本文記錄了MySQL的一些常用操作，不多說了，直接一一列出：

/*
Author: liuyazhuang
Date:2016-04-12
*/

use test;
DROP table if exists equipment;
create table equipment(
assetTag INTEGER primary key,
description varchar(20),
acquired Date
);

/*資料表插入語句*/
INSERT INTO equipment values (50431,'21寸監視器', DATE '2013-01-23');
INSERT INTO equipment values (50532,'pad', DATE '2013-01-26');


/*資料表增加新的列，並初始化*/
ALTER Table equipment ADD COLUMN office VARCHAR(20);
UPDATE equipment SET office='Headquarters';

/*向修改後的表中插入記錄*/
INSERT INTO equipment(assetTag,description,acquired) values (50432,'IBM-PC',DATE '2013-01-01');

/*建立代替表的新表（複製）*/
DROP TABLE if EXISTS equipmentMultiSite;
CREATE  TABLE equipmentMultiSite(
assetTag INTEGER PRIMARY KEY,
office varchar(20) DEFAULT 'Headquarters',
description varchar(20),
acquired DATE
);

INSERT INTO equipmentMultiSite
	SELECT assetTag,'Headquarters',description,acquired FROM equipment;


/*刪除現有equipment用檢視代替*/
DROP TABLE equipment;
CREATE VIEW equipment AS
	SELECT assetTag,description,acquired 'dateAcquired',
		FROM equipment WHERE office='Headquarters';
		
		
/*基礎的查詢*/
select sum(amount) from payment where customer_id=1; /*某顧客從開戶以來的消費總額*/
select count(*) from payment where customer_id=1;  /*某顧客從開戶以來的消費次數*/
/*查詢某顧客在2005年5月份和6月份消費總額,用"between”或者"<"，">"來建立條件*/
select sum(amount) from payment where customer_id=1 and extract(year from payment_date)=2005 and extract(month from payment_date) between 05 and 06;
select sum(amount) from payment where customer_id=1 and payment_date >= '2005-05-01 00:00:00' and payment_date < '2005-07-01 00:00:00';
/*下面用法報警了*/
select sum(amount) from payment where customer_id=1 and payment_date > UNIX_TIMESTAMP('2005-05-01 00:00:00') and payment_date < UNIX_TIMESTAMP('2005-07-01 00:00:00');

/*查詢某顧客在2005年一年的總消費*/
select sum(amount) from payment where customer_id=1 and extract(year from payment_date)=2005;
select sum(amount) from payment where customer_id=1 and extract(year from payment_date)='2005'; /*年份加單引號的寫法也能通過，但不夠簡練*/  
/*針對公司，查詢2005年總的銷售額*/
select sum(amount) from payment where extract(year from payment_date)=2005;

/*針對公司，查詢2005年總的銷售額，payment_copy沒有建立索引*/
select sum(amount) from payment_copy where extract(year from payment_date)=2005;

explain select sum(amount) from payment where extract(year from payment_date)=2005;

/*為payment_copy建立索引*/
create index cust_id on payment_copy(customer_id);
/*利用索引提高查詢效率*/
select sum(amount) from payment_copy where customer_id=1 and extract(year from payment_date)=2005;
/*刪除索引*/
drop index cust_id on payment_copy;

create index pay_date on payment(payment_date);
drop index pay_date on payment;


/*建立檢視*/

/*利用檢視查詢*/
select title from film_list;


/*建立臨時表*/
create temporary table if not exists tmp_user(
id integer not null auto_increment COMMENT '使用者ID',
name varchar(20) not null default '' COMMENT '名稱',
sex integer not null default 0 COMMENT '0為男，1為女',
primary key(id)
)engine=MyISAM default charset=utf8 auto_increment=1;


/*顯示臨時表的細節,show table顯示包括table和view但不包括臨時表*/
desc tmp_user;

/*mysql不支援在臨時表上建立檢視，會報錯*/
/*create view v_tmp_user as select * from tmp_user;*/
/*
mysql> create view v_tmp_user as select * from tmp_user;
ERROR 1352 (HY000): View's SELECT refers to a temporary table 'tmp_user'
*/
/*建立預處理語句*/

create view pay_view as
select sum(amount) from payment where extract(year from payment_date)=2005;
/*mysql中連線字串用concat函式，||僅作邏輯運算用*/
create view pay_view as 
	select concat(c.first_name,' ',c.last_name) as name, sum(p.amount) as amount from payment_copy As p,customer As c
    	where extract(year from p.payment_date)=2005 and p.customer_id=c.customer_id group by p.customer_id;			

select * from pay_view;
/*輸出前10條資料*/
select * from pay_view limit 10;
/*輸出第11條到20條資料*/
select * from pay_view limit 11,20;

