SQL Structure : The SQL language comprised of following parts:
Data Definition Language (DDL)
We know that RDBMS uses tables and the SQL-DDL provides commands for defining relation schema, deleting relations, creating indices, and modifying relation schema. DDL commands CREATE, ALTER and DROP used for creating, altering and removing relational schema. The SQL DDL includes commands for defining views which is a virtual table, in contrast to base tables whose tuples are actually stored in the database.
Data Manipulation Language (DML)
The SQL DML includes a query language based on both the relational algebra and tuple relational calculus. SQL uses SELECT command to retrieve information already existing in the database. It also includes commands to insert tuples into, delete tuples from and to modify tuples in the database.
Since SQL does not provide the full expressive capacity, as SQL cannot express all the QUERIES, the embedded form of SQL is designed for use within general-purpose programming language, such as PL/I, Cobol, Pascal, Fortran and C.
Authorization– The SQL DDL includes commands for specifying access rights to relations and views.
Integrity – the SQL DDL includes commands for specifying integrity constraints that the data stored in the database must satisfy. Updates that violate integrity constraints are disallowed.