The meaning of DDL
The SQL commands can be categorized into 4 main subsets:
- DDL – Data Definition Language. This includes these statements: CREATE, DROP, ALTER, TRUNCATE, RENAME, COMMENT
- DQl – Data Query Language. This includes all SELECT statements.
- DML – Data Manipulation Language. This includes INSERT, UPDATE, and DELETE statements.
- DCL – Data Control Language. This includes GRANT and REVOKE statements.
In this post, we are going to learn more about the DDL - Data Definition Language subsets.
DDL statements are used to make a change to the structure of the database schema, which involves creating, renaming, modifying, or deleting a database object such as database, table, and view.
It depends on which database management system you are using to have a corresponding subset of DDL statements as the functions and syntaxes might vary. But here is the list of common DDL statements in SQL:
CREATE: to create a new database or its objects such as table or view
DROP: to delete an existing database or its object
ALTER: to modify the structure of an existing database
TRUNCATE: to remove all existing records from the table and make it empty
COMMENT: to add comments to the data dictionary
RENAME: to rename a database or its object
- Create a new table:
CREATE TABLE table_name ( column1 datatype, column2 datatype, column3 datatype, .... );
- Drop an existing table:
DROP TABLE table_name;
- Alter an existing table to add a new column:
ALTER TABLE table_name ADD column_name datatype;
- Truncate a table:
TRUNCATE TABLE table_name;
- Rename table:
ALTER TABLE table_name RENAME TO new_table_name;
- Comment on a table:
COMMENT ON TABLE table_name IS 'Your comment';
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