Key Features of a User-Defined Variable

• A User-Defined Variable is session specific i.e variable defined by one client is not shared to other client and when the session ends these variables are automatically expired.
• These variables are not case-sensitive. So, @mark or @Mark both refer to same value.
• Maximum length of variables can be 64 characters.
• Variable name can include other characters like- {!, #, ^, -, ..} in its name, if they are quoted. For ex- @’var@1′ or @”var^2″ or @`var3`.
• These variables can’t be declared, they are only initialized i.e at time of declaration they should be assigned a value.
• An undeclared variable can also be accessed in a SQL statement but their values is set as NULL.
• These variables can take values from the following set of datatypes- { integer, floating-point, decimal, binary, nonbinary string or NULL value}.

User-Defined Variables in are a way to store temporary values that can be used within a session. These variables are unique to a session and are not persistent across multiple sessions. They can be very useful for storing intermediate results or values that you want to reuse within a single session.

MySQL also supports the concept of User-defined variables, which allows passing of a value from one statement to another. A user-defined variable in MySQL is written as @var_name where, var_name is the name of the variable and can consist of alphanumeric characters, ., _, and $.