHECK OPTION 引數，而且最好加上 CASCADED 引數。這樣，從檢視上派生出來的新檢視後，更新新檢視需要考慮其父檢視的約束條件。這種方式比較嚴格，可以保證資料的安全性。
建立檢視，需要有 CREATE VIEW 的許可權。
SELECT SELECT_priv,CREATE_view_priv FROM mysql.user WHERE user='root';
8.2.2 在單表上建立檢視
CREATE VIEW department_view1 AS SELECT * FROM department;
DESC department_view1;
建立帶屬性清單的檢視
CREATE VIEW department_view2(name,function,location)
AS SELECT d_name,function,address FROM department;
DESC department_view2;
8.2.3在多表上建立檢視
use test;
use job;
DESC department;
DESC department;
CREATE TABLE department(
d_id INT(4) NOT NULL PRIMARY KEY,
d_name VARCHAR(20) NOT NULL UNIQUE,
function VARCHAR(50),
address VARCHAR(50)
);
DESC worker;
CREATE ALGORITHM=MERGE VIEW worker_view1(name,department,sex,age,address)
AS SELECT name,department.d_name,sex,2009-birthday,worker.address FROM worker,department WHERE worker.d_id=department.d_id
WITH LOCAL CHECK OPTION;
2009-birthday 對應 age
DESC worker_view1;
8.3檢視檢視
DESCRIBE worker_view1;
DESC worker_view1;
8.3.2 SHOW TABLE STATUS LIKE '檢視名';檢視檢視基本資訊
SHOW TABLE STATUS LIKE 'worker_view1';
mysql> show table status like 'worker_view1';
+--------------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+-------------+-------------+------------+-----------+----------+----------------+---------+
| Name | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time | Update_time | Check_time | Collation | Checksum | Create_options | Comment |
+--------------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+-------------+-------------+------------+-----------+----------+----------------+---------+
| worker_view1 | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | VIEW |
+--------------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+-------------+-------------+------------+-----------+----------+----------------+---------+
表的說明(Comment)項的值為WIEW，說明該表為檢視。儲存引擎、資料長度等資訊顯示為 NULL ，說明該表是虛擬表，與普通表有差異。同樣使用 SHOW TABLE STATUS LIKE 'department';
mysql> show table status like 'department';
+------------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+-------------+------------+-----------------+----------+----------------+---------+
| Name | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time | Update_time | Check_time | Collation | Checksum | Create_options | Comment |
+------------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+-------------+------------+-----------------+----------+----------------+---------+
| department | InnoDB | 10 | Compact | 0 | 0 | 16384 | 0 | 16384 | 8388608 | NULL | 2015-05-07 03:30:39 | NULL | NULL | utf8_general_ci | NULL | | |
+------------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+-------------+------------+-----------------+----------+----------------+---------+
department表的基本資訊都顯示出來，包括儲存引擎、建立時間等。但是Comment項沒有資訊。這就是檢視和普通表最直接的區別。
使用 SHOW TABLE STATUS LIKE '表名/檢視名'; 檢視各個屬性顯示 NULL ，只有 Comment 顯示值為 VIEW。而普通表各個屬性顯示正常，只有 Comment 無任何顯示。
8.3.3 SHOW CREATE VIEW 檢視檢視詳細(其實是所有)資訊
語句 SHOW CREATE VIEW 檢視名;
SHOW CREATE VIEW worker_view1;
mysql> SHOW CREATE VIEW worker_view1;
+--------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+
| View | Create View | character_set_client | collation_connection |
+--------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+
| worker_view1 | CREATE ALGORITHM=MERGE DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `worker_view1` AS select `worker`.`name` AS `name`,`department`.`d_name` AS `department`,`worker`.`sex` AS `sex`,(2009 - `worker`.`birthday`) AS `age`,`worker`.`address` AS `address` from (`worker` join `department`) where (`worker`.`d_id` = `department`.`d_id`) WITH LOCAL CHECK OPTION | utf8 | utf8_general_ci |
+--------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+
8.3.4 在 VIEWS 表中查詢所有檢視詳細資訊，通常情況下使用 SHOW CREATE VIEW 檢視名; 進行查詢
SELECT * FROM information_schema.VIEWS;
8.4修改檢視
①. CREATE OR REPLACE VIEW
②. ALTER
8.4.1 CREATE OR REPLACE VIEW 語句修改檢視
語句： CREATE OR REPLACE VIEW [ALGORITHM={UNDEFINED|MERGE|TEMPTABLE}] VIEW 檢視名 [(屬性清單)] AS SELECT 語句 [WITH [CASCADED|LOCAL] CHECK OPTION];
eg: CREATE OR REPLACE ALGORITHM=TEMPTABLE VIEW department_view1(department,function,location) AS SELECT d_name,function,address FROM department;
DESC department_view1;
8.4.2 ALTER 語句修改檢視
語句： ALTER [ALGORITHM={UNDEFINED|MERGE|TEMPTABLE}] VIEW 檢視名 [(屬性清單)] AS SELECT 語句 [WITH [CASCADED|LOCAL] CHECK OPTION];
eg:
ALTER VIEW department_view2(department,name,sex,location)
AS SELECT d_name,worker.name,worker.sex,worker.address
FROM department,worker
WHERE department.d_id=worker.d_id
WITH CHECK OPTION;
8.5 更新檢視
包括插入（INSERT）、更新（UPDATA）、刪除(DELETE)表中的資料。
SELECT * from department;
INSERT INTO department VALUES
(1001,'人事部','管理公司人事變動','2號樓3層'),
(1002,'生產部','主管生產','5號樓1層');
CREATE VIEW department_view3(name,function,address)
AS SELECT d_name,function,address
FROM department
WHERE d_id=1001;
SELECT * FROM department_view3;
等價於
UPDATE department SET d_name='科研部',function='新產品研發',address='3號樓5層' WHERE d_id=1001;
不可更新的檢視：
①檢視中含有 SUM()、COUNT()、MAX()、MIN()等函式
eg: CREATE VIEW worker_view4(name,sex,total)
AS SELECT name,sex,COUNT(name) FROM worker;
②檢視中包含 UNION/UNION ALL/DISTINCT/GROUP BY/HAVING 等關鍵字。
eg: CREATE VIEW worker_view5(name,sex,address) AS SELECT name,sex,homeaddress FROM worker GROUP BY d_id;
③常量檢視
eg: CREATE VIEW worker_view6 AS SELECT 'Aric' as name;
mysql > UPDATE worker_view6 SET name='aaa';
ERROR 1228(HY000):The target table worker_view6 of the UPDATE is not updatable
④檢視中包含子查詢
eg: CREATE VIEW worker_view7(name) AS SELECT (SELECT name FROM worker);
⑤由不可更新的檢視匯出的檢視
eg: CREATE VIEW worker_view8 AS SELECT * FROM worker_view7;
mysql > UPDATE worker_view8 SET name='Aric';
ERROR 1288(HY00):The target table worker_view8 of the UPDATE is not updatable
⑥建立檢視時， ALGORITHM 為 TEMPTABLE 型別。
eg: CREATE ALGORITHM=TEMPTABLE VIEW worker_view9 AS SELECT * FROM worker;
⑦試圖對應的表上存在沒有預設值的列，而且該列沒有包含在視圖裡。
⑧ WITH [CASCADED|LOCAL] CHECK OPTION也將決定檢視是否更新。沒有指明時，預設為 CASCADED
eg:
mysql > CREATE VIEW view_test AS SELECT * FROM worker WHERE age<25 WITH LOCAL CHECK OPTION;
mysql > CREATE VIEW view_test1 AS SELECT * FROM view_test WHERE age>15 WITH LOCAL CHECK OPTION;
mysql > CREATE VIEW view_test2 AS SELECT * FROM worker WHERE sex='F' WITH CASCADED CHECK OPTION;
view_test1 和 view_test2 這兩個檢視是在 view_test 的基礎上建立而成的。
更新 view_test1
mysql > UPDATE view_test1 SET age=26 WHERE num=1; 試圖更新成功，因為條件 age=26 滿足 view_test1 中 age>15 的條件。
更新 view_test2
mysql > UPDATE view_test2 SET age=26 WHERE num=2; ERROR : CHECK OPTION failed.... 檢視二更新失敗是因為不滿足檢視 view_test 中 age<25 的條件，所以更新失敗。
8.6 刪除檢視
刪除檢視是指刪除資料庫中已存在的檢視。刪除檢視時，只能刪除檢視的定義，不會刪除檢視的資料。
語句 ： DROP VIEW [IF EXISTS] 檢視名列表 [RESTRICT|CASCADE]
eg: DROP VIEW IF EXISTS worker_view1;
mysql > SHOW CREATE VIEW worker_view1; ERROR :TABLE doesnot EXIST.
