MySQL Stored Procedure Programming

Chapter 4. Blocks, Conditional Statements, and Iterative Programming

This chapter describes the constructs in the MySQL language that control the scope and flow of execution.

In MySQL, as in all block-structured languages, groups of statements may be grouped together into blocks . A block can normally occur whenever a single statement would be permitted, and the block may contain its own distinct variable, cursor, and handler declarations.

The MySQL stored program language supports two types of stored program control statements: conditional control statements and iteration (looping) statements. Almost every piece of code you write requires conditional control, which is the ability to direct the flow of execution through your program based on a condition. You do this with IF-THEN-ELSE and CASE statements.

Iterative control structures—otherwise known as loops—let you execute the same code repeatedly. MySQL provides three different kinds of loop constructs:

Simple loop

Continues until you issue a LEAVE statement to terminate the loop

REPEAT UNTIL loop

Continues until an expression evaluates as true

WHILE loop

Continues as long as an expression evaluates as true

Block Structure of Stored Programs

Most MySQL stored programs consist of one or more blocks (the only exception is when a stored program contains only a single executable statement). Each block commences with a BEGIN statement and is terminated by an END statement. So in the simplest case, a stored program consists of a program ...