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Using Qualifiers and Aliases

              When tables are joined, it's often the case that the tables contain columns with the same names. If such a column is referred to in the query, it's ambiguous which table the column reference applies to. This ambiguity usually can be addressed by qualifying column names with table names. However, if a join is on a table to itself, even the table name is ambiguous and it's necessary to use aliases to disambiguate table references. This section describes how to address naming issues in queries by qualifying column and table names and by using aliases. Qualifying Column Names                If a column name used in the query appears in more than one table, the name is ambiguous and it's necessary to provide information that identifies which table the column is connected to. This has been accommplished by qualifying the column name with the appropriate table name throughout the examples in this chapter. If name qualification has not been used, then pro