同時刪除兩個檢視
eg: DROP VIEW IF EXISTS department_view1,department_view2;
mysql > SHOW CREATE VIEW department_view1; ERROR : TABLE doesnot EXIST
mysql > SHOW CREATE VIEW department_view2; ERROR : TABLE doesnot EXIST
檢視使用者的 DROP 許可權
mysql > SELECT DROP_priv FROM mysql.user WHERE user='root';
+-----------+
| drop_priv |
+-----------+
| Y |
+-----------+
CREATE TABLE work_info(
id INT(10) PRIMARY KEY NOT NULL UNIQUE,#編號
name VARCHAR(20) NOT NULL,#姓名
sex VARCHAR(4) NOT NULL,#性別
age INT(5),#年齡
address VARCHAR(50),#家庭住址
tel VARCHAR(20)#電話號碼
);
CREATE TABLE college(
number INT(10) PRIMARY KEY NOT NULL UNIQUE,#學號
name VARCHAR(20) NOT NULL,#姓名
major VARCHAR(20) NOT NULL,#專業
age INT(5)#年齡
);
CREATE TABLE mytable(
id INT(10) PRIMARY KEY NOT NULL UNIQUE,#編號
name VARCHAR(20) NOT NULL,#姓名
sex VARCHAR(4),#性別
info text#備註
);
第九章 觸發器
觸發器(TRIGGER)是由事件來觸發某個操作。這些事件包括 INSERT 語句, UPDATE , DELETE 語句。eg:當學生表中增加了一個學生的資訊時，學生的總數就必須同時改變。可以在這裡建立一個觸發器，每次增加一個學生的記錄，就執行一次計算學生總數的操作。這樣就可以保證，每次增加學生的紀錄後，學生總數與記錄數是一致的。觸發器觸發的執行語句只有一個，也可能有多個。
語句: CREATE TRIGGER 觸發器名 BEFORE|AFTER 觸發事件 ON 表名 FOR EACH ROW 執行語句;
BEFORE|AFTER 引數指定了觸發器執行的時間,BEFORE 指出發時間之前執行處罰語句,AFTER 表示在觸發事件之後執行觸發語句;"觸發事件"引數是指觸發的條件，其中包括 INSERT 、 UPDATE 、 DELETE 。"表名" 引數觸發事件操作的標的名稱; FOR EACH ROW 表示任何一條記錄上的操作滿足觸發事件都會觸發該觸發器;"執行語句" 引數指觸發器被觸發後執行的程式。
eg:
①建立表
CREATE TABLE trigger_time(
exec_time time
);
②建立觸發器
CREATE TRIGGER dept_trig1 BEFORE INSERT ON department FOR EACH ROW INSERT INTO trigger_time VALUES(NOW());
③向 department 表插入資料
SELECT * FROM department;
INSERT INTO department VALUES(1003,'銷售部','負責產品生產','1號樓銷售大廳');
④檢視是否引發觸發器
SELECT * FROM trigger_time;
9.1.2 建立有多個執行語句的觸發器
語句:
delimiter &&
CREATE TRIGGER 觸發器名 BEFORE|AFTER 觸發事件
ON 表名 FOR EACH ROW
BEGIN
執行語句1;
執行語句2;
END &&
delimiter;
eg:
①建立觸發器
delimiter &&
CREATE TRIGGER dept_trig2 AFTER DELETE
ON department FOR EACH ROW
BEGIN
INSERT INTO trigger_time VALUES('21:01:01');
INSERT INTO trigger_time VALUES('22:01:01');
END &&
delimiter;
②刪除資料語句
DELETE FROM department WHERE d_id=1003;
SELECT * FROM trigger_time;
注意：MySQL中，一個表在相同觸發時間的相同觸發事件，只能建立一個觸發器。
9.2檢視觸發器
9.2.1 SHOW TRIGGERS 語句檢視觸發器資訊
語句:
SHOW TRIGGERS;檢視所有觸發器的詳細資訊
mysql> show triggers;
+------------+--------+------------+---------------------------------------------------------------------------------------------------+--------+---------+----------------------------------------------------------------+----------------+----------------------+----------------------+--------------------+
| Trigger | Event | Table | Statement | Timing | Created | sql_mode | Definer | character_set_client | collation_connection | Database Collation |
+------------+--------+------------+---------------------------------------------------------------------------------------------------+--------+---------+----------------------------------------------------------------+----------------+----------------------+----------------------+--------------------+
| dept_trig1 | INSERT | department | INSERT INTO trigger_time VALUES(NOW()) | BEFORE | NULL | STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
| dept_trig2 | DELETE | department | BEGIN
INSERT INTO trigger_time VALUES('21:01:01');
INSERT INTO trigger_time VALUES('22:01:01');
END | AFTER | NULL | STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
+------------+--------+------------+---------------------------------------------------------------------------------------------------+--------+---------+----------------------------------------------------------------+----------------+----------------------+----------------------+--------------------+
查詢指定觸發器的詳細資訊
語句: SELECT * FROM information_schema.triggers WHERE trigger_name='觸發器名';
eg: SELECT * FROM information_schema.triggers WHERE trigger_name='dept_trig1';
mysql> select * from information_schema.triggers where trigger_name='dept_trig1';
+-----------------+----------------+--------------+--------------------+----------------------+---------------------+--------------------+--------------+------------------+----------------------------------------+--------------------+---------------+----------------------------+----------------------------+--------------------------+--------------------------+---------+----------------------------------------------------------------+----------------+----------------------+----------------------+--------------------+
| TRIGGER_CATALOG | TRIGGER_SCHEMA | TRIGGER_NAME | EVENT_MANIPULATION | EVENT_OBJECT_CATALOG | EVENT_OBJECT_SCHEMA | EVENT_OBJECT_TABLE | ACTION_ORDER | ACTION_CONDITION | ACTION_STATEMENT | ACTION_ORIENTATION | ACTION_TIMING | ACTION_REFERENCE_OLD_TABLE | ACTION_REFERENCE_NEW_TABLE | ACTION_REFERENCE_OLD_ROW | ACTION_REFERENCE_NEW_ROW | CREATED | SQL_MODE | DEFINER | CHARACTER_SET_CLIENT | COLLATION_CONNECTION | DATABASE_COLLATION |
