Exam FC0-U61 topic 1 question 93 discussion

Data Definition Language (DDL) commands refer to SQL commands that add to or modify the structure of the database. Some examples of data definition commands are: CREATE—this command can be used to add a new database on the RDBMS server (CREATE DATABASE) or to add a new table within an existing database (CREATE TABLE). The primary key and foreign key can be specified as part of the table definition. ALTER TABLE—this allows you to add, remove (drop), and modify table columns (fields), change a primary key and/or foreign key, and configure other constraints. There is also an ALTER DATABASE command, used for modifying properties of the whole database, such as its character set. DROP—this is the command used to delete a table (DROP TABLE) or database (DROP DATABASE). Obviously, this also deletes any records and data stored in the object. CREATE INDEX—specifying that a column (or combination of columns) is indexed speeds up queries on that column. The tradeoff is that updates are slowed down slightly (if the column is not suitable for indexing, updates may be slowed down quite a lot.) The DROP INDEX command can be used to remove an index.