Attachment tables
There are two attachment tables: the attachment details table and the attachment
data table.

Attachment details table
The Attachment details table contains information for the properties of
Attachment fields. For every Attachment field in the form, a separate table is
created to store the attachment value.
The Attachment details table is named with a B followed by the unique ID for the
form (for example, B3).An attachment details table with one column (C1) is created with every
form.
For every attachment field added to any attachment pool on the form, three
columns are added. Each column is named with C, CO, or CC, followed by the
attachment field ID. For example, the three columns added for one attachment
might be called C536870920, CO536870920, and CC536870920, where 536870920
is the attachment field ID.
The C column stores the full path name of the attached file. The CO column stores
the original size (in bytes) of the attached file. The CC column stores the
compressed size (in bytes) of the attachment file.

Attachment data table
For each attachment field on a form, an attachment data table is created. The
attachment data table is named with a B followed by the unique ID for the form,
followed by C, followed by the attachment field ID. For example, the attachment
data table might be called B7C536870920, where 7 is the schemaID, and
536870920 is the attachment field ID.
The Attachment data table has two columns: one that holds the Request ID
(entryId) and one that holds the data from the file. The column holding the data
is named with a C followed by the attachment field ID. For example, the data
column might be named C536870920, where 536870920 is the attachment field ID