Partial updates to text and image data

Open Client supports the partial update of text and image columns. A partial update allows you to specify the part of the text or image field that you want to replace, delete, or insert, and to update that part only instead of modifying the entire field.

To perform a partial update, use ct_data_info to set iotype, delete_length, and offset. The values of delete_length and of the data passed to the server through ct_send_data determine the behavior of the partial update:

The ct_send_data routine can be used to send partially updated data. For partially updated data, the ct_send_data constructs a Transact-SQL updatetext statement, and the data is sent in chunks using multiple ct_send_data calls. The updatetext syntax is:

updatetext table_name.column_name text_pointer 
   {NULL | offset} {NULL | delete_length} [with_log]

If your client application performs partial updates on 2-byte Unicode datatypes, the application must make sure that it sends an even number of bytes to avoid a character split. You can use the buflen parameter of ct_send_data and the total_txtlen field of CS_IODESC to specify the length, in bytes, of the Unicode data. For Unitext, the offset and delete_length values must be specified as a character count while total_txtlen must be specified in bytes. For other datatypes, the offset, delete_length, and total_txtlen must be in bytes.