Consider the Data Definition Language statements: “ALTER TABLE [My Table] ADD COLUMN [My New Field] Single” and “ALTER TABLE [My Table] ADD COLUMN [My New Field] Double”. According to Microsoft documentation, Double and Single are correct constants for field types dbDouble and dbSingle. Boolean is also indicated as the Type property for dbBoolean, yet “ALTER TABLE [My Table] ADD COLUMN [My New Field] Boolean” doesn’t work. Why?

Further reading about the Boolean datatype in the DAO documentation declares that Boolean is “A True/False or yes/no value. Boolean values are usually stored in Bit fields in a Microsoft Jet database; however, some databases don’t support this datatype directly.” “ALTER TABLE [My Table] ADD COLUMN [My New Field] Bit” works. Ironically, nothing is listed in the table of Type properties for dbBit or Bit itself.