+-----------------+----------------+--------------+--------------------+----------------------+---------------------+--------------------+--------------+------------------+----------------------------------------+--------------------+---------------+----------------------------+----------------------------+--------------------------+--------------------------+---------+----------------------------------------------------------------+----------------+----------------------+----------------------+--------------------+
| def | test | dept_trig1 | INSERT | def | test | department | 0 | NULL | INSERT INTO trigger_time VALUES(NOW()) | ROW | BEFORE | NULL | NULL | OLD | NEW | NULL | STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
+-----------------+----------------+--------------+--------------------+----------------------+---------------------+--------------------+--------------+------------------+----------------------------------------+--------------------+---------------+----------------------------+----------------------------+--------------------------+--------------------------+---------+----------------------------------------------------------------+----------------+----------------------+----------------------+--------------------+
9.3 觸發器的使用
DROP TABLE trigger_test;
CREATE TABLE trigger_test(
id INT(4) PRIMARY KEY UNIQUE NOT NULL auto_increment,
info VARCHAR(30)
);
DROP TRIGGER dept_trig1;
DROP TRIGGER before_insert;
delimiter &&
CREATE TRIGGER before_insert BEFORE INSERT
ON department FOR EACH ROW
BEGIN
INSERT INTO trigger_test VALUES(NULL,"before_insert");
END &&
delimiter;
DROP TRIGGER dept_trig2;
DROP TRIGGER after_insert;
delimiter &&
CREATE TRIGGER after_insert AFTER INSERT
ON department FOR EACH ROW
BEGIN
INSERT INTO trigger_test VALUES(NULL,"after_insert");
END &&
delimiter;
DELETE FROM department WHERE d_id=1003;
INSERT INTO department VALUES(1003,'銷售部','負責產品生產','1號銷售大廳');
SELECT * FROM trigger_test;
在啟用觸發器時，對觸發器中的執行語句存在一些限制。例如，觸發器不能包含 START TRANSACTION/COMMIT/ROLLBACK 等關鍵詞，也不能包含 CALL 語句。
在觸發器執行過程中，任何步驟出錯都會阻止程式向下執行。
9.4刪除觸發器
語句: DROP TRIGGER 觸發器名;
eg: DROP TRIGGER dept_trig1;
mysql> select * from information_schema.triggers where trigger_name='dept_trig1';
Empty set
CREATE TABLE product(
id INT(10) PRIMARY KEY NOT NULL UNIQUE,#編號
name VARCHAR(20) NOT NULL,#產品功能
function VARCHAR(50),#主要功能
company VARCHAR(20),#生產廠商
address VARCHAR(50)#家庭住址
);
CREATE TABLE operate(
op_id INT(10) PRIMARY KEY NOT NULL UNIQUE auto_increment,#編號
op_type VARCHAR(20) NOT NULL,#操作方式
op_time time NOT NULL#操作時間
);
CREATE TRIGGER product_af_del AFTER DELETE
ON product FOR EACH ROW
INSERT INTO operate VALUES(NULL,'Delete product',NOW());
第十章 查詢資料
10.1基本查詢語句
語句:
SELECT 屬性列表 FROM 表名和檢視列表
[WHERE 條件表示式1]
[GROUP BY 屬性名1 [HAVING 條件表示式2]]
[ORDER BY 屬性名2 [ASC|DESC]]
CREATE TABLE employee(
num INT(4) PRIMARY KEY UNIQUE NOT NULL,
d_id INT(4) NOT NULL,
name VARCHAR(20) NOT NULL,
age INT(4) NOT NULL,
sex VARCHAR(10),
homeaddr VARCHAR(30)
);
INSERT INTO employee VALUES
(1,1001,'張三',26,'男','北京市海淀區'),
(2,1001,'李四',24,'女','北京市昌平區'),
(3,1002,'王五',25,'男','湖南長沙市'),
(4,1004,'Aric',15,'男','England');
SELECT num,name,age,sex,homeaddr FROM employee;
SELECT * FROM employee;
SELECT * FROM employee WHERE d_id IN(1001,1004);
SELECT * FROM employee WHERE name NOT IN('張三','李四');
SELECT * FROM employee WHERE age BETWEEN 15 AND 25;
SELECT * FROM employee WHERE age NOT BETWEEN 15 AND 25;
SELECT * FROM employee WHERE name LIKE 'Aric';
SELECT * FROM employee WHERE name='Aric';
SELECT * FROM employee WHERE homeaddr LIKE '北京%'; %任意字元(萬用字元)
SELECT * FROM employee WHERE name like 'Ar_c'; _代表一個字元
SELECT * FROM employee WHERE name NOT LIKE '張%';
SELECT * FROM work WHERE info is NULL;
SELECT * FROM work WHERE info is NOT NULL;
SELECT * FROM employee WHERE d_id=1001 AND sex LIKE '男';
SELECT * FROM employee WHERE d_id<1004 AND age<26 AND sex='男';
SELECT * employee WHERE num IN(1,2,3) AND age BETWEEN 15 AND 25 AND homeaddr LIKE '%北京市%';
SELECT * FROM employee WHERE d_id=1001 OR sex LIKE '男';
SELECT * FROM employee WHERE num IN(1,2,3) OR age BETWEEN 24 AND 25 OR homeaddr like '%北京市%';
SELECT * FROM employee WHERE num IN(1,3,4) AND age=25 OR sex='女';
SELECT * FROM employee WHERE sex='女' OR num IN(1,3,4) AND age=25;
SELECT DISTINCT d_id FROM employee;
SELECT * FROM employee ORDER BY age;
SELECT * FROM employee ORDER BY age DESC;
SELECT * FROM employee ORDER BY d_id ASC,age DESC;
10.2.12 分組查詢
語句: GROUP BY [HAVING 條件表示式][WITH ROLLUP];
GROUP BY 關鍵字可以和 GROUP_CONCAT() 函式一起使用。 GROUP_CONCAT() 函式會把每個分組中指定欄位值都顯示出來。同時， GROUP BY 關鍵字通常與集合函式一起使用。集合函式包括 COUNT()/SUM()/AVG()/MAX()/MIN()
SELECT * FROM employee GROUP BY sex;
SELECT sex,GROUP_CONCAT(name) FROM employee GROUP BY sex;
+-----+--------------------+
| sex | GROUP_CONCAT(name) |
+-----+--------------------+
| 女 | 李四 |
| 男 | 張三,王五,Aric |
+-----+--------------------+
SELECT sex,COUNT(sex) FROM employee GROUP BY sex;
SELECT sex,COUNT(sex) FROM employee GROUP BY sex HAVING COUNT(sex)>=3;
SELECT * FROM employee FROM GROUP BY d_id,sex; 先按d_id分組， 再按sex分組
SELECT sex,COUNT(sex) FROM employee GROUP BY sex WITH ROLLUP; WITH ROLLUP 在資料記錄的最後統計一個記錄數總和，跟 COUNT() 連用。
SELECT sex,COUNT(sex) FROM employee GROUP BY sex WITH ROLLUP;
10.2.12 用 LIMIT 限制查詢結果的數量
