The columns being joined must have the same or compatible datatypes. Use the convert function when comparing columns whose datatypes cannot be implicitly converted. Columns being joined need not have the same name, although they often do.
If the datatypes used in the join are compatible, Adaptive Server automatically converts them. For example, Adaptive Server converts among any of the numeric type columns—int, smallint, tinyint, decimal, or float, and among any of the character type and date columns—char, varchar, unichar, univarchar, nchar, nvarchar, datetime, date and time. For details on datatype conversion, see Chapter 11, “Using the Built-In Functions in Queries,” and the “Datatype Conversion Functions” section of the Reference Manual.
