Assigning Values to a Blob Field

A blob field only accepts a char or alpha expression types assignments (or varchar or varalpha as well) because it is assumed that the expression being assigned contains the path of an operating system file to converted to a blob field.

An exception is when a null value is assigned to a blob field in which case it will not contain any blob information.

Getting Values from a Blob Field

By definition, a blob field contains either the length of the blob or a null value. Therefore, assigning a blob field to any other kind of field will result in a standard conversion of a numeric value to this field (it makes no sense assigning a blob field to a date field).

This also applies when listing the contents of a blob field where the result will always be a numeric value corresponding to the size of the blob.

Assigning a Blob Field to a Blob Field

This assignment, although admissible in nature, cannot be performed because it would copy the description of one blob to another, but not the blob itself. Since a given entity set or relationship with fields can only have one blob defined, the copy could only be performed between two different entity sets in which case the copied information would point to a blob that only exists in the original blob field, thus originating an error.