DDL:
Create database : create database database name;
display all databases : show databases;
delete database : drop database database name;
Use database : use database name;
Create table : create table table name (
field 1 name data type (length) [not null] [primary key] [auto_increment],
field 2 name data type (length) [default 'default value']
)
use table:
change Field type and length: alter table table name modify the type (length) of the field to be changed;
change field name and type and length: alter table table name change old field name new field name type (length);
add field: alter table table name add new field name type (length);
Write three sentences together:
alter table table name modify the type (length) of the field to be changed, change old field name, new field name type (length), add new field name type (length);
Modify the table name:
Rename table old table name to new table name;
Set the foreign key:
Alter table To set the table name of the foreign key add constraint foreign key name foreign key (associated field name) references associated table name (associated field name)
Delete foreign key:
Alter table to delete the foreign key table name drop foreign key foreign key name;
Delete field :
Alter table table name drop column field name;
Delete table:
Drop table table name;
DML:
Insert data :
1) All fields are inserted: insert into table name values (field value 1, field value 2 ...);
2) Select the corresponding insert: insert into table name (field 1, field 2) values (field value 1, Field value 2 ...);
3) Insert multiple rows of data: insert into table name values (field value 1, field value 2 ...), (field value 1, field value 2 ...) ...;
Note for INSERT statement :
When inserting data into string, char, varchar, text, and date fields, the field value should be enclosed in single quotes.
When inserting data into the auto-increment field, it is recommended to insert a NULL value. At this time, the next number will be inserted into the auto-increment field.
When inserting data into a default value constraint field, the field keyword can use the default keyword, indicating that the default value of the field is inserted.
When inserting a new record, you need to pay attention to the foreign key constraint relationship between the tables. In principle, you first insert data for the master (parent) table, and then insert data for the slave (child) table.
Modify the data :
Update table name set Field name to be modified 1 = new value, field name to be modified 2 = new value ... where primary key field name = primary key value corresponding to the value to be modified
Delete data :
delete one: delete from table name where primary key field name = primary key value corresponding to the value to be deleted
Delete all : delete from table name
Copy table :
Create table new table name like old table name;
Copy table data :
Insert into new table name select * from old table name;
To delete the associated foreign key data: when
creating a foreign key, set to: set null / cascade
