MySQL basic addition, deletion, modification and query of SQL statements

CRUD

Insert sentence

insert into `good` (id,good_name,price) values(11,' Apple mobile phone ',5000);
--  Table name   Name   Name   Name   value 

• insert Statement notes
  • The inserted data should be of the same data type as the field
  • The length of the data should be within the specified range , for example ： One length cannot be 80 The string of is added to the length of 40 In the column of
  • stay values The data positions listed in must correspond to the arrangement positions of the added columns
  • Character and date type data should be enclosed in single quotation marks
  • Columns can be inserted with null values 【 Provided that this field is allowed to be empty 】
  • insert into tab_name ( Name …) values(),(),()…;
  • If you are adding data to all fields in the table , You may not write the field name in front
  • Use of default values , When a field value is not given , If there is a default value, it will be added , Otherwise, the report will be wrong .

update sentence

update good set price = price + 1000 where good_name = ' Apple mobile phone ';

• Use details
  • update Syntax to update columns in the original table row with new values .
  • set Clause indicates which columns to modify and which values to assign .
  • where Clause specifies which rows should be updated , If not where Clause , Update all rows （ Record ）
  • If you need to modify multiple fields , Can pass set Field 1 = value 1, Field 2 = value 2…

delete sentence

delete from good where good_name = ' Apple mobile phone ';

• Use details
  • If not applicable where Clause , All data in the table will be deleted
  • Delete Statement cannot delete the value of a column （ You can use update Set to null perhaps ‘’）
  • Use delete Statement only delete records , Don't delete the table itself . If you want to delete a table , Use drop table sentence .

select sentence

Basic grammar

select [distinct] *|{column1,column2,....} from table_name;

• matters needing attention
  • select Specify which columns of data to query
  • column Specifies the column name
  • * Number means to query all columns
  • from Specify which table to query
  • distinct Optional , It refers to the time of query results , Whether to remove duplicate data

--  Count the total score of each student 
select `name`,(chinese+english+math) from student;
--  Add 10 branch 
select `name`,(chinese+english+math+10) from student; 
--  Use an alias to represent the student's total score 
select `name` as ' name ',(chinese+english+math) as total_score from student;

where Operators often used in

• Comparison operator

  > < <= >= = <> !=  --  Greater than , Less than , Greater than （ Less than ） be equal to , It's not equal to 
  

  between ... and ... --  The value displayed in an area 
  

  in(set) --  Displayed in the in Values in the list , for example ,in(100,200)  This set It's a collection , Does not mean interval 
  

  like ' Zhang pattern'
  not like ''  --  Fuzzy query 
  

  is null --  Determine whether it is null 
  

• Logical operators

  and --  Multiple conditions hold at the same time 
  or --  Any of several conditions holds 
  not --  Don't set up , for example ：where not (salary>100);
  

select * from student where (chinese+english+math) > 200 and math< chinese and `name` like ' Han %';

--  This   Han %  Indicates a string beginning with Han , No matter how many characters there are after Han .
--  Han _  Indicates a string beginning with Han , however   There can only be one character after Han .

• between …and…( Closed interval )

select * from student where english between 80 and 90;

Use order by Clause sort query results

select column1,column2,... from tablename order by column asc|desc;

• order by Specify sorted columns , The sorted column can be either the column name in the table , It can also be select The column name specified after the statement
• asc Ascending 【 Default 】,desc Descending
• order by Clause should be in select End of statement

select * from student order by math;--  The default is ascending 
select * from student order by math desc --  according to math Grades in descending order 
select `name`,(chinese+math+english) as total_score from student order by total_score;
--  Arrange the total scores in ascending order 
select `name`,(chinese+math+english) as total_score from student order by total_score desc;
--  Arrange the total scores in descending order