Storage Definition Languages (SDL)

DBMS supports many languages out of which (SDL) is one of them. SDL stands for Storage Definition Language. SDL matter is almost anything that’s not specified by SQL standard. It is different in every DBMS which specifies anything to do with how or where data in relevant table is stored. It’s applications are as follows :

• Used to define internal schema.
• It defines physical structure of database.
• The order of fields.
• Bytes per field will be used.
• How records will be accesses etc.
• The mapping between two schema may also be defined.

Example : Let us take some examples to understand how Storage Definition Language (SDL) works. 

Example-1 :

CREATE TABLE geeksforgeeks (no_of_articles INT) ENGINE = INNODB;

In the above example, we specify storage engine to be used by adding ENGINE option. InnoDB is default storage engine for MySQL 8.0.

Example-2 :

CREATE TABLE geeksforgeeks (article_title varchar(65000) ENGINE = MEMORY;

This time, engine used is MEMORY. MEMORY storage engine (also known as HEAP) creates tables for particular purpose with contents that are stored in memory.
 Because the data is vulnerable to power outages, crashes or hardware issues, only use these tables as temporary work areas or read-only caches for data pulled from other tables. 

Example-3 :

CREATE TABLE f (x int, y varchar(25));

In the above statement, Storage Definition Language (SDL) defines storage of row int, varchar(25). 

Indeed, In most relational database management systems (RDBMS) there is no specific language that performs the role of SDL. Instead, combination of functions, parameters, and specifications related to storage of files define internal schema.