MySQL Tutorials - Herong's Tutorial Examples

∟System, User-Defined and Stored Procedure Variables

This chapter provides tutorial notes on 3 types of variables in MySQL: System Variables, User-Defined Variables and Stored Procedure Variables. System variables have two scopes: Global and Session.

System Variables Like @@version

Scopes of System Variables: Global and Session

User-Defined Variables Like @x

User-Defined vs. Stored Procedure Variables

Takeaways:

• System Variables, @@Var, are variables used by MySQL Server to store parameters that represent system information or control system behaviors.
• You can use "SHOW [GLOBAL|SESSION|LOCAL] VARIABLES ..." to search and view global or session values of system variables.
• You can use "SET [GLOBAL|SESSION|LOCAL] Var = ..." to set global or session values of system variables.
• User-Defined Variables, @Var, are variables used in client sessions to carry information from one command to other later commands.
• Stored Procedure Variables, Var, are variables used locally in a given stored procedure.
• You can use "SET @@var|@Var|Var := expression" to assign values.
• You can use "SELECT expression INTO @@var|@Var|Var" to assign values.
• You can also use "SELECT (@@var|@Var|Var := expression)" to assign values once per each row.

Table of Contents

 About This Book

 Introduction of SQL

 MySQL Introduction and Installation

 Introduction of MySQL Programs

 PHP Programs and MySQL Server

 Perl Programs and MySQL Servers

 Java Programs and MySQL Servers

 Datatypes and Data Literals

 Operations and Expressions

 Character Strings and Bit Strings

 Commonly Used Functions

 Table Column Types for Different Types of Values

 Using DDL to Create Tables and Indexes

 Using DML to Insert, Update and Delete Records

 Using SELECT to Query Database

 Window Functions for Statistical Analysis

 Use Index for Better Performance

 Transaction Management and Isolation Levels

 Locks Used in MySQL

 Defining and Calling Stored Procedures

 Variables, Loops and Cursors Used in Stored Procedures

►System, User-Defined and Stored Procedure Variables

 MySQL Server Administration

 Storage Engines in MySQL Server

 InnoDB Storage Engine - Primary and Secondary Indexes

 Performance Tuning and Optimization

 Bulk Changes on Large Tables

 MySQL Server on macOS

 Installing MySQL Server on Linux

 Connection, Performance and Second Instance on Linux

 Archived Tutorials

 References

 Full Version in PDF/EPUB

System, User-Defined and Stored Procedure Variables - Updated in 2023, by Herong Yang