linux 中数据库的常用操作

Posted 2020-10-30 SinatJ

1-连接数据库：

 mysql -h localhost -u jiangbiao -p

xxxxx@xxx:~$ mysql -h localhost -u jiangbiao -p
Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 2444832
Server version: 5.5.40-log Source distribution

2-显示表的信息，包括所用引擎，对于mysql，只有InnoDB引擎支持触发器操作

SHOW CREATE TABLE tbl_buniness;

3-显示数据库 : 

show databases;

4-使用数据库：

use databasename;

5-显示数据表：

show tables;

6-显示具体的表结构 :

describe tablename;

7-插入操作：

INSERT INTO `root_trigger` (`id`,`data`)  
VALUES (‘1‘, ‘test root line 1‘),  
       (‘2‘, ‘test root line 2‘),  
       (‘3‘, ‘test root line 3‘);  

8 - 通过DELETE CASCADE外键约束的处理机制来处理级联删除操作：

-- 创建测试主表. ID 是主键.
CREATE TABLE test_main (
  id      INT   NOT NULL,
  value   VARCHAR(10),
  PRIMARY KEY(id)  
);
 
-- 创建测试子表. 
CREATE TABLE test_sub (
  id      INT  NOT NULL,
  main_id INT ,
  value   VARCHAR(10),
  PRIMARY KEY(id)  
);
 
-- 插入测试主表数据.
INSERT INTO test_main(id, value) VALUES (1, ‘ONE‘);
INSERT INTO test_main(id, value) VALUES (2, ‘TWO‘);
 
-- 插入测试子表数据.
INSERT INTO test_sub(id, main_id, value) VALUES (1, 1, ‘ONEONE‘);
INSERT INTO test_sub(id, main_id, value) VALUES (2, 2, ‘TWOTWO‘);

---

--通过  DELETE CASCADE  外键约束的处理机制来处理
mysql> ALTER TABLE test_sub
    ->   ADD CONSTRAINT main_id_cons
    ->   FOREIGN KEY (main_id)
    ->   REFERENCES  test_main(id)
    ->   ON DELETE CASCADE//
Query OK, 2 rows affected (0.16 sec)
Records: 2  Duplicates: 0  Warnings: 0
 
mysql> DELETE FROM
    ->   test_main
    -> WHERE
    ->   id = 1;
    -> //
Query OK, 1 row affected (0.02 sec)
 
mysql> SELECT
    ->   *
    -> FROM
    ->   test_sub;
    -> //
+----+---------+--------+
| id | main_id | value  |
+----+---------+--------+
|  2 |       2 | TWOTWO |
+----+---------+--------+
1 row in set (0.00 sec)

9 - 如果你非要使用触发器来处理， 那么下面是一个例子：

-- 创建测试主表. ID 是主键.
CREATE TABLE t_test_main (
  id      INT   NOT NULL,
  value   VARCHAR(10),
  PRIMARY KEY(id)  
);
 
-- 创建测试子表. 
CREATE TABLE t_test_sub (
  id      INT  NOT NULL,
  main_id INT ,
  value   VARCHAR(10),
  PRIMARY KEY(id)  
);
 
-- 插入测试主表数据.
INSERT INTO t_test_main(id, value) VALUES (1, ‘ONE‘);
INSERT INTO t_test_main(id, value) VALUES (2, ‘TWO‘);
 
-- 插入测试子表数据.
INSERT INTO t_test_sub(id, main_id, value) VALUES (1, 1, ‘ONEONE‘);
INSERT INTO t_test_sub(id, main_id, value) VALUES (2, 2, ‘TWOTWO‘);
 
DELIMITER //
 
CREATE TRIGGER tr_t_test_main_Del
  BEFORE DELETE ON t_test_main
FOR EACH ROW
BEGIN
  DELETE FROM t_test_sub WHERE main_id = OLD.id;
END;
//
 
DELIMITER ;

mysql> delete from  t_test_main  where id = 1;
Query OK, 1 row affected (0.01 sec)
 
mysql> select * from t_test_sub;
+----+---------+--------+
| id | main_id | value  |
+----+---------+--------+
|  2 |       2 | TWOTWO |
+----+---------+--------+
1 row in set (0.00 sec)

关于8、9两点的原文链接：https://zhidao.baidu.com/question/562372469.html

10 - 其他：
这里有个已经整理的博客链接