Basic syntax of MySQL DDL and DML and DQL

SQL Sentence classification ：

One 、DDL（ Data definition language ）

        explain ： Define and manage data objects , Such as a database , Data sheets, etc .

        command ：create、drop、alter

  Basic grammar ：

          Operation of the library ：

                  Show all libraries ：show  database;

                  Create a library ：create  database Library name ;

                  Delete a library ：drop database Library name ;

                  Use the library ：use Library name ;

          The operation of the table ：

                  Look at all the tables in the library ：show tables;

                  Build table ： create table Table name （

                                  Field name type attribute Indexes notes ,

                                   Field name type attribute Indexes notes ,

                                  ...

                                   Field name type attribute Indexes notes

                            ）;

                  View table structure ：desc Table name ;

                                         show create table Table name ;

                  Storage engine ：ENGING=InnoDB

                  Modify and delete database tables ：

                                 Modify the name of the table ：alter table The old name of the table rename as The new name of the table

                                 Modify fields ：alter table Table name modify Field name type attribute

                                alter table Table name change Old field name new field name type attribute

                                 Add fields ：alter table Table name add Field name type attribute

                                 Delete field ( Dangerous operation )：alter table Table name drop Field name

                                 Delete table ( Dangerous operation )：alter table Table name

                  Add constraints ：                          

                                 Add non empty constraints ：alter table Table name modify test_student char(10) not null; Delete non empty constraints

                                 Add unique constraints ：alter table Table name add unique( Table field name , Field , Field , Field );

                                 Add primary key constraint ：alter table Table name add primary key( The field name of the table , Field , Field );

                                 Add a foreign key constraint ：alter table Table name add constraint N1 foreign key ( Table field name ) references Parent table ( Parent table field name );

                  Deletion of constraints ：

                                 Delete not null constraint ：alter table Table name modify Name type ;

                                 Delete unique constraint ：alter table Table name drop index Unique constraint name ;

                                 Delete primary key constraint ：alter table Table name drop primary key;

                                 Delete foreign key constraint ：alter table Table name drop foreign key Foreign key name ;

Two 、DML（ Data operation language ）

        explain ： Used to manipulate data contained in database objects

        command ：insert、update、delete

    Basic grammar ：

                Data increase ：insert into Table name ( Field name , Field name ... Field name ) values( value , value ... value );

                Data deletion ： keyword delete, The main function is to delete the existing records in the database table , It can be modified according to the conditions .

                               delete from Table name where Clause

                where ： Conditional statements

                Data modification ： Keywords are update, The main function is to modify the existing records in the database table , It can be modified according to the conditions

                                update Table name set Field name = value , Field name = value ... where Clause

                  Clear the table ：truncate Table name

3、 ... and 、DQL（ Data query language ）

        explain ： Used to query database data

        command ：select

    Basic grammar ：

                Inquire about ：select * from Table name ;

                The field is aliased ：select Field name as ' Field alias ', Field name as ' Field alias ' from Table name ;

                duplicate removal ：select distinct Field name 1, Field name 2, Field name 3... from Table name ;

                Conditional query （where Clause ）：select * from Table name where Conditions ;

                Fuzzy query （like）：select* from Table name where Field like Conditions ;

                Find in a specific range ：select * from Table name where Field in（ value 1, value 2...）;

                null Value query ：select * from Table name where Field is null;

                Aggregate functions ：count( Field ) -- Number of Statistics

                                  avg( Field ) -- Average

                                  sum( Field ) -- The sum of the

                                  max( Field ) -- Maximum

                                  min( Field ) -- minimum value

                grouping ：group by Field

                Sort （order by ）：select * from Table name  order by Field name 【desc/asc】

                Pagination （limit）：select * from Table name limit

That's all MySql The most basic grammar , Remember and use flexibly .