What does DDL mean?

What does DDL mean?

# DDL--DATA DEFINITION LANGUAGE
# ---------- Database -----------------
# Create a database
Create database day19;
# Create a database encoded as utf8
Create database day191 CHARSET UTF8;

# Show All Database names
Show databases;

# Viewing database creation Information
Show create database day191;
Show create database day19;
Show create database ex01;

# Deleting a specified database
Drop database day191;

# View the database in use
Select database ();

# Select a database
USE day19;
# View the database in use
Select database ();

# Show all tables in the database
Show tables;

# ---------- Table --------------
# Create a table and add fields
Create table abc (
Aid int primary key,
Aname VARCHAR (20) not null unique,
Aage int null );

Create table abcd (
Did int primary key,
Dname VARCHAR (20 ),
Ddate DATE
);

# Display table structure
DESC abc;
DESC abcd;

# Deleting a table abcd
Drop table abcd;
# Show All Tables
Show tables;

# Modify a table-Add a column
Alter table abc
ADD holobby VARCHAR (24) null default '0 ';
# Display table structure
DESC abc;

# Modify a table-delete a column
Alter table abc
DROP holobby;
# Display table structure
DESC abc;

# Modifying the data types and constraints of a column
Alter table abc
MODIFY aage VARCHAR (20 );
DESC abc;

# Modifying Field Names
Alter table abc
CHANGE aage age DOUBLE (3, 2) not null default 0;
DESC abc;

# Modifying table names
Rename table abc TO bbc;
DESC bbc;

Rename table bbc to abc;
DESC abc;