Conditional Execution

You can control the flow of execution in your stored program by using IF or CASE statements. Both have roughly the same functionality; we will demonstrate the use of IF in this tutorial, as it's probably the most familiar of the two constructs.

Figure 2-8 shows a stored program that works out the discounted rate for a purchase based on the size of the purchase, and Example 2-5 shows its execution. Purchases over $500 get a 20% discount, while purchases over $100 get a 10% discount.

Figure 2-8. Conditional execution with the IF statement


Example 2-5. Creating and executing a stored procedure that contains an IF statement

mysql> SOURCEdiscounted_price.sql
Query OK, 0 rows affected (0.01 sec)

Query OK, 0 rows affected (0.00 sec)

mysql> CALLdiscounted_price(300,@new_price) $$
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT@new_price$$
| @new_price |
| 270.0 |
1 row in set (0.00 sec)

The IF statement allows you to test the truth of an expression such as normal_price > 500 and take appropriate action based on the result of the expression. As with other programming languages, the ELSEIF clause is used for all conditional branches after the initial IF. The ELSE clause is executed if the Boolean expressions in the IF and ELSEIF clauses all evaluate to false.

CASE has very similar functionality, and may be preferable when you are comparing a single expression against a set of possible distinct values. The two conditional statements are explored and contrasted in Chapter 4.

Part I: Stored Programming Fundamentals

Introduction to MySQL Stored Programs

MySQL Stored Programming Tutorial

Language Fundamentals

Blocks, Conditional Statements, and Iterative Programming

Using SQL in Stored Programming

Error Handling

Part II: Stored Program Construction

Creating and Maintaining Stored Programs

Transaction Management

MySQL Built-in Functions

Stored Functions


Part III: Using MySQL Stored Programs in Applications

Using MySQL Stored Programs in Applications

Using MySQL Stored Programs with PHP

Using MySQL Stored Programs with Java

Using MySQL Stored Programs with Perl

Using MySQL Stored Programs with Python

Using MySQL Stored Programs with .NET

Part IV: Optimizing Stored Programs

Stored Program Security

Tuning Stored Programs and Their SQL

Basic SQL Tuning

Advanced SQL Tuning

Optimizing Stored Program Code

Best Practices in MySQL Stored Program Development

MySQL Stored Procedure Programming
MySQL Stored Procedure Programming
ISBN: 0596100892
EAN: 2147483647
Year: 2004
Pages: 208

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