1.不指定初始位置
eg:
SELECT * FROM employee LIMIT 2; 從初始位置開始，顯示前兩條記錄
SELECT * FROM employee LIMIT 6; 從初始位置開始，顯示前6條記錄，如果不足6條，則顯示有的全部記錄。
2.指定初始位置
SELECT * FROM employee LIMIT 0,2;從初始位置開始，顯示前兩條記錄，"0"代表初始位置
SELECT * FROM employee LIMIT 1,2;從第2條記錄開始，顯示兩條記錄
10.3集合函式查詢
10.3.1 COUNT()
SELECT COUNT(*) FROM employee;
SELECT d_id,COUNT(*) FROM employee GROUP BY d_id;
10.3.2 SUM()函式
SELECT * FROM grade;
SELECT num,SUM(score) FROM grade WHERE num=1001;
10.3.3 AVG()函式
SELECT AVG(age) FROM employee;
SELECT course,AVG(score) FROM grade GROUP BY course;
10.3.4 MAX()函式
SELECT MAX(age) FROM employee;
SELECT course,MAX(score) FROM grade GROUP BY course;
SELECT MAX(name) FROM work;
SELECT MIN(age) FROM age;
SELECT course,MIN(score) FROM grade GROUP BY course;
內連線
SELECT num,name,employee.d_id,age,sex,d_name,function FROM employee,department WHERE employee.d_id=department.d_id;
外連線
①左連線 eg:
SELECT num,name,employee.d_id,age,sex,d_name,function FROM employee LEFT JOIN department ON employee.d_id=department.d_id;
②右連線 eg:
SELECT num,name,employee.d_id,age,sex,d_name,function FROM employee RIGHT JOIN department ON employee.d_id=department.d_id;
10.4.3 複合條件連線查詢
SELECT num,name,employee,d_id,age,sex,d_name,function FROM employee,department WHERE employee.d_id=department.d_id AND age>24;
SELECT num,name,employee,d_id,age,sex,d_name,function FROM employee,department WHERE employee.d_id=department.d_id ORDER BY age ASC;
10.5 子查詢
IN eg:
SELECT * FROM employee WHERE d_id IN(SELECT d_id FROM department);
SELECT * FROM employee WHERE d_id NOT IN(SELECT d_id FROM department);
10.5.2 帶比較運算子的子查詢
CREATE TABLE scholarship(
level INT(4),
score INT(4)
);
INSERT INTO scholarship VALUES
(1,90),
(2,80),
(3,70);
CREATE TABLE computer_stu(
id INT(4)PRIMARY KEY NOT NULL,
name VARCHAR(30) NOT NULL,
score INT(4) NOT NULL
);
INSERT INTO computer_stu VALUES
(1001,'Lily',85),
(1002,'Tom',91),
(1003,'Jim',87),
(1004,'Aric',77),
(1005,'Lucy',65),
(1006,'Andy',99),
(1007,'Ada',85),
(1008,'Jeck',70);
SELECT id,name,score FROM computer_stu WHERE score>=
(SELECT score FROM scholarship WHERE LEVEL=1);
SELECT * FROM employee;
SELECT * FROM department;
SELECT d_id,d_name FROM department WHERE d_id!=
(SELECT d_id FROM employee WHERE age=24);
SELECT d_id,d_name FROM department WHERE d_id<>
(SELECT d_id FROM employee WHERE age=24);
10.5.3 帶 EXISTS 關鍵字的子查詢 內層語句不返回記錄，只返回真假值;當內層語句返回值為真，則進行外層查詢
SELECT * FROM employee;
SELECT * FROM department;
SELECT * FROM employee WHERE EXISTS
(SELECT d_name FROM department WHERE d_id=1003);
SELECT * FROM employee WHERE EXISTS
(SELECT d_name FROM department WHERE d_id=1004);
SELECT * FROM employee WHERE age>24 AND EXISTS
(SELECT d_name FROM department WHERE d_id=1003);
SELECT * FROM employee WHERE NOT EXISTS
(SELECT d_name FROM department WHERE d_id=1003); 因為內層語句返回記錄，故 NOT EXISTS 為假
10.5.4 帶 ANY 關鍵字的子查詢
SELECT * FROM computer_stu;
SELECT * FROM scholarship;
SELECT * FROM computer_stu
WHERE score>=ANY
(SELECT score FROM scholarship);
10.5.5 帶 ALL 關鍵字的子查詢
SELECT * FROM computer_stu WHERE score>=ALL
(SELECT score FROM scholarship);
10.6 合併查詢結果 UNION/ UNION ALL
UNION 將所有查詢結果合併到一起，去除掉相同的
UNION ALL 關鍵字則只是簡單的合併到一起
語句: SELECT 語句1 UNION|UNION ALL SELECT語句2 UNION|UNION ALL SELECT語句n;
SELECT d_id FROM department UNION SELECT d_id FROM employee;
SELECT d_id FROM department UNION ALL SELECT d_id FROM employee;
10.7 位表和欄位取別名
10.7.1 為表取名
SELECT * FROM department d WHERE d.d_id=1001;
10.7.2 為欄位取別名
語句: 屬性名 [AS] 別名
SELECT d_id AS department_id, d_name AS department_name FROM department;
SELECT d.d_id AS department_id,d.d_name AS department_name,d.function,d.address FROM department d WHERE d.d_id=1001;
10.8 使用正則表示式查詢
試圖是從一個或多個表中匯出來的表，是一種虛擬存在的表。檢視就像一個視窗，通過這個視窗，可以看到系統專門提供的資料。這樣，使用者可以只看到對自己有用的資料，而不用看到整個資料表中的其他資料。
8.1檢視簡介
8.1.1 檢視是一種虛擬的表，是從資料庫中一個或多個表中匯出來的表。檢視還可以從已經存在的檢視的基礎上定義。
資料庫中只存在了檢視的定義，而並沒有存放檢視中的資料。使用檢視進行查詢時，資料庫系統會從原來的表中取出對應的資料。
檢視是在原有的表或者檢視的基礎上重新定義的虛擬表，這可以從原有的表上選取對使用者有用的資訊。那些對使用者沒用，或者使用者沒有許可權去了解的資訊，都可以直接遮蔽掉。
這樣既使應用簡單化，也保證了系統的安全。
檢視的作用：
1.使操作簡單化：檢視需要達到的目的是所見即所需。從試圖看到的資訊就是所需要了解的資訊。檢視可以簡化對資料的操作。
2.增加資料的安全性：通過檢視，使用者只能查詢和修改指定的資料，指定資料以外的資訊，使用者根本接觸不到。
資料庫授權命令可以限制使用者的操作許可權，但不能先知道特定行和列上。使用檢視後，可以簡單方便的將使用者的許可權先知道特定的行和列上。
保證敏感資訊不會被沒有許可權的人看到，保證一些機密資訊的安全。
3.提高表的邏輯獨立性：檢視可以遮蔽原有表結構變化帶來的影響。原有增加列、刪除列和未被引用的列，對檢視不會造成影響。
同樣，如果修改了表中的某些列，可以使用修改檢視來解決這系列帶來的影響。
8.2建立檢視
8.2.1建立檢視的語法形式
CREATE [ALGORITHM={UNDEFINED|MERGE|TEMPTABLE}] VIEW 檢視名 [(屬性清單)] AS SELECT 語句 [WITH [CASCADED|LOCAL] CHECK OPTION];
ALGORITHM 表示檢視選擇的演算法;UNDEFINED 是MySQL自動選擇所要使用的演算法， MERGE 表示將使用檢視的語句與檢視定義合併起來，使得檢視定義的某一部分取代語句對應的部分;TEMPTABLE 將檢視的結果存入臨時表，然後使用臨時表執行語句。
CASCADED 表示更新檢視時要滿足所有相關檢視和表的條件，該引數為預設值;LOCAL 表示更新檢視時，要滿足該檢視本身定義的條件即可。
技巧：使用 CREATE VIEW 語句建立檢視時，最好加上 WITH CHECK OPTION 引數，而且最好加上 CASCADED 引數。這樣，從檢視上派生出來的新檢視後，更新新檢視需要考慮其父檢視的約束條件。這種方式比較嚴格，可以保證資料的安全性。
建立檢視，需要有 CREATE VIEW 的許可權。
SELECT SELECT_priv,CREATE_view_priv FROM mysql.user WHERE user='root';
8.2.2 在單表上建立檢視
CREATE VIEW department_view1 AS SELECT * FROM department;
DESC department_view1;
建立帶屬性清單的檢視
CREATE VIEW department_view2(name,function,location)
