-sql -DDL

Column operations

desc table; ...................................... # View table structure 
alter table table name add column name attribute; # add columns .............. 
alter table add column name of the attribute table after column name; ... # specify added behind a column 
alter table drop column table name; .............. # delete the column name 
alter table table name change old column names new column name for the new property ..... # modify the column name 
alter table a modify change_username varchar (20 ); # modify column properties

alter table a add new_username char (10 ); # add column 
alter table a add new_username2 char (10 ) after id; # add columns, designated added after a column 
alter table a drop new_username2; # delete column name 
alter table a change new_username change_username char (5); # modify the column name 
alter table a modify change_username varchar (20 ); # modify column properties

Operating Table

show tables; # View all the tables 
desc table name; # View table structure 
show create table table name; # Create a table view SQL 
show tables; # Display information 
show table status where name = 'table name'; # to view a table in a information 
rename table the old table to the new table name table name # modify 
delete from user_t; # Clear the table of contents 
truncate user_t; # id table of contents emptied from the beginning

# View 
show create view view name # View Jian view the process of 
drop view view name # delete the view 
create view v1 as select * from student2 # create the view behind as with ordinary SQL 
the Create View v2 as the SELECT the above mentioned id, name, Score from STUDENT2 # Create a view behind as with ordinary sql

index

. 1 
2 
. 3 
. 4 
. 5 
. 6 
. 7 
. 8 
. 9 
10 
. 11 
12 is 
13 is 
14 
15 
16 
. 17 
large column   -sql -DDL LASS = "Line"> 18 is 
. 19 
20 is 
21 is 
22 is 
23 is 
24 
25 
26 is 
27 
28 
29

# Ordinary index (index another name Normal), 
# unique index (UNIQUE), 
# full-text indexing (FULLTEXT), 
# space index (SPATIAL)

unique key email (email (10) ) # length using an index 
alter table table add index index name (field name) # add a normal index 
alter table table name drop index index name # delete index 
show index from the index table # View

create table a1(
    name char(5),
    email char(15),
    key name(name),
    unique key email(email)
);

# Multicolumn index 
Create Table A3 ( 
    name char (. 5), 
    In Email char (15), 
    Key name (name), 
    UNIQUE Key name_email (name, In Email) 
); 
EXPLAIN SELECT * from A3 the WHERE name = "Zhang"; # Analysis SQL 
the ALTER the Table a1 the Add uNIQUE (name); # add a unique index 
alter table a1 add index index_name (email ) # add a normal index 
alter table a1 drop index index_name # delete indexes 
show index from a1 G # View index

!!! library operations [This operation is more dangerous, please exercise caution]

create database database; # create database 
create database database default character set the character set collate collation; # specify the character set to create a library

create database yourdb; # create database 
create database yourdb3 default character set utf8mb4 collate utf8mb4_unicode_ci; # specify the character set to create a library

Name !!! databases do not directly modify, easy to lose data !!!

Not commonly used, have practical use sql

The SELECT 
    name, 
    NULL Hello the AS, --- NULL as a 
    "foo" AS bar --- string as a 
FROM student2

Add Column

Column operations

Operating Table

index

!!! library operations [This operation is more dangerous, please exercise caution]

Not commonly used, have practical use sql

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