MySQL study notes: Implementation methods of adding, deleting and modifying data_MySQL

The example in this article describes the implementation method of adding, deleting and modifying data in MySQL study notes. Share it with everyone for your reference, the details are as follows:

1. Add data

Insert code format:

insert into indicates [column name…] values ​​(value…)

create table test21(name varchar(32));
insert into test21 (name) values ('huangbiao');

Insertion principle:

1. The inserted data should be of the same data type as the field
2. The size of the data should be within the specified range of the column
3. The data position listed in values ​​must correspond to the arrangement position of the added column

Example:

create table test22(id int,name varchar(32));
mysql> insert into test22 (id,name) values (3,'huangbiao');
mysql> insert into test22 (name,id) values ('huangbiao2',5);
mysql> insert into test22 (name,id) values ('',51);
mysql> insert into test22 (name,id) values (NULL,555);
mysql> insert into test22 (id) values (15);

2. Update data

Updated data syntax format:

update indicates set column name = expression … where condition

Note: If there is no condition after where, it is equivalent to operating on the entire table.

Example data:

create table employee(
   id int,
   name varchar(20),
   sex bit,
   birthday date,
   salary float,
   entry_date date,
   resume text
);
insert into employee values(1,'aaa',0,'1977-11-11',56.8,now(),'hello word');
insert into employee values(2,'bbb',0,'1977-11-11',57.8,now(),'hello word');
insert into employee values(3,'ccc',0,'1977-11-11',56.3,now(),'hello word');

Change all the sal fields of the employee table to 2000

update employee set sal=2000;

Set the sal field of the user named zs to 3000

update employee set sal=3000 where name='zs'

Add 100 to the original sal field of the user named wu

update employee set sal=sal+100 where name='wu'

3. Delete data

Delete data syntax:

delete from indicates where condition

Principles for deleting data:

1. If you do not use the where clause, all data in the table will be deleted
2. The delete statement cannot delete the value of a certain column (you can use update)
3. Delete only deletes records, not the table itself. If you want to delete a table, use the drop table statement
4. Like insert and update, deleting a record from one table will cause referential integrity problems in other tables
5. You can also use the truncate table statement to delete data in the table

mysql transaction

1. The mysql console automatically submits transactions (dml) by default
2. If we want to use transactions in the console, please see below:

mysql deleted data is automatically submitted

mysql> set autocommit=false;
Query OK, 0 rows affected (0.00 sec)
mysql> savepoint aaa;
Query OK, 0 rows affected (0.00 sec)
mysql> delete from employee;
Query OK, 3 rows affected (0.05 sec)
mysql> select * from employee;
Empty set (0.00 sec)
mysql> rollback to aaa;
Query OK, 0 rows affected (0.06 sec)
mysql> select * from employee;
+------+------+------+------------+--------+------------+------------+
| id  | name | sex | birthday  | salary | entry_date | resume   |
+------+------+------+------------+--------+------------+------------+
|  1 | aaa |   | 1977-11-11 |  56.8 | 2014-11-10 | hello word |
|  2 | bbb |   | 1977-11-11 |  57.8 | 2014-11-10 | hello word |
|  3 | ccc |   | 1977-11-11 |  56.3 | 2014-11-10 | hello word |
+------+------+------+------------+--------+------------+------------+
3 rows in set (0.00 sec)

Readers who are interested in more MySQL-related content can check out the special topics on this site: "Summary of MySQL Index Operation Skills", "Comprehensive Collection of MySQL Log Operation Skills", "Summary of MySQL Transaction Operation Skills", "Comprehensive Collection of MySQL Stored Procedure Skills", " Summary of MySQL database lock related skills" and "Summary of commonly used MySQL functions"

I hope this article will be helpful to everyone’s MySQL database planning.