/*隨機抽取5條資料,order by rand()*/
select * from pay_view order by rand() limit 5;

drop view pay_view;
/*不能給檢視新增索引，只能在基本表上新增索引*/
/*create index pay_view_index on pay_view(amount);*/
/*ERROR 1347 (HY000): 'test.pay_view' is not BASE TABLE*/

/*特別注意：如果檢視和基本表一一對應，檢視的更新可以達到同步修改基本表的目的；如果進行抽取，運算等操作得到檢視，對檢視的操作不能同步到
基本表，檢視中資料和基本表中的資料不一致，檢視中的資料在記憶體中，做臨時顯示使用，有必要時才將資料同步到基本表*/


/*事務，mysql中預設每個sql語句是一個事務，就自動提交一次。考慮到效能，多個語句放在一個事務塊中*/
begin 
drop view pay_view;
create view pay_view as 
	select concat(c.first_name,' ',c.last_name) as name, sum(p.amount) as amount from payment_copy As p,customer As c
    	where extract(year from p.payment_date)=2005 and p.customer_id=c.customer_id group by p.customer_id;			
select * from pay_view limit 10;
end

/*更改表的儲存引擎*/
alert table payment_copy engine=InnoDB;

/*建立mysql定時執行的事件*/
set global event_scheduler=1;
create table testduty(
time varchar(20) default null
)engine=myisam default charset=latin1;

create event if not exists test_event on schedule every 10 second do insert into testduty(time) values(now());


/*刪除定時任務*/
drop event test_event;

/*優化資料表*/
optimize table payment;

/*測試加入索引的效能*/
/*建立兩張表：一個建立索引，另一個不建立*/
create  table  if not exists test_has_index(
id integer not null auto_increment,
num integer not null default 0,
d_num varchar(30) not null default '0',
primary key(id)
)engine=MyISAM default charset=utf8 auto_increment=1;

create table if not exists test_no_index(
id integer not null auto_increment,
num integer not null default 0,
primary key(id)
)engine=MyISAM default charset=utf8 auto_increment=1;

/*建立儲存過程，用於初始化資料表*/
delimiter |
create procedure i_test(pa integer,tab varchar(30))
begin
	declare max_num integer default 10000;
	declare i integer default 0;
	declare rand_num integer;
	declare double_num char;
	
	if tab!='test_no_index'  then
		
		select count(id) into max_num from test_has_index;
		while i < pa do
			if max_num < 10000 then
				select cast(rand()*100 as unsigned) into rand_num;
				select concat(rand_num,rand_num) into double_num;
				insert into test_has_index(num,d_num) values(rand_num,double_num);
			end if;
			set i=i+1;
		end while;
	else	
		select count(id) into max_num from test_no_index;
		while i < pa do
			if max_num < 10000 then
				select cast(rand()*100 as unsigned) into rand_num;
				insert into test_no_index(num) values(rand_num);
			end if;
			set i=i+1;
		end while;
	end if;
end |
	
delimiter ;

/*資料表中記錄較少時，索引反而會影響效能*/
call i_test(10,'test_has_index'); /*call呼叫儲存過程，並傳入引數*/
select num from test_has_index where num!=0;
explain select num from test_has_index where num!=0;
/*Tips: where後的條件，order by ,group by 等這樣過濾時，後面的欄位最好加上索引。根據實際情況，選擇PRIMARY KEY、UNIQUE、INDEX等索引，但是不是越多越好，要適度。*/

select a.num as num1, b.num as num2 
	from test_no_index as a 
		left join test_has_index as b 
			on a.num=b.num;

explain select a.num as num1, b.num as num2 
	from test_no_index as a 
		left join test_has_index as b 
			on a.num=b.num;
/*Tips:資料量特別大的時候，最好不要用聯合查詢，即使你做了索引??*/

/*mysql中使用外來鍵，必須選用innodb儲存引擎，myisam不支援外來鍵*/

/*建立user、order表,二者相關聯,以下也是兩個表關聯的典型例項*/
create table test_user(
id int(10) not null auto_increment COMMENT '使用者ID',
name varchar(20) not null default '' COMMENT '名稱',
sex integer not null default 0 COMMENT '0為男，1為女',
primary key(id)
)engine=innodb default charset=utf8 auto_increment=1;

insert into test_user(name,sex) values("Han",1),("Max",2);

/*建立表test_order,並同步設定了主鍵、索引、外來鍵、儲存引擎innodb*/
create table test_order(
order_id int(10) not null auto_increment comment '訂單ID',
u_id int(10) not null default 0 comment '使用者ID',
username varchar(20) not null default '' comment '使用者名稱',
money int(10) not null default 0 comment '錢數',
datetime timestamp not null default current_timestamp comment '生成時間',
primary key(order_id),
index(u_id),
foreign key order_f_key(u_id) references test_user(id)
)engine=innodb default charset=utf8 auto_increment=1;


