tailieunhanh - Teach Yourself PL/SQL in 21 Days- P3

Teach Yourself PL/SQL in 21 Days- P3: Welcome to Sams Teach Yourself PL/SQL in 21 Days, Second Edition. The fact that you purchased this book indicates that you have an interest in learning the PL/SQL language, which is Oracle’s relational database procedural programming language. It allows you to develop powerful and complex programs to access and manipulate data in the Oracle8i database. We have attempted to include as many examples of PL/SQL code as possible to illustrate PL/SQL features | Writing PL SQL Expressions 77 Syntax J Syntax AND The AND operator is used to join two comparison expressions when you are interested in testing whether both expressions are true. It can also be used for the same purpose with two Boolean variables to check to see whether both are equal to true. The Syntax for the and Operator boolean_expression AND boolean_expression In this syntax boolean_expression can be any expression resulting in a Boolean or true false value. This is often a comparison expression such as a b but can also be a variable of the BOOLEAN datatype. The AND operator returns a value of true if both expressions each evaluate to true otherwise a value of false is returned. Use AND when you need to test several conditions and execute some code only when they are all true. Table shows some sample expressions using the AND operator. 3 Expressions Using the AND Operator Expression Result 5 5 AND 4 100 AND 2 2 true 5 4 AND 5 5 false Mon IN Sun . Sat AND 2 2 false OR The OR operator is used to join two comparison expressions when you are interested in testing whether at least one of them is true. It can also be used with two Boolean variables to see whether at least one is set to true. The Syntax for the OR Operator boolean_expression OR boolean_expression In this syntax boolean_expression can be any expression resulting in a Boolean or true false value. This is often a comparison expression such as a b but can also be a variable of the BOOLEAN datatype. The OR operator returns a value of true if any one of the expressions evaluates to true. A value of false is returned only if both the expressions evaluate to false. Table shows some sample expressions using the OR operator. 78 Day 3 Table Expressions Using the OR Operator Expression Result 5 o 5 OR 4 100 OR 2 2 false 5 4 OR 5 5 true Mon IN Sun . Sat OR 2 2 true Syntax String Operators PL SQL has two operators specifically designed to operate only on character string data. These are the LIKE