AS SELECT d_name,function,address FROM department;
DESC department_view2;
8.2.3在多表上建立檢視
use test;
use job;
DESC department;
DESC department;
CREATE TABLE department(
d_id INT(4) NOT NULL PRIMARY KEY,
d_name VARCHAR(20) NOT NULL UNIQUE,
function VARCHAR(50),
address VARCHAR(50)
);
DESC worker;
CREATE ALGORITHM=MERGE VIEW worker_view1(name,department,sex,age,address)
AS SELECT name,department.d_name,sex,2009-birthday,worker.address FROM worker,department WHERE worker.d_id=department.d_id
WITH LOCAL CHECK OPTION;
2009-birthday 對應 age
DESC worker_view1;
8.3檢視檢視
DESCRIBE worker_view1;
DESC worker_view1;
8.3.2 SHOW TABLE STATUS LIKE '檢視名';檢視檢視基本資訊
SHOW TABLE STATUS LIKE 'worker_view1';
mysql> show table status like 'worker_view1';
+--------------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+-------------+-------------+------------+-----------+----------+----------------+---------+
| Name | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time | Update_time | Check_time | Collation | Checksum | Create_options | Comment |
+--------------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+-------------+-------------+------------+-----------+----------+----------------+---------+
| worker_view1 | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | VIEW |
+--------------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+-------------+-------------+------------+-----------+----------+----------------+---------+
表的說明(Comment)項的值為WIEW，說明該表為檢視。儲存引擎、資料長度等資訊顯示為 NULL ，說明該表是虛擬表，與普通表有差異。同樣使用 SHOW TABLE STATUS LIKE 'department';
mysql> show table status like 'department';
+------------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+-------------+------------+-----------------+----------+----------------+---------+
| Name | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time | Update_time | Check_time | Collation | Checksum | Create_options | Comment |
+------------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+-------------+------------+-----------------+----------+----------------+---------+
| department | InnoDB | 10 | Compact | 0 | 0 | 16384 | 0 | 16384 | 8388608 | NULL | 2015-05-07 03:30:39 | NULL | NULL | utf8_general_ci | NULL | | |
+------------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+-------------+------------+-----------------+----------+----------------+---------+
department表的基本資訊都顯示出來，包括儲存引擎、建立時間等。但是Comment項沒有資訊。這就是檢視和普通表最直接的區別。
使用 SHOW TABLE STATUS LIKE '表名/檢視名'; 檢視各個屬性顯示 NULL ，只有 Comment 顯示值為 VIEW。而普通表各個屬性顯示正常，只有 Comment 無任何顯示。
8.3.3 SHOW CREATE VIEW 檢視檢視詳細(其實是所有)資訊
語句 SHOW CREATE VIEW 檢視名;
SHOW CREATE VIEW worker_view1;
mysql> SHOW CREATE VIEW worker_view1;
+--------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+
| View | Create View | character_set_client | collation_connection |
+--------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+
| worker_view1 | CREATE ALGORITHM=MERGE DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `worker_view1` AS select `worker`.`name` AS `name`,`department`.`d_name` AS `department`,`worker`.`sex` AS `sex`,(2009 - `worker`.`birthday`) AS `age`,`worker`.`address` AS `address` from (`worker` join `department`) where (`worker`.`d_id` = `department`.`d_id`) WITH LOCAL CHECK OPTION | utf8 | utf8_general_ci |
+--------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+
8.3.4 在 VIEWS 表中查詢所有檢視詳細資訊，通常情況下使用 SHOW CREATE VIEW 檢視名; 進行查詢
SELECT * FROM information_schema.VIEWS;
8.4修改檢視
①. CREATE OR REPLACE VIEW
②. ALTER
8.4.1 CREATE OR REPLACE VIEW 語句修改檢視
語句： CREATE OR REPLACE VIEW [ALGORITHM={UNDEFINED|MERGE|TEMPTABLE}] VIEW 檢視名 [(屬性清單)] AS SELECT 語句 [WITH [CASCADED|LOCAL] CHECK OPTION];
eg: CREATE OR REPLACE ALGORITHM=TEMPTABLE VIEW department_view1(department,function,location) AS SELECT d_name,function,address FROM department;
DESC department_view1;
8.4.2 ALTER 語句修改檢視
語句： ALTER [ALGORITHM={UNDEFINED|MERGE|TEMPTABLE}] VIEW 檢視名 [(屬性清單)] AS SELECT 語句 [WITH [CASCADED|LOCAL] CHECK OPTION];
eg:
ALTER VIEW department_view2(department,name,sex,location)
AS SELECT d_name,worker.name,worker.sex,worker.address
FROM department,worker
WHERE department.d_id=worker.d_id
WITH CHECK OPTION;
8.5 更新檢視
包括插入（INSERT）、更新（UPDATA）、刪除(DELETE)表中的資料。
SELECT * from department;
INSERT INTO department VALUES
(1001,'人事部','管理公司人事變動','2號樓3層'),
(1002,'生產部','主管生產','5號樓1層');
CREATE VIEW department_view3(name,function,address)
AS SELECT d_name,function,address
FROM department
WHERE d_id=1001;
SELECT * FROM department_view3;
等價於
UPDATE department SET d_name='科研部',function='新產品研發',address='3號樓5層' WHERE d_id=1001;
不可更新的檢視：
①檢視中含有 SUM()、COUNT()、MAX()、MIN()等函式
eg: CREATE VIEW worker_view4(name,sex,total)
AS SELECT name,sex,COUNT(name) FROM worker;
②檢視中包含 UNION/UNION ALL/DISTINCT/GROUP BY/HAVING 等關鍵字。
eg: CREATE VIEW worker_view5(name,sex,address) AS SELECT name,sex,homeaddress FROM worker GROUP BY d_id;
③常量檢視
eg: CREATE VIEW worker_view6 AS SELECT 'Aric' as name;
mysql > UPDATE worker_view6 SET name='aaa';
ERROR 1228(HY000):The target table worker_view6 of the UPDATE is not updatable
