mysql中各類複雜的增刪改查

1.mysql查出數據表中連續出現三次或三次以上的數據

建一張表以下：表名爲 number

1.1 要求找出num列連續出現三次或三次以上的數據：

select * from number where id in (
    select distinct n1.id from number n1,number n2,number n3
    where (n1.num = n2.num and n2.num = n3.num and ( 
         (n1.id + 1= n2.id  and n2.id +1 = n3.id)or
         (n3.id + 1= n2.id  and n2.id +1 = n1.id)or
         (n3.id + 1= n1.id  and n1.id +1 = n2.id)
      )
    ) 
order by n1.id )

 

運行結果：

 

1.2找出上表（運行結果表）中重複數據中id最小的數據。

思想：將上表中的數據分組取最小。

select min(id) as minid,id,num
from ((select * from number where id in (
    select distinct n1.id from number n1,number n2,number n3
    where (n1.num = n2.num and n2.num = n3.num and ( 
         (n1.id + 1= n2.id  and n2.id +1 = n3.id)or
         (n3.id + 1= n2.id  and n2.id +1 = n1.id)or
         (n3.id + 1= n1.id  and n1.id +1 = n2.id)
      )
    ) 
order by n1.id ))as t) group by num ;

 

運行結果：

2.刪除表中的重複數據，保留id最小的數據

原表中的數據以下：

/*
    方法一：
        1.建立臨時表
        2.將須要的數據保存到臨時表
        3.清空原表，將臨時表中的數據保存到原表中
        4.刪除臨時表
*/
    create temporary table temp

    select min(id),email from test group  by email;

    truncate table test;

    insert into test select * from temp;

    select * from test;

    drop table temp;

/*
  方法二：
        1.按照郵件分組，把每一組中的最小的id取出放在臨時表中
        
        2.刪除原表中除臨時表中id之外的其餘id 對應的數據
*/

    create temporary table temp

    select min(id) as minid from test group by email;  

    delete from test where id not in (select minid from temp);

    drop table temp;

/*
  方法三：
       在原表上操做
*/
   delete from test where id not in (
       select minid from (
          select min(id) minid from test group by email
         )b
     );
     select * from test;

運行結果：

3.mysql中的各類鏈接

建立兩張表，表明兩個店鋪，每一個店鋪有不一樣的，每一個櫃檯賣不一樣的商品。

/*
   兩個商店，每一個店有不一樣的櫃檯，每一個櫃檯上賣有不一樣的商品
*/
create table tableA(
    id int(10) not null primary key auto_increment,
        monorail varchar(20),
        variety varchar(50)
);
insert into tableA 
values (1,'a1','蘋果'),(2,'a1','梨'),(3,'a3','香蕉'),(4,'a4','蘋果'),(5,'a5','西瓜'),
(6,'a6','蘋果'),(7,'a7','葡萄'),(8,'a8','桃子');
create table tableB(
    id int(10) not null primary key auto_increment,
        monorail varchar(20),
        variety varchar(50)
);
insert into tableB 
values (1,'b1','蝦'),(2,'b2','豬肉'),(3,'b3','蘋果'),(4,'b4','西瓜'),(5,'b5','梨'),
(6,'b6','香蕉');

兩個表數據以下：

 

’

3.1.內鏈接

/*
  內鏈接，查處兩個商店共有的商品
*/
select * from tablea A INNER  JOIN tableb B
on A.variety = B.variety ;

 運行結果

 

3.2.左鏈接

/*
  左鏈接，以A表爲左表
*/
select * from tablea A LEFT  JOIN tableb B
on A.variety = B.variety ;

運行結果

3.3.右鏈接

/*
  右鏈接，以A表爲左表
*/
select * from tablea A RIGHT  JOIN tableb B
on A.variety = B.variety ;

運行結果

 

3.4.左外鏈接

/*
  左外鏈接，以A表爲左表
*/
select * from tablea A LEFT  JOIN tableb B
on A.variety = B.variety Where B.variety is null;

運行結果

3.5.右外鏈接

/*
  右外鏈接，以A表爲左表
*/
select * from tablea A RIGHT  JOIN tableb B
on A.variety = B.variety Where A.variety is null;

運行結果

3.6.全鏈接  

mysql不支持full  (outer) join 故使用union代替

/*
  全鏈接
*/
select * from tablea A LEFT  JOIN tableb B
on A.variety = B.variety ;
union
select * from tablea A RIGHT  JOIN tableb B
on A.variety = B.variety ;

運行結果

3.7.全外鏈接

select * from tablea A LEFT  JOIN tableb B
on A.variety = B.variety Where B.variety is  null 
union
select * from tablea A RIGHT  JOIN tableb B
on A.variety = B.variety Where A.variety is  null

運行結果

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