The host variable syntax is a symbol followed by a string, for example, :COMPANYNAME . The symbol that is used depends on the syntax that your database vendor uses to denote variables.
You can use a host variable in an SQL statement in place of an expression. You can use the Expression Builder wizard to create a host variable, or you can type a host variable in place of an expression in the SQL builder panes.
When you run the statement in the SQL builder, you are prompted to substitute a value of the appropriate type for the host variable.
After you run the statement, you can see what parameters were passed on the Parameters page in the Data Output view.