④檢視中包含子查詢
eg: CREATE VIEW worker_view7(name) AS SELECT (SELECT name FROM worker);
⑤由不可更新的檢視匯出的檢視
eg: CREATE VIEW worker_view8 AS SELECT * FROM worker_view7;
mysql > UPDATE worker_view8 SET name='Aric';
ERROR 1288(HY00):The target table worker_view8 of the UPDATE is not updatable
⑥建立檢視時， ALGORITHM 為 TEMPTABLE 型別。
eg: CREATE ALGORITHM=TEMPTABLE VIEW worker_view9 AS SELECT * FROM worker;
⑦試圖對應的表上存在沒有預設值的列，而且該列沒有包含在視圖裡。
⑧ WITH [CASCADED|LOCAL] CHECK OPTION也將決定檢視是否更新。沒有指明時，預設為 CASCADED
eg:
mysql > CREATE VIEW view_test AS SELECT * FROM worker WHERE age<25 WITH LOCAL CHECK OPTION;
mysql > CREATE VIEW view_test1 AS SELECT * FROM view_test WHERE age>15 WITH LOCAL CHECK OPTION;
mysql > CREATE VIEW view_test2 AS SELECT * FROM worker WHERE sex='F' WITH CASCADED CHECK OPTION;
view_test1 和 view_test2 這兩個檢視是在 view_test 的基礎上建立而成的。
更新 view_test1
mysql > UPDATE view_test1 SET age=26 WHERE num=1; 試圖更新成功，因為條件 age=26 滿足 view_test1 中 age>15 的條件。
更新 view_test2
mysql > UPDATE view_test2 SET age=26 WHERE num=2; ERROR : CHECK OPTION failed.... 檢視二更新失敗是因為不滿足檢視 view_test 中 age<25 的條件，所以更新失敗。
8.6 刪除檢視
刪除檢視是指刪除資料庫中已存在的檢視。刪除檢視時，只能刪除檢視的定義，不會刪除檢視的資料。
語句 ： DROP VIEW [IF EXISTS] 檢視名列表 [RESTRICT|CASCADE]
eg: DROP VIEW IF EXISTS worker_view1;
mysql > SHOW CREATE VIEW worker_view1; ERROR :TABLE doesnot EXIST.
同時刪除兩個檢視
eg: DROP VIEW IF EXISTS department_view1,department_view2;
mysql > SHOW CREATE VIEW department_view1; ERROR : TABLE doesnot EXIST
mysql > SHOW CREATE VIEW department_view2; ERROR : TABLE doesnot EXIST
檢視使用者的 DROP 許可權
mysql > SELECT DROP_priv FROM mysql.user WHERE user='root';
+-----------+
| drop_priv |
+-----------+
| Y |
+-----------+
CREATE TABLE work_info(
id INT(10) PRIMARY KEY NOT NULL UNIQUE,#編號
name VARCHAR(20) NOT NULL,#姓名
sex VARCHAR(4) NOT NULL,#性別
age INT(5),#年齡
address VARCHAR(50),#家庭住址
tel VARCHAR(20)#電話號碼
);
CREATE TABLE college(
number INT(10) PRIMARY KEY NOT NULL UNIQUE,#學號
name VARCHAR(20) NOT NULL,#姓名
major VARCHAR(20) NOT NULL,#專業
age INT(5)#年齡
);
CREATE TABLE mytable(
id INT(10) PRIMARY KEY NOT NULL UNIQUE,#編號
name VARCHAR(20) NOT NULL,#姓名
sex VARCHAR(4),#性別
info text#備註
);
第九章 觸發器
觸發器(TRIGGER)是由事件來觸發某個操作。這些事件包括 INSERT 語句, UPDATE , DELETE 語句。eg:當學生表中增加了一個學生的資訊時，學生的總數就必須同時改變。可以在這裡建立一個觸發器，每次增加一個學生的記錄，就執行一次計算學生總數的操作。這樣就可以保證，每次增加學生的紀錄後，學生總數與記錄數是一致的。觸發器觸發的執行語句只有一個，也可能有多個。
語句: CREATE TRIGGER 觸發器名 BEFORE|AFTER 觸發事件 ON 表名 FOR EACH ROW 執行語句;
BEFORE|AFTER 引數指定了觸發器執行的時間,BEFORE 指出發時間之前執行處罰語句,AFTER 表示在觸發事件之後執行觸發語句;"觸發事件"引數是指觸發的條件，其中包括 INSERT 、 UPDATE 、 DELETE 。"表名" 引數觸發事件操作的標的名稱; FOR EACH ROW 表示任何一條記錄上的操作滿足觸發事件都會觸發該觸發器;"執行語句" 引數指觸發器被觸發後執行的程式。
eg:
①建立表
CREATE TABLE trigger_time(
exec_time time
);
②建立觸發器
CREATE TRIGGER dept_trig1 BEFORE INSERT ON department FOR EACH ROW INSERT INTO trigger_time VALUES(NOW());
③向 department 表插入資料
SELECT * FROM department;
INSERT INTO department VALUES(1003,'銷售部','負責產品生產','1號樓銷售大廳');
④檢視是否引發觸發器
SELECT * FROM trigger_time;
9.1.2 建立有多個執行語句的觸發器
語句:
delimiter &&
CREATE TRIGGER 觸發器名 BEFORE|AFTER 觸發事件
ON 表名 FOR EACH ROW
BEGIN
執行語句1;
執行語句2;
END &&
delimiter;
eg:
①建立觸發器
delimiter &&
CREATE TRIGGER dept_trig2 AFTER DELETE
ON department FOR EACH ROW
BEGIN
INSERT INTO trigger_time VALUES('21:01:01');
INSERT INTO trigger_time VALUES('22:01:01');
END &&
delimiter;
②刪除資料語句
DELETE FROM department WHERE d_id=1003;
SELECT * FROM trigger_time;
注意：MySQL中，一個表在相同觸發時間的相同觸發事件，只能建立一個觸發器。
9.2檢視觸發器
9.2.1 SHOW TRIGGERS 語句檢視觸發器資訊
語句:
SHOW TRIGGERS;檢視所有觸發器的詳細資訊
mysql> show triggers;
+------------+--------+------------+---------------------------------------------------------------------------------------------------+--------+---------+----------------------------------------------------------------+----------------+----------------------+----------------------+--------------------+
| Trigger | Event | Table | Statement | Timing | Created | sql_mode | Definer | character_set_client | collation_connection | Database Collation |
+------------+--------+------------+---------------------------------------------------------------------------------------------------+--------+---------+----------------------------------------------------------------+----------------+----------------------+----------------------+--------------------+
| dept_trig1 | INSERT | department | INSERT INTO trigger_time VALUES(NOW()) | BEFORE | NULL | STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
| dept_trig2 | DELETE | department | BEGIN
INSERT INTO trigger_time VALUES('21:01:01');
INSERT INTO trigger_time VALUES('22:01:01');
END | AFTER | NULL | STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
+------------+--------+------------+---------------------------------------------------------------------------------------------------+--------+---------+----------------------------------------------------------------+----------------+----------------------+----------------------+--------------------+
查詢指定觸發器的詳細資訊
語句: SELECT * FROM information_schema.triggers WHERE trigger_name='觸發器名';