/*向order中插入資料*/
insert into test_order(u_id,username,money,datetime) values(1,'Han',223,current_timestamp);
insert into test_order(u_id,username,money,datetime) values(2,'Max',423,current_timestamp);
delete fromm user where id=1;

insert into test_order(u_id,username,money,datetime) values(5,Sophe,223,current_timestamp);

/*外來鍵維護資料完整性的方式有5種
cascade 從父表刪除或更新且自動刪除或更新子表中匹配的行。ON DELETE CASCADE和ON UPDATE CASCADE都可用。
set null 從父表刪除或更新行，並設定子表中的外來鍵列為NULL。ON DELETE SET NULL和ON UPDATE SET NULL子句被支援。
no action InnoDB拒絕對父表的刪除或更新操作。
restrict 拒絕對父表的刪除或更新操作。NO ACTION和RESTRICT都一樣，刪除ON DELETE或ON UPDATE子句。
set default
預設情況下，外來鍵模式是*/
/*查詢test_order表中的外來鍵名稱*/
show create test_order;
/*刪除外來鍵*/
alter table test_order drop foreign key test_order_ibfk_1;

/*新增外來鍵,增加了on delete cascade  on update cascade*/
alter table test_order add foreign key(u_id) references test_user(id) on delete cascade on update cascade;
/*此時更新主表，從表的u_id欄位會自動更改*/
update test_user set id=11 where id=1;

/*下面學習幾個比較使用的mysql函式*/

/*建立新的練習表*/
create table comment(
c_id int(10) not null auto_increment comment '評論ID',
u_id int(10) not null comment '使用者ID',
name varchar(20) not null default '' comment '使用者名稱',
content varchar(1000) not null default '' comment '評論內容',
datetime timestamp not null default current_timestamp,
num1 int(10) default null,
num2 int(10) default null,
primary key(c_id)
)engine=myisam default charset=utf8 auto_increment=1;

/*插入幾條資料*/
insert into comment(u_id,name,content,num1,num2)
	values (1,'test1','3445212',4,23),(2,'test2','up!!',43,21),(3,'test3','a3235b',23,23);

/*greatest(),least()求最值*/
select c_id, greatest(num1,num2) as max, least(num1,num2) as min, num1,num2 from comment
	where num1!="" and num2!="";

/*concat(), concat_ws()用於連線多個字串，CONCAT_WS() 代表 CONCAT With Separator ，是CONCAT()的特殊形式,第一個引數是其它引數的分隔符。間隔符可以自己指定*/
select concat_ws(',',name, content,datetime) from comment;
select concat(',',name, content,datetime) from comment; /*concat會將第一個，當作一個附加的字元*/
select concat(name, ',',content,',',datetime) from comment; /*concat預設不加分隔符，可以手動加入，但不如concat_ws()簡練*/

/*interval（）查詢10小時之前的評論*/
select * from comment where datetime <= (select now()-interval 10 hour as time_start);

/*last_insert_id()查詢最後插入記錄的id*/
select last_insert_id();

/*mysql中可以加入正則匹配查詢*/
select * from comment where content regexp '[A-z][0-9]+';
select * from comment where content regexp '^u';

/*隨機數使用rand()產生，cast（）用於轉換型別*/
select cast(rand()*1000 as unsigned) as rand_num;

/*常用的時間處理函式extract(year from payment_date)=2005或者year(),month(),day(), hour(),minute(),second(),week(), */
select day(now()) as day;
/*上面day（）完全可以代替下面的substring，更簡練*/
select substring(now(),9,2) as day;

/*mysql中分表，大表分成多個小表，提高查詢效能*/
/*利用merge進行分表*/
drop  table if exists  user1;
create table if not exists user1(
id int(10) not null auto_increment,
name varchar(20) not null default '',
sex integer not null default 0,
primary key(id)
)engine=myisam default charset=utf8 auto_increment=1;

drop  table if exists  user2;
create table if not exists user2(
id int(10) not null auto_increment,
name varchar(20) not null default '',
sex integer not null default 0,
primary key(id)
)engine=myisam default charset=utf8 auto_increment=1;

insert into user1(name,sex) values('Alice',0),('Apple',1);
insert into user2(name,sex) values('Bob',1),('Band',0);

