Adding, deleting, modifying and querying MySQL tables (basic)

1、 newly added （Create）

1.1、insert insert data

Create database

Specify database
Create table

See the table

View table structure

Insert code :
insert into Table name values ( The value of the column …);

Query table

1.11、 requirement values() The number of fields in the header, the number of columns agreed in the header, and the type of each column , To match

matching

1.12、 stay SQL To represent a string in , Both English and Chinese formats are acceptable ’ ’ , ‘’ ‘’

‘ This one can ’ “ This one is OK ”

1.13、 If a column is datetime( Time stamp ), How to match

1) Insert a specified time by specifying a format string
2) adopt now() Function to insert a Current system time
First of all, this table is in student in

Specify time :

system time :

Query table ( Traverse ?):

1.14、insert During insertion , You can insert only one column or several columns , At this point, the other columns will adopt the default settings

1) Insert a column

2) Insert some columns

1.15、 Chinese can also be inserted

MySQL The default encoding is Latin

The configuration scheme is in the notes

1.16、 Insert more than one line at a time

2、 Look for statements select

2.1、 Full column lookup

The most basic search , Full column lookup , Put all the columns of a table directly , And all the rows
select * from Table name ;
insert data :

Example full column lookup :

What you find here is a temporary table
All the tables in the database are on the hard disk But here in memory Release after output

2.2、 Specified column query

select Name … from Table name :

This query is more efficient
Targeted queries
The query here is also a temporary table " Release at any time "------> Release after printing

2.3、 Specifies that the query field is an expression

Queries are accompanied by operations

Now query Chinese scores are ten more than usual
It's also a temporary table

Three grades and

2.4、 Specify alias for query field

It is equivalent to a temporary table for query , New column names have been developed

It's easy to get confused

2.5、 De duplication of query results distinct

For query results , Remove duplicate data



The weight cannot be removed at this time

2.6、 Sort

For query results ( A temporary table ) Sort
select Name … from Table name order by Name asc/desc;
Descending

Default ascending order For math scores

asc Ascending

Sorting empty values is considered the minimum value

Sorting can also depend on expressions or aliases

Sort by alias

It can also be used. order by Sort multiple columns
Now sort according to the first column , If the first column is the same , Then the next column , And so on

2.7、select Conditional queries in

select Heel where+ Specific screening conditions
select Name from indicate where Conditions ;

where The following condition has nothing to do with the preceding column

where Words and sentences cannot use aliases



The expression also has and and or that and first

Cao mengde is not satisfied and

between------ Section

What's the math score () Any value in can be queried — Fixed value query


It can also be done through or To achieve the same purpose

The use of wildcards

2.8、 Paging query

Yes 8 That's ok

We can set the number of search results on any page ( That's ok )

select * from exam_result limit Number of lines per page ;

select * from exam_result limit 3 offset 3;
select * from exam_result limit 3 offset Start with the line ;

3、MySQL Modification operation of

3.1、 Definition update operation

update exam_result set math = ‘80’ where name = ‘ The Monkey King ’;

3.2、 Screening operations limit

Top three filters

Add and modify operations



Revise the Chinese score to the original one 1/2

4、 Delete operation delect

delete from exam_result where id = 8;