A variable is declared by giving a name and data type. Data type determines the size and the range of values that can be stored within the variable and the set of operations that can be applied to the variable.
The name of a variable consists of letters, numerals, dollar signs, underscores, and number signs and should not exceed 30 characters. By default, variable names are not case-sensitive.
You cannot use a reserved keyword as a variable name.
A variable declaration specifies its name, data type, and value, and allocates storage for it. The declaration can also impose the NOT NULL constraint.