/*資料分析筆試題
*/
drop table if exists t1;
create table if not exists t1(
user_id int(10) not null,
blog_id int(10) not null
);
drop table if exists t2;
create table if not exists t2(
blog_id int(10) not null,
comment_id int(10) not null
);

insert into t1 values(1,1),(1,2),(1,3),(2,4),(2,5),(2,6),(2,7),(3,8);
insert into t2 values(2,1),(2,2),(2,3),(2,4),(3,5),(4,6),(4,7),(4,8),(5,9),(5,10);

alter t2 change user_id blog_id int(10);
alter t2 change blog_id comment_id int(10); 

insert into t1 values(1,9),(1,10);
insert into t2 values(9,11),(9,12),(10,13);

alter table t2 change user_id blog_id int(10);
select  t1.user_id,t1.blog_id,t2.comment_id from t1 inner join  t2 on t1.blog_id=t2.blog_id;
select  t1.user_id,t1.blog_id,count(t2.comment_id) from t1 inner join  t2 on t1.blog_id=t2.blog_id 
group by t1.blog_id;
select  t1.user_id,t1.blog_id,count(t2.comment_id) as counts 
	from t1 inner join  t2 on t1.blog_id=t2.blog_id 
	group by t1.blog_id 
	order by counts desc 
	limit 1;
	

/*將上述select的結果插入一個表中*/
drop table if exists t1_t2;
create table if not exists t1_t2(
user_id int(10),
blog_id int(10),
comment_counts int(10)
);

insert into t1_t2 values(2,5,2),(1,9,2),(1,3,1),(1,10,1),(1,2,4),(2,4,3);
/*注意insert into t1_t2表後不加values關鍵詞*/
insert into t1_t2 (select  t1.user_id,t1.blog_id,count(t2.comment_id) as counts 
	from t1 inner join  t2 on t1.blog_id=t2.blog_id 
	group by t1.blog_id 
	order by counts desc);
/*求按user_id分組取最大的2個comment_id對應的blog_id
*下面經過驗證*/


select t.user_id,t.blog_id from t1_t2 t where 2>(select count(*) from t1_t2 
	where user_id=t.user_id and comment_counts>t.comment_counts
		order by t.user_id,t.comment_counts)
			order by t.user_id;
			

	
select  t1.user_id,t1.blog_id from t1 inner join  t2 on t1.blog_id=t2.blog_id order by counts desc;
 group by t1.blog_id ;
 
 select  t1.user_id,t1.blog_id,count(t2.comment_id) as counts 
	from t1 inner join  t2 on t1.blog_id=t2.blog_id 
	group by t1.blog_id 
	having count(t2.comment_id)<=2;
	order by counts desc;
	limit 1;
	
/*
按照blog_id分組取最大的值所在的行
*/



/*將2個表merge成一個表，注意最後一行是engine=merge，而不是type=merge
The older term TYPE is supported as a synonym for ENGINE for backward compatibility,
but ENGINE is the preferred term and TYPE is deprecated. 
*/
/*但是，如下方式直接建立alluser還是報錯了1168：unable to open underlying table which is differently defined or of non-myiasm*/
/*drop  table if exists alluser;
create table if not exists alluser(
id int(10) not null auto_increment,
name varchar(20) default '',
sex integer not null default 0,
index(id)
)engine=MERGE union=(user1,user2) INSERT_METHOD=last AUTO_INCREMENT=1;
*/
/*最後決定採用曲線方式*/
create table alluser like user1;
alter table alluser engine=merge union(user1,user2);
alter table alluser insert_method=last;


desc alluser;
/*從合成的表中查詢*/
select * from alluser;
/*總表中插入記錄*/
insert into alluser(name,sex) values('Merry',1),('Han',0);
select * from user1;
select * from user2;
/*更新總表中記錄*/
update alluser set sex=replace(sex,1,0) where id=2;




/*特別要明白各種關聯查詢,注重查詢效率*/
/*在一個 INNER JOIN 之中，可以巢狀 LEFT JOIN 或 RIGHT JOIN，但是在 LEFT JOIN 或 RIGHT JOIN 中不能巢狀 INNER JOIN。*/
/*INNER JOIN 運算 組合兩個表中的記錄，只要在公共欄位之中有相符的值*/
select a.actor_id,b.film_id from actor as a inner join film_actor as b 
	on a.actor_id = b.actor_id limit 10;

/*兩個表普通連線*/
select a.actor_id,film_id from actor as a, film_actor as b 
	where a.actor_id = b.actor_id limit 10;

	
/*各種查詢關鍵字的順序:
join子句 聯結條件 > where子句 聯結條件和查詢條件 > group by子句分組 > having子句搜尋 >order by子句結果排序 > limit顯示某些記錄
*/


