An introduction to the SQL statements

The SQL statements can be divided into two categories: the data manipulation language(DML) that let you work with the data in the database and the data definition language(DDL) that lets you work with the objects in the database.

SQL programmers typically work with the DML statements, while database adminstrators(DBAs) use the DDL statements.

 

The statements that work with the data in a database are called the data manipulation language(DML). 

SQL statements used to work with data(DML)

 

Statements	Description
SELECT	Retrieve data from one or more tables.
INSERT	Adds new rows to a table.
UPDATE	Changes existing rows in a table.
DELETE	Deletes existing rows from a table.

 

The statements that work with the objects in a database are called the data definition language(DDL). On large systems, these statements are used exclusively by database adminstrators, or DBAs. It's the DBA's job to maintain existing databases, tune them for faster performance, and create new databases. On smaller systems, though, the SQL programmer may fill the role of the DBA.

SQL statements used to work with database objects(DDL)

 

Statement	Description
CREATE USER	Creates a new user for a database.
CREATE TABLE	Creates a new table in a database.
CREATE SEQUENCE	Creates a new sequence that automatically generates numbers.
CREATE INDEX	Creates a new index for a table.
ALTER USER	Changes the definition of an existing user.
ALTER TABLE	Changes the definition of an existing table.
ALTER SEQUENCE	Changes the definition of an existing sequence.
ALTER INDEX	Changes the structure of an existing index.
DROP USER	Deletes an existing user.
DROP TABLE	Deletes an existing table.
DROP SEQUENCE	Deletes an existing sequence.
DROP INDEX	Deletes an existing index.
GRANT	Grants privileges to a user.
REVOKE	Revokes privileges from a user.