SQL Commands

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SQL commands (or statements) are generally grouped into two categories:

Data Manipulation Commands, which are used to obtain, add, remove and/or modify database information. More specifically, this refers to the SELECT, INSERT, UPDATE and DELETE commands.
Data Definition Commands, which are used to create or remove database objects or database structure objects. More specifically, this refers to the CREATE DATABASE, CREATE TABLE, ALTER TABLE, DROP INDEX, DROP TABLE or CREATE SCHEMA commands.

In the syntax, command names and keywords appear in bold and are passed "as is." Other elements appear in italics and are detailed separately in the chapter. Keywords and/or clauses that are passed in straight brackets [ ] are optional. The vertical bar character | separates the various alternatives available. When elements are passed in curly brackets { }, separated by vertical bars, this indicates that only one element of the set should be passed.