mysql 常用的查询语句

Posted 2020-08-13

 1 1.连接数据库代码:
 2 >mysql -h 主机的ip地址 -u 登入数据库用户名 -p 登入密码
 3 
 4 2.显示数据库
 5 >show databases;
 6 
 7 3.连接数据库
 8 >use dbname;
 9 
10 4.显示当前连接的数据库
11 >select database();
12 
13 5.显示表结构
14 >desc tablename
15 
16 
17 操作表:
18     1.修改表名
19     >alter table table_old rename table_new;
20 
21     2.删除表
22     >drop table tabelname;
23 
24     3.导入数据库
25     >source 文件全路径
26 
27     4.修改字段长度
28     >alter table table_name modify column_name varchar(50) ;
29         4.1.修改字段名称
30     >alter table keyword_info change enabled cate_num varchar(50);
31         4.2.新增表字段名称
32     >alter table keyword_info add enabled varchar(50)
33 
34     5.修改字段类型
35     >alter table talbe_name modify column_name int(12);
36 
37     6.查询建表语句
38     >show create table table_name;
39 
40     7.查询字段去重和统计不重复字段
41     >select distinct(column_name) from table_name;
42     >select count(DISTINCT column_name) from table_name
43 
44     8.删除表字段内容
45     >delete from tablename where  column_name in (‘xx‘,‘xx‘,‘xx‘);
46     >delete from keyword_info where keyword in(‘设计‘,‘新品‘,‘潮牌‘,‘高贵‘);
47 
48     9.查询重复字段
49     >select column_name,count(1) as count from user_table group by column_name having count>1; 
50 
51     10.删除完全重复字段(如果有10000条重复数据我不是要手动执行10000次,通过函数实现循环)
52     >DELETE from keyword_info WHERE keyword in (select keyword from (select keyword,count(1) as count from keyword_info GROUP BY keyword HAVING count>1) as b) LIMIT 1
53 
54     11.更新表字段内容
55     >update table_name SET column_name=新值 WHERE column_name=老值
56 
57     12.查询表插入新表
58     >INSERT INTO talbe1 (cloumn1)  SELECT cloum1_like FROM table2 LIMIT 1;
59     >INSERT INTO keywords_search_info (nick)  SELECT shop_name FROM search LIMIT 1;
60 
61     13.给已有表增加主键
62         1.字段必须不为空
63     >alter table mytable_1 alter column name char(1) not null
64         2.删除原来主键
65     >alter table mytable_1 drop constraint PK_mytable_1（主键名字）
66         3.添加新主键
67     >alter table mytable_1 add constraint PK_mytable_1 primary key(id,name)
68         4.例子
69     >alter table keyword_info add constraint keyword primary key(keyword);
70 
71     14.多表关联(on 后面紧跟主表字段)
72     >select distinct i.shopid from (item i left join task_info t on i.shopid=t.shop_id) left join shop s on i.shopid=s.shop_id where t.type=‘1‘ limit 10,5;
73 
74 高级函数:
75     1.取整
76     >round(x,d)
77 
78     2.求平均
79     >avg(x)
80 
81 一个简单的存储过程:
82 
83 //创建一个存储过程
84 CREATE PROCEDURE p14()
85 
86 BEGIN    
87   DECLARE v INT;    
88   SET v = 0;    
89   WHILE v < 30 DO    
90     DELETE from keyword_info WHERE keyword in (select keyword from (select keyword,count(1) as count from keyword_info GROUP BY keyword HAVING count>1) as b) LIMIT 1;  
91     SET v = v + 1;    
92   END WHILE;    
93 END;
94 
95 
96 CALL p14();//执行这个存储过程
97 
98 drop procedure if exists p4//删除存储过程