Merging Rows Within Same Table

I need to populate a table from several sources of raw data. For a
given security (stock) it is possible to only receive PARTS of
information from each of the different sources. It is also possible
to have conflicting data.

I am looking to make a composite picture of a given security using the
following rules:

1) The goal is to replace all NULL and Blank values with data

2) Order of precedence (from highest to lowest) is Non-NULL Non-Blank
--> Blank --> NULL

3) In the case of Non-NULL Non-Blank values that conflict (are
different) leave existing value (even if NULL or Blank)

For example:

Given the following rows:

Symbol Identity IdSource Exchange Type SubType Name
-------- ------------ --------- --------- ------- ---------
------------------
TZA 901145102 CUSIP XNYS Stock NULL TV AZTECA
TZA 901145102 NULL NULL NULL NULL

WSM 969904101 CUSIP XNYS Stock NULL WILLIAMS
SONOMA
WSM 969904101 NULL XNYS Stock NULL
WILLIAMS-SONOMA
WSM CUSIP XNYS Stock Common NULL
WSM NULL CUSIP XASE Stock NULL WILLIAMS
SONOMA

TYC 902124106 CUSIP XNYS Stock NULL TYCO
TYC 902124106 CUSIP XNYS Stock NULL TYCO
INTERNATIONAL


I am looking for the following results ('*' indicates changed value)

Symbol Identity IdSource Exchange Type SubType Name
-------- ------------ --------- --------- ------- ---------
------------------
TZA 901145102 CUSIP XNYS Stock NULL TV AZTECA
TZA 901145102 *CUSIP *XNYS *Stock NULL *TV AZTECA

WSM 969904101 CUSIP XNYS Stock *Common WILLIAMS
SONOMA
WSM 969904101 *CUSIP XNYS Stock *Common
WILLIAMS-SONOMA
WSM *969904101 CUSIP NULL Stock Common NULL
WSM *969904101 CUSIP XASE Stock *Common WILLIAMS
SONOMA

TYC 902124106 CUSIP XNYS Stock NULL TYCO
TYC 902124106 CUSIP XNYS Stock NULL TYCO
INTERNATIONAL