SQL parameters and SQL variables can be referenced anywhere in an SQL procedure statement where an expression or variable can be specified.
Host variables cannot be specified in SQL functions, SQL procedures, or SQL triggers. SQL parameters can be referenced anywhere in the routine and can be qualified with the routine name. SQL variables can be referenced anywhere in the compound statement in which they are declared, including any statement that is directly or indirectly nested within that compound statement. If the compound statement where the variable is declared has a label, references to the variable name can be qualified with that label
All SQL parameters and SQL variables are considered nullable except SQL variables that are explicitly declared as NOT NULL. The name of an SQL parameter or SQL variable in an SQL routine can be the same as the name of a column in a table or view referenced in the routine. The name of an SQL variable can also be the same as the name of another SQL variable declared in the same routine. This can occur when the two SQL variables are declared in different compound-statements. The compound-statement that contains the declaration of an SQL variable determines the scope of that variable. See compound-statement, for more information.
Names that are the same should be explicitly
qualified. Qualifying a name clearly indicates whether the name refers
to a column, global variable, SQL variable, or SQL parameter. If the
name is not qualified, or qualified but still ambiguous, the following
rules describe how the name is resolved. The name is resolved by checking
for a match in the following order:
If the name is still not resolved as a column,
SQL variable, or SQL parameter and the scope of the name included
a table or view that does not exist at the current server, it will
be assumed to be a column or global variable. If all the tables and
views exist at the current server, it will be assumed to be a global
variable.
The name of an SQL variable or SQL parameter in an SQL routine can be the same as the name of an identifier used in certain SQL statements. If the name is not qualified, the following rules describe whether the name refers to the identifier or to the SQL parameter or SQL variable:
In the CALL and ASSOCIATE LOCATORS statements, the
name is used as an identifier.