/*連線查詢常用模式*/
/*1、select * from table1, table2 where table1.id=table2.id
2、select * from table1 left join table2 on table1.id = table2.id
3. select * from table1 left join table2 using(id)
4. select * from table1 left join table2 on table1.id=table2.id left join table3 on table2.id=table3.id
5. select * from table1 use index(key1,key2) where key1=1 and key2=2 and key3=3
6. slect * from table1 ignore index(key1) where key1=1 and key2=2 and key3=3
*/
/*驗證各種連線結果,以film, film_actor, actor為例*/
select  f.title,fa.actor from film f left join film_actor fa on f.film_id = fa.film_id limit 10;
select  film.*,film_actor.* from film left join film_actor on film.film_id = film_actor.film_id limit 10;
select  film.title,film_actor.actor_id from film left join film_actor on film.film_id = film_actor.film_id limit 10;
select  film.title,film_actor.actor_id from film left join film_actor using(film_id) limit 10;
select  film.title,film_actor.actor_id from film left join film_actor using(film_id) group by film.film_id limit 10;
select  film.title,film_actor.actor_id from film inner join film_actor on film.film_id = film_actor.film_id limit 10;
/**/
/**/
/**/
	
/*查詢中去掉重複欄位*/
/*建立測試資料表school_report*/
drop  table if exists school_report;
create table school_report(
id int(10) not null auto_increment comment '表ID',
u_id int(10) not null comment '學生ID',
name varchar(20) not null default '' comment '學生姓名',
score varchar(4) not null default 0 comment '學生成績',
message varchar(50) not null default '',
dateline timestamp not null default current_timestamp,
primary key(id)
)engine=innodb default charset=utf8 auto_increment=1;


/*插入測試資料*/
insert into school_report(u_id,name,score,message)
	values(1,'張三',89,'helloworld'),(1,'張三',90,'hello'),(2,'李四',92,'helloworld'),
		(3,'王五',93,'world');

/*查詢，去掉重複*/
select distinct name,score from school_report;
select *, count(distinct name) from school_report group by name;
/**/
select * 
	from school_report a inner join( 
		select max(dateline) as dateline 
			from school_report group by u_id) b
				on a.dateline = b.dateline
					group by id order by a.dateline desc;



/*記錄和分析 花費時間較多的select*/

/*首先進行如下設定，設定long_query_time時間限*/
show variables like "%long%";
set global long_query_time=2;

/*檢查並開啟慢查詢,會顯示mysql-slow.log檔案的路徑*/
show variables like "%slow%";
set global slow_query_log='ON';

/*這樣超過long_query_time的查詢會記錄到mysql日誌中*/

/*分組後前n條資料: http://www.jb51.net/article/31590.htm*/
drop  table if exists tb;
create table tb (
name varchar(10),
val int,
memo varchar(20)
);

insert into tb values('a', 2, 'a2(a的第二個值)'),('a',1,'a1--a第一個值'),
('a',3,'a3--a第三個值'),('b',1,'b1--b第一個值'),('b',3,'b3--b第三個值'),
('b',2,'b3--b2b2b2'),('b',4,'b4b4b4'),('b',5,'b5b5b5b5');

/*按name分組取value 最大的值的記錄*/

--方法1：select a.* from tb a where val = (select max(val) from tb where name = a.name) order by a.name 
--方法2： 
select a.* from tb a where not exists(select 1 from tb where name = a.name and val > a.val); 
--方法3： 
select a.* from tb a,(select name,max(val) val from tb group by name) b where a.name = b.name and a.val = b.val order by a.name; 
--方法4： 
select a.* from tb a inner join (select name , max(val) val from tb group by name) b on a.name = b.name and a.val = b.val order by a.name ;
--方法5 
select a.* from tb a where 1 > (select count(*) from tb where name = a.name and val > a.val ) order by a.name ;
/* 
name val memo 
---------- ----------- -------------------- 
a 3 a3:a的第三個值 
b 5 b5b5b5b5b5 

方法三、四效率比較高
*/ 

/*按name分組取val最小的值的記錄*/

--方法1：select a.* from tb a where val = (select min(val) from tb where name = a.name) order by a.name 
--方法2： 
select a.* from tb a where not exists(select 1 from tb where name = a.name and val < a.val); 
--方法3： 
select a.* from tb a,(select name,min(val) val from tb group by name) b where a.name = b.name and a.val = b.val order by a.name ;
--方法4： 
select a.* from tb a inner join (select name , min(val) val from tb group by name) b on a.name = b.name and a.val = b.val order by a.name ;
--方法5 
select a.* from tb a where 1 > (select count(*) from tb where name = a.name and val < a.val) order by a.name ;
/* 
name val memo 
---------- ----------- -------------------- 
a 1 a1--a的第一個值 
b 1 b1--b的第一個值 

*/ 
/*按name分組取出第一次出現的記錄*/

select a.* from tb a where val = (select top 1 val from tb where name = a.name) order by a.name 
/* 
name val memo 
---------- ----------- -------------------- 
a 2 a2(a的第二個值) 
b 1 b1--b的第一個值 
*/
 