eg: SELECT * FROM information_schema.triggers WHERE trigger_name='dept_trig1';
mysql> select * from information_schema.triggers where trigger_name='dept_trig1';
+-----------------+----------------+--------------+--------------------+----------------------+---------------------+--------------------+--------------+------------------+----------------------------------------+--------------------+---------------+----------------------------+----------------------------+--------------------------+--------------------------+---------+----------------------------------------------------------------+----------------+----------------------+----------------------+--------------------+
| TRIGGER_CATALOG | TRIGGER_SCHEMA | TRIGGER_NAME | EVENT_MANIPULATION | EVENT_OBJECT_CATALOG | EVENT_OBJECT_SCHEMA | EVENT_OBJECT_TABLE | ACTION_ORDER | ACTION_CONDITION | ACTION_STATEMENT | ACTION_ORIENTATION | ACTION_TIMING | ACTION_REFERENCE_OLD_TABLE | ACTION_REFERENCE_NEW_TABLE | ACTION_REFERENCE_OLD_ROW | ACTION_REFERENCE_NEW_ROW | CREATED | SQL_MODE | DEFINER | CHARACTER_SET_CLIENT | COLLATION_CONNECTION | DATABASE_COLLATION |
+-----------------+----------------+--------------+--------------------+----------------------+---------------------+--------------------+--------------+------------------+----------------------------------------+--------------------+---------------+----------------------------+----------------------------+--------------------------+--------------------------+---------+----------------------------------------------------------------+----------------+----------------------+----------------------+--------------------+
| def | test | dept_trig1 | INSERT | def | test | department | 0 | NULL | INSERT INTO trigger_time VALUES(NOW()) | ROW | BEFORE | NULL | NULL | OLD | NEW | NULL | STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
+-----------------+----------------+--------------+--------------------+----------------------+---------------------+--------------------+--------------+------------------+----------------------------------------+--------------------+---------------+----------------------------+----------------------------+--------------------------+--------------------------+---------+----------------------------------------------------------------+----------------+----------------------+----------------------+--------------------+
9.3 觸發器的使用
DROP TABLE trigger_test;
CREATE TABLE trigger_test(
id INT(4) PRIMARY KEY UNIQUE NOT NULL auto_increment,
info VARCHAR(30)
);
DROP TRIGGER dept_trig1;
DROP TRIGGER before_insert;
delimiter &&
CREATE TRIGGER before_insert BEFORE INSERT
ON department FOR EACH ROW
BEGIN
INSERT INTO trigger_test VALUES(NULL,"before_insert");
END &&
delimiter;
DROP TRIGGER dept_trig2;
DROP TRIGGER after_insert;
delimiter &&
CREATE TRIGGER after_insert AFTER INSERT
ON department FOR EACH ROW
BEGIN
INSERT INTO trigger_test VALUES(NULL,"after_insert");
END &&
delimiter;
DELETE FROM department WHERE d_id=1003;
INSERT INTO department VALUES(1003,'銷售部','負責產品生產','1號銷售大廳');
SELECT * FROM trigger_test;
在啟用觸發器時，對觸發器中的執行語句存在一些限制。例如，觸發器不能包含 START TRANSACTION/COMMIT/ROLLBACK 等關鍵詞，也不能包含 CALL 語句。
在觸發器執行過程中，任何步驟出錯都會阻止程式向下執行。
9.4刪除觸發器
語句: DROP TRIGGER 觸發器名;
eg: DROP TRIGGER dept_trig1;
mysql> select * from information_schema.triggers where trigger_name='dept_trig1';
Empty set
CREATE TABLE product(
id INT(10) PRIMARY KEY NOT NULL UNIQUE,#編號
name VARCHAR(20) NOT NULL,#產品功能
function VARCHAR(50),#主要功能
company VARCHAR(20),#生產廠商
address VARCHAR(50)#家庭住址
);
CREATE TABLE operate(
op_id INT(10) PRIMARY KEY NOT NULL UNIQUE auto_increment,#編號
op_type VARCHAR(20) NOT NULL,#操作方式
op_time time NOT NULL#操作時間
);
CREATE TRIGGER product_af_del AFTER DELETE
ON product FOR EACH ROW
INSERT INTO operate VALUES(NULL,'Delete product',NOW());
第十章 查詢資料
10.1基本查詢語句
語句:
SELECT 屬性列表 FROM 表名和檢視列表
[WHERE 條件表示式1]
[GROUP BY 屬性名1 [HAVING 條件表示式2]]
[ORDER BY 屬性名2 [ASC|DESC]]
CREATE TABLE employee(
num INT(4) PRIMARY KEY UNIQUE NOT NULL,
d_id INT(4) NOT NULL,
name VARCHAR(20) NOT NULL,
age INT(4) NOT NULL,
sex VARCHAR(10),
homeaddr VARCHAR(30)
);
INSERT INTO employee VALUES
(1,1001,'張三',26,'男','北京市海淀區'),
(2,1001,'李四',24,'女','北京市昌平區'),
(3,1002,'王五',25,'男','湖南長沙市'),
(4,1004,'Aric',15,'男','England');
SELECT num,name,age,sex,homeaddr FROM employee;
SELECT * FROM employee;
SELECT * FROM employee WHERE d_id IN(1001,1004);
SELECT * FROM employee WHERE name NOT IN('張三','李四');
SELECT * FROM employee WHERE age BETWEEN 15 AND 25;
SELECT * FROM employee WHERE age NOT BETWEEN 15 AND 25;
SELECT * FROM employee WHERE name LIKE 'Aric';
SELECT * FROM employee WHERE name='Aric';
SELECT * FROM employee WHERE homeaddr LIKE '北京%'; %任意字元(萬用字元)
SELECT * FROM employee WHERE name like 'Ar_c'; _代表一個字元
SELECT * FROM employee WHERE name NOT LIKE '張%';
SELECT * FROM work WHERE info is NULL;
SELECT * FROM work WHERE info is NOT NULL;
SELECT * FROM employee WHERE d_id=1001 AND sex LIKE '男';
SELECT * FROM employee WHERE d_id<1004 AND age<26 AND sex='男';
