This document defines SQL data definition statements and basic SQL query structure. It discusses DDL statements like CREATE, ALTER, and DROP that are used to define and manage database structures. It also explains the typical components of an SQL query including the SELECT, FROM, and WHERE clauses. Finally, it outlines several set operations in SQL like UNION, UNION ALL, INTERSECT, and MINUS.

1. BY
Ms V.VENNILA MCA., M.Phil..,
Assistant Professor
Bon Secours College for Women, Thanjavur.

2. Data Definition:
 Data definition refers to the set of SQL commands that
can create and manipulate the structures of a database.
 DDL statements are used to create, change and remove
objects including indexes, triggers, tables and views.
 Common DDL statements include
 CREATE
(generates a new table)
 ALTER
(alters table)
 DROP
(removes a table from the database)

3. CREATE:
Syntax:
CREATE TABLE table name(column definitions,table
parameters);
Example:
CREATE TABLE Employee(employee ID integer primary
key, first name char(50),last name(75))
ALTER:
Syntax:
ALTER object type, object name parameters
Example:
ALTER TABLE Employee ADD DOB date

4. Drop:
Syntax:
DROP object type object name
Example:
DROP TABLE Employee
BASIC STRUCTURE OF SQL QUERIES
 SQL is based on set relational operations with
certain modification and enhancements.
 A typical SQL query has the form
 The Select clause
 The From clause
 The Where clause

5. The SELECT clause:
 The select clause list the attributes described in the
result of a query.
 SQL allows duplicates in relations as well as in query
results.
 The select clause can contain arithmetic expressions
involving the operation +,-,* and / operating on
constants o attributes of tuples.
The WHERE clause:
 The where clause specifies conditions that the result
must satisfy.
 Comparison results can be combined using the logical
connectives and, or, not.
 Comparison can be applied to results of arithmetic
expressions.

6. The FROM clause:
 The from clause is a source of a row set to be operated
upon in a data manipulation language(DML) statement.
The from is an SQL reserved word in the SQL standard.
 The from clause is used in conjunction with SQL
statements.
SET OPERATIONS IN SQL
 SQL supports few set operations which can be performed
on the table data.
 These are used to get meaningful results from data
stored in the table under different special conditions.

7. Types of set operations:
 Union
 Union all
 Intersect
 Minus
Union Operation:
Union is used to combine the results of two or more
select statements.
Union All:
This operation is similar to union but it also shows the
duplicate rows.
Intersect:
Intersect operation is used to combine two select
statements.

8. Minus:
The minus operation combines results of two select
statements and return only those in the final result which
belongs to the first set of the result.