Datasheet

Writing Simple Queries

are returned or operated upon where the data satisﬁes the logical condition(s) of the WHERE

clause. You can use column names or expressions in the

WHERE clause, but not column alias

names. The

WHERE clause follows the FROM clause in the SELECT statement.

How do you list the employees who work for department 90? The following example

shows how to limit the query to only the records belonging to department 90 by using a

WHERE clause:

SELECT first_name || ‘ ‘ || last_name “Name”, department_id

FROM employees

WHERE department_id = 90;

Name DEPARTMENT_ID

------------------------------------------- -------------

Steven King 90

Neena Kochhar 90

Lex De Haan 90

You need not include the column names in the SELECT clause to use them

in the

WHERE clause.

You can use various operators in Oracle 11g in the WHERE clause to limit the number of rows.

Comparison Operators

Comparison operators compare two values or expressions and give a Boolean result

TRUE, FALSE, or NULL. The comparison operators include those that test for equality,

inequality, less than, greater than, and value comparisons.

= (Equality)

The = operator tests for equality. The test evaluates to TRUE if the values or results of an

expression on both sides of the operator are equal.