SELECT * employee WHERE num IN(1,2,3) AND age BETWEEN 15 AND 25 AND homeaddr LIKE '%北京市%';
SELECT * FROM employee WHERE d_id=1001 OR sex LIKE '男';
SELECT * FROM employee WHERE num IN(1,2,3) OR age BETWEEN 24 AND 25 OR homeaddr like '%北京市%';
SELECT * FROM employee WHERE num IN(1,3,4) AND age=25 OR sex='女';
SELECT * FROM employee WHERE sex='女' OR num IN(1,3,4) AND age=25;
SELECT DISTINCT d_id FROM employee;
SELECT * FROM employee ORDER BY age;
SELECT * FROM employee ORDER BY age DESC;
SELECT * FROM employee ORDER BY d_id ASC,age DESC;
10.2.12 分組查詢
語句: GROUP BY [HAVING 條件表示式][WITH ROLLUP];
GROUP BY 關鍵字可以和 GROUP_CONCAT() 函式一起使用。 GROUP_CONCAT() 函式會把每個分組中指定欄位值都顯示出來。同時， GROUP BY 關鍵字通常與集合函式一起使用。集合函式包括 COUNT()/SUM()/AVG()/MAX()/MIN()
SELECT * FROM employee GROUP BY sex;
SELECT sex,GROUP_CONCAT(name) FROM employee GROUP BY sex;
+-----+--------------------+
| sex | GROUP_CONCAT(name) |
+-----+--------------------+
| 女 | 李四 |
| 男 | 張三,王五,Aric |
+-----+--------------------+
SELECT sex,COUNT(sex) FROM employee GROUP BY sex;
SELECT sex,COUNT(sex) FROM employee GROUP BY sex HAVING COUNT(sex)>=3;
SELECT * FROM employee FROM GROUP BY d_id,sex; 先按d_id分組， 再按sex分組
SELECT sex,COUNT(sex) FROM employee GROUP BY sex WITH ROLLUP; WITH ROLLUP 在資料記錄的最後統計一個記錄數總和，跟 COUNT() 連用。
SELECT sex,COUNT(sex) FROM employee GROUP BY sex WITH ROLLUP;
10.2.12 用 LIMIT 限制查詢結果的數量
1.不指定初始位置
eg:
SELECT * FROM employee LIMIT 2; 從初始位置開始，顯示前兩條記錄
SELECT * FROM employee LIMIT 6; 從初始位置開始，顯示前6條記錄，如果不足6條，則顯示有的全部記錄。
2.指定初始位置
SELECT * FROM employee LIMIT 0,2;從初始位置開始，顯示前兩條記錄，"0"代表初始位置
SELECT * FROM employee LIMIT 1,2;從第2條記錄開始，顯示兩條記錄
10.3集合函式查詢
10.3.1 COUNT()
SELECT COUNT(*) FROM employee;
SELECT d_id,COUNT(*) FROM employee GROUP BY d_id;
10.3.2 SUM()函式
SELECT * FROM grade;
SELECT num,SUM(score) FROM grade WHERE num=1001;
10.3.3 AVG()函式
SELECT AVG(age) FROM employee;
SELECT course,AVG(score) FROM grade GROUP BY course;
10.3.4 MAX()函式
SELECT MAX(age) FROM employee;
SELECT course,MAX(score) FROM grade GROUP BY course;
SELECT MAX(name) FROM work;
SELECT MIN(age) FROM age;
SELECT course,MIN(score) FROM grade GROUP BY course;
內連線
SELECT num,name,employee.d_id,age,sex,d_name,function FROM employee,department WHERE employee.d_id=department.d_id;
外連線
①左連線 eg:
SELECT num,name,employee.d_id,age,sex,d_name,function FROM employee LEFT JOIN department ON employee.d_id=department.d_id;
②右連線 eg:
SELECT num,name,employee.d_id,age,sex,d_name,function FROM employee RIGHT JOIN department ON employee.d_id=department.d_id;
10.4.3 複合條件連線查詢
SELECT num,name,employee,d_id,age,sex,d_name,function FROM employee,department WHERE employee.d_id=department.d_id AND age>24;
SELECT num,name,employee,d_id,age,sex,d_name,function FROM employee,department WHERE employee.d_id=department.d_id ORDER BY age ASC;
10.5 子查詢
IN eg:
SELECT * FROM employee WHERE d_id IN(SELECT d_id FROM department);
SELECT * FROM employee WHERE d_id NOT IN(SELECT d_id FROM department);
10.5.2 帶比較運算子的子查詢
CREATE TABLE scholarship(
level INT(4),
score INT(4)
);
INSERT INTO scholarship VALUES
(1,90),
(2,80),
(3,70);
CREATE TABLE computer_stu(
id INT(4)PRIMARY KEY NOT NULL,
name VARCHAR(30) NOT NULL,
score INT(4) NOT NULL
);
INSERT INTO computer_stu VALUES
(1001,'Lily',85),
(1002,'Tom',91),
(1003,'Jim',87),
(1004,'Aric',77),
(1005,'Lucy',65),
(1006,'Andy',99),
(1007,'Ada',85),
(1008,'Jeck',70);
SELECT id,name,score FROM computer_stu WHERE score>=
(SELECT score FROM scholarship WHERE LEVEL=1);
SELECT * FROM employee;
SELECT * FROM department;
SELECT d_id,d_name FROM department WHERE d_id!=
(SELECT d_id FROM employee WHERE age=24);
SELECT d_id,d_name FROM department WHERE d_id<>
(SELECT d_id FROM employee WHERE age=24);
10.5.3 帶 EXISTS 關鍵字的子查詢 內層語句不返回記錄，只返回真假值;當內層語句返回值為真，則進行外層查詢
SELECT * FROM employee;
SELECT * FROM department;
SELECT * FROM employee WHERE EXISTS
(SELECT d_name FROM department WHERE d_id=1003);
SELECT * FROM employee WHERE EXISTS
(SELECT d_name FROM department WHERE d_id=1004);
SELECT * FROM employee WHERE age>24 AND EXISTS
(SELECT d_name FROM department WHERE d_id=1003);
SELECT * FROM employee WHERE NOT EXISTS
(SELECT d_name FROM department WHERE d_id=1003); 因為內層語句返回記錄，故 NOT EXISTS 為假
10.5.4 帶 ANY 關鍵字的子查詢
SELECT * FROM computer_stu;
SELECT * FROM scholarship;
SELECT * FROM computer_stu
WHERE score>=ANY
(SELECT score FROM scholarship);
10.5.5 帶 ALL 關鍵字的子查詢
SELECT * FROM computer_stu WHERE score>=ALL
(SELECT score FROM scholarship);
10.6 合併查詢結果 UNION/ UNION ALL
UNION 將所有查詢結果合併到一起，去除掉相同的
UNION ALL 關鍵字則只是簡單的合併到一起
語句: SELECT 語句1 UNION|UNION ALL SELECT語句2 UNION|UNION ALL SELECT語句n;
SELECT d_id FROM department UNION SELECT d_id FROM employee;
SELECT d_id FROM department UNION ALL SELECT d_id FROM employee;
10.7 位表和欄位取別名
10.7.1 為表取名
SELECT * FROM department d WHERE d.d_id=1001;
10.7.2 為欄位取別名
語句: 屬性名 [AS] 別名
SELECT d_id AS department_id, d_name AS department_name FROM department;
SELECT d.d_id AS department_id,d.d_name AS department_name,d.function,d.address FROM department d WHERE d.d_id=1001;
10.8 使用正則表示式查詢
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