Data Operation - CRUD
Simple Query
select * from 表名
例：查询所有学生数据
select * from students
adding data
Add a row of data
Formats: all fields set value, the order of columns in the table corresponds to the value of
- Description: growing primary key column is automatically required when inserting placeholder, typically using default or null to zero or placeholder, after successful insertion actual data subject
insert into 表名 values(...)
Example: Insert a student, set all the fields of information
insert into students values(0,'亚瑟',22,177.56)
Format II: part of the field settings, and the order of the fields is given a value corresponding to
insert into 表名(字段1,...) values(值1,...)
Example: Insert a student, setting only the name
insert into students(name) values('老夫子')
Adding multiple rows of data
One way: write multiple insert statements separated by semicolons between statements
insert into students(name) values('老夫子2');
insert into students(name) values('老夫子3');
insert into students values(0,'亚瑟2',23,167.56)
Second way: Write an insert statement, providing a plurality of data, separated by commas between the data
格式一：insert into 表名 values(...),(...)...
例：插入多个学生，设置所有字段的信息
insert into students values(0,'亚瑟3',23,167.56),(0,'亚瑟4',23,167.56)
格式二：insert into 表名(列1,...) values(值1,...),(值1,...)...
例：插入多个学生，只设置姓名
insert into students(name) values('老夫子5'),('老夫子6')
modify
格式：update 表名 set 列1=值1,列2=值2... where 条件
Example: Modify the id student data 5, the name was changed to Di Renjie, age changed to 20
update students set name='狄仁杰',age=20 where id=5
delete
格式：delete from 表名 where 条件
Example: Delete the id data for students 6
delete from students where id=6
Tombstone: For critical data, can not easily execute delete statement delete Once deleted, data can not be restored, then you can logically deleted.
1, add a field to the table, whether the deleted data representing generally named isdelete, 0 represents an deletion represents to delete the default value is 0
2. When you want to delete a data, only need to set this data field is 1 isdelete
3, later in the query data, just check out the isdelete data 0
例：
1、给学生表添加字段(isdelete)，默认值为0，如果表中已经有数据，需要把所有数据的isdelete字段更新为0
update students set isdelete=0
2、删除id为1的学生
update students set isdelete=1 where id=1
3、查询未删除的数据
select * from students where isdelete=0