/*按name分組隨機取一條資料*/

select a.* from tb a where val = (select top 1 val from tb where name = a.name order by newid()) order by a.name/* 
name val memo 
---------- ----------- -------------------- 
a 1 a1--a的第一個值 
b 5 b5b5b5b5b5 

*/ 
/*按name分組取最小的2個（N個）val所在記錄*/

select a.* from tb a where 2 > (select count(*) from tb where name = a.name and val < a.val ) order by a.name,a.valselect a.* from tb a where val in (select top 2 val from tb where name=a.name order by val) order by a.name,a.val 
select a.* from tb a where exists (select count(*) from tb where name = a.name and val < a.val having Count(*) < 2) order by a.name 
/* 
name val memo 
---------- ----------- -------------------- 
a 1 a1--a的第一個值 
a 2 a2(a的第二個值) 
b 1 b1--b的第一個值 
b 2 b2b2b2b2 

*/ 
/*按name分組取最大的2個（N個）val所在記錄*/

select a.* from tb a where 2 > (select count(*) from tb where name = a.name and val > a.val ) order by a.name,a.val 
select a.* from tb a where val in (select top 2 val from tb where name=a.name order by val desc) order by a.name,a.val 
select a.* from tb a where exists (select count(*) from tb where name = a.name and val > a.val having Count(*) < 2) order by a.name 
/* 
name val memo 
---------- ----------- -------------------- 
a 2 a2(a的第二個值) 
a 3 a3:a的第三個值 
b 4 b4b4 
b 5 b5b5b5b5b5 
*/ 
/*MySQL中序列有auto_increment，Oracle中使用sequence序列和**.NextVal*/
/*在Oracle中可以新增觸發器，實現mysql形式的自增長；mysql也可以通過定義過程實現Oracle的序列語法*/
/*mysql實現currval()*/
drop table if exists sequence;
create table sequence(
name varchar(50) not null,
current_value int not null,
increment int not null default 1,
primary key(name)
)engine=InnoDB;

insert into sequence values('MovieSeq',3,5);

Drop function if exists currval;
delimiter $
create function currval(seq_name varchar(50))
returns integer
contains sql
begin
	declare value integer;
	set value=0;
	select current_value into value
	from sequence
	where name=seq_name;
	return value;
end$
delimiter ;
/*測試定義的currval*/
select currval('MovieSeq');

/*mysql實現nextval()*/
drop function if exists nextval;
delimiter $
create function nextval(seq_name varchar(50))
returns integer
contains sql
begin 
	update sequence
	set	current_value=current_value+increment
	where name=seq_name;
	return currval(seq_name);
end$
delimiter ;

/*測試定義的nextval()*/
select nextval('MovieSeq');
select nextval('MovieSeq');

/*mysql實現setval(). 報錯了！！*/
drop function if exists setval;
delimiter $
create function setval(seq_name varchar(50),val integer)
returns integer
contains sql
begin
	update sequence
	set current_value=val;
	where name = seq_name;
	return currval(seq_name);
end$
delimiter ;

/*測試定義的setval()*/
select setval('MovieSeq',150);
select curval('MovieSeq');
select nextval('MovieSeq');

/*即作為主鍵同時又是外來鍵的情況*/
drop table if exists Issues;
create table Issues (
issue_id integer auto_increment primary key
);

drop table if exists Bugs;
create table Bugs(
issue_id integer primary key,
foreign key(issue_id) references Issues(issue_id)
);

insert into Issues values();
insert into Issues values();
select * from Issues; /*1,2*/
select * from Bugs; /*null*/
insert into Bugs values(4); /*報外來鍵引用錯誤*/
insert into Bugs values(2); /*正常插入，只要插入Issues中存在的資料就OK*/
select * from Bugs; /*2*/



/*浮點數的表示*/

/*浮點數不能比較，要用近似相等*/
drop table if exists Num;
create table Num(
id integer auto_increment primary key,
price float not null default '0.0',
sum float not null default '0.0',
);

/*float型別的資料儲存時滿足IEEE754二進位制浮點數的標準，表達的範圍很大，舍入方式不是四捨五入；
當儲存的值在Integer和numeric型別所支援的範圍內，就不必選擇float型別。推薦用numeric*/

alter table Num add column price2 numeric(9,2) default '0.0';
/*numeric(9,2)定義的price2列儲存的就有2位小數位，可以進行=精確比較，即使插入了3個小數位，會四捨五入*/


/*限定列的有效值：
如果，可選範圍固定，使用Enum和Check約束,check約束使用範圍更廣，如檢查start永遠小於end；
否則，將可選資料建立一個檢查表*/
drop table if exists PersonalContacts;
Create table PersonalContacts(
id integer auto_increment primary key,
salutation varchar(5) check (salutation in ('Mr.','Mrs.','Ms.','Dr.'))
);

drop table if exists PersonalContacts;
Create table PersonalContacts(
id integer auto_increment primary key,
salutation enum('Mr.','Mrs.','Ms.','Dr.')
);
/*用Enum限定列的取值範圍，插入不屬於其範圍的值時，未報錯但插入欄位為空。插入範圍內的值，一切正常*/
insert into PersonalContacts(salutation) values('Mz.');
select * from PersonalContacts;

insert into PersonalContacts(salutation) values('Ms.');
select * from PersonalContacts;
/*注：enum是mysql獨有的特性*/

/*要想增加某列取值範圍，需要更改資料表，ETL（抽取--》轉換--》載入資料）,但麻煩*/
alter table PersonalContacts modify column salutation enum('Mr.','Mrs.','Ms.','Dr.','Mz.');
 
insert into PersonalContacts(salutation) values('Mz.');
select * from PersonalContacts;

/*可選資料建立一個檢查表*/
drop table if exists Salutation;
create table Salutation(
status varchar(5) primary key
);

insert into Salutation(status) values('Mr.','Ms.');

drop table if exists PersonalContacts2;
/*定義外來鍵時，加上on update cascade，重新命名一個值就比較方便*/
create table PersonalContact2(
id integer auto_increment primary key,
status varchar(5),
foreign key(status) references Salutation(status) on update cascade  
);
/*方便查詢、插入和更改*/
select status from Salutation order by status;
insert into Salutation(status) values('Mss.');
update Salutation set status='Dr.' where status='Mss'; 

/*使用檢查表，支援廢棄資料(保持歷史資料的值，對新插入的數值加限制)*/
alter table Salutation add column active enum('inactive','active') not null default 'active';

/*使用update代替delete廢棄一個值*/
update Salutation set active='inactive' where status='Dr.';
select status from Salutation where active='active';


/*mysql資料型別：
1.數值型別

MYSQL支援所有標準SQL,這其中包括:

    精確數值資料型別:INTERGER/INT,SMALLINT,DECIMAL/DEC,NUMERIC
    近似數值資料型別:FLOAT,REAL,DOCULE PRECISION
    BIT資料型別
作為對標準SQL的擴充套件,MySQL還支援TINYINT,MEDIUMINT及BIGINT


    如果ZEROFILL指定給數值列,則MYSQL會自動新增UNSIGNED屬性
    整數或浮點型別均可指定AUTO_INCREMENT屬性,當被賦值NULL或0時會自動設定成下一個序列值,AUTO_INCREMENT序列從1開始
    MYSQL將DOUBLE與DOUBLE PRECISION等同,將REAL也與DOUBLE PRECISION等同
    DECIMAL與NUMERIC用來儲存精確數值資料,NUMERIC是DECIMAL的一種實現,MYSQL5.5將DECIMAL與NUMERIC儲存為二進位制格式
    BIT資料型別用來儲存位元數值,BIT(M)中M允許從1到64,位數不足時會自動左側補0
    SERIAL 等同於BIGINT UNSIGNED NOT NULL AUTO_INCREMENT UNIQUE

 2.日期時間型別
     當使用DATE與TIME型別時通常需要注意的事項：

     MYSQL會嘗試從各種格式的輸入中解析日期與時間，但還是有格式限制的
    只有兩位數的YEAR，會讓MYSQL感到迷惑，所以MYSQL會嘗試作下面的解析：在70～99之間的年會被解析成：1970～1999，在00～69之間的年會被解析成2000～2069
    MYSQL在解析日期時，日期的輸入順序必須為：year-month-day,否則無法正確解析
    預設情況下，MYSQL會將超出範圍或不合法的日期與時間，轉換成0，但對於超出範圍的TIME，會將其歸整到一個恰當的時間點上。
 
 3.字串型別
    字串型別包括:CHAR,VARCHAR,BINARY,VARBINARY,BLOB,TEXT,ENUM和SET. 


	*/

/*圖片等多媒體資訊儲存在資料庫內，還是儲存在資料庫外（檔案系統中）*/
/*儲存在資料庫外（僅用varchar存放圖片檔案路徑）
缺點：
1. 不支援delete
2. 不支援事物隔離
3. 不支援回滾
4. 檔案不支援資料庫備份工具
5. 不支援訪問許可權限制
6. 檔案不是SQL資料型別*/

/*儲存在資料庫內（使用Blob型別）
優點：解決 儲存在資料外 的6個缺點
Blob 初始化 可以從檔案中匯入；
Blob 內容 也可以匯入檔案中。

缺點：需要資料表佔用空間更大，備份更大
*/
drop table  if exists Bugs;
create table Bugs(
bug_id integer auto_increment primary key
);
/*image_id integer auto_increment not null,*/

drop table if exists Screenshots;
/*SERIAL 等同於BIGINT UNSIGNED NOT NULL AUTO_INCREMENT UNIQUE*/
create table Screenshots(
bug_id integer not null,
image_id serial not null,
screenshot_image BLOB,
caption varchar(100),
primary key (bug_id,image_id),
foreign key (bug_id) references Bugs(bug_id)
);

/*如果採用 記錄路徑名的 方式，儲存在資料庫之外的檔案系統中*/
/*
create table Screenshots(
bug_id integer not null,
image_id serial not null,
screenshot_path varchar(100),
caption varchar(100),
primary key (bug_id,image_id),
foreign key (bug_id) references Bugs(bug_id)
);
*/

/*插入資料*/
insert into Bugs values();
insert into Bugs values();
insert into Bugs values();
insert into Bugs values();
insert into Bugs values();
insert into Bugs values();

/*初始化Blob資料型別*/
insert into Screenshots(bug_id,screenshot_image) values(1,load_file('f:\aaa.jpg')); 
/*這裡插入時，必須指明bug_id*/

select bug_id,image_id from Screenshots;
/*驗證發現image_id是自增的*/

select screen_image from Screenshots;
/*會顯示出一大片的圖片二進位制字元*/

insert into Screenshots(bug_id,screenshot_image) values(1,load_file('f:\bbb.jpg'));
insert into Screenshots(bug_id,screenshot_image) values(2,load_file('f:\ccc.jpg'));

delete from Screenshots where bug_id=1 and image_id=3;

/*將資料庫中儲存的Blob圖片，匯出到檔案系統*/
select screenshot_image into dumpfile 'F:\aaa111.jpg'
from Screenshots
where bug_id=1 and image_id=2;
/*問題：生成了 檔名 是aaa111的檔案，但是開啟只顯示沒有預覽1B???????????原圖片249kb*/

select screenshot_image into dumpfile 'F:\\aaa222.jpg'
from Screenshots
where bug_id=1 and image_id=2;

/*索引：在SQL標準中沒有很多的說明，不同資料庫實現有較大的自由度和區別*/

/*合理地使用索引!!!!
錯誤的觀點：
1. 不使用索引或索引不足
2. 使用太多的索引
3. 執行一些讓索引無能為力的查詢

1. 要根據具體情況，分析需要建立哪些索引，在維護索引的開銷 和 索引帶來的加速之間進行比較
2. 通過mentor方法： measure(慢查詢)，解釋（explain),挑選，效能測試，優化，重建（定期維護：analyze table or optimize table）

注意：
1. insert update delete都要維護索引
2. 索引可以快速找到要delete或update的記錄
3. 主鍵會自動建立索引，沒有必要手工加入
4. 對於過長的varchar不建議建立索引，不太可能進行全匹配查詢
5. 可以根據實際需求建立組合索引*/
drop table if exists Bugs1;
create table Bugs1(
bug_id serial primary key,
date_reported date not null,
summary varchar(80) not null,
status varchar(10) not null,
hours numeric(9,2),
index(bug_id,date_reported,status)
);

/*考慮：bugs與多個標籤的關係（多個標籤不互斥）*/
/*一個 bugs對應的最多標籤數確定時，可以採用建立多個tage列,但在查詢、新增和刪除tag都很方便*/
/*一個 bugs對應的最多標籤數確定時，強烈建議使用 從屬表，僅使用一列儲存【多值屬性】，多個值儲存在多行，而不是多列！
從表中定義外來鍵和主記錄關聯*/

drop table if exists Tags;
create table Tags(
bug_id integer not null,
tag varchar(20),
primary key(bug_id,tag),
foreign key(bug_id) references Bugs(bug_id)
);

insert into Tags(bug_id,tag) values('1','crash'),('2','performance'),('2','printing'),('2','crash'),(3,'printing');
select * from Tags where bug_id=2;

/*查詢和 某標籤 相關的所有bug*/
select * from Bugs join Tags using(bug_id) where tag='performance';

/*查詢和 某2個標籤 相關的所有bug記錄*/
select * from Bugs 
join Tags as t1 using (bug_id)
join Tags as t2 using (bug_id)
where t1.tag='printing' and t2.tag='performance';
/*結果：
+--------+----------+-------------+
| bug_id | tag      | tag         |
+--------+----------+-------------+
|      2 | printing | performance |
+--------+----------+-------------+
*/


/*使用從屬表 可以更方便地 新增和移除 bugs和tag標籤之間的關係*/
insert into Tags(bug_id,tag) values (3,'save');
delete from Tags where bug_id=2 and tag='crash';

/**/

/**/