I'm looking for warehouse employment statistics by market/industry
segment, most importantly for retail and wholesale businesses.  How
many warehouse workers, for example, are employed in the warehouses of
supermarkets, discount stores, home centers, ...?  Even better would
be a breakdown by job category within the warehouse.  The BLS
Industry-Occupation employment matrix can generate something vaguely
like what I'm looking for, but it's extremely hard to interpret.

The Bureau of Labor Statistics has lots of data, though it?s not as
detailed as we might like. There is no category ?warehouse worker,?
but since you?re interested in retail and wholesale trade in
particular, the BLS category ?stock clerks and order fillers? is
probably the closest to your requirements. These workers are
considered ?Office and Administrative Support? positions. Under 
?Material Moving? positions, you might be interested in ?laborers and
freight, stock, and material movers,? and ?packers and packagers.?
The BLS? Occupational Outlook Handbook (http://bls.gov/oco/home.htm)
and Career Guide to Industries (http://bls.gov/oco/cg/home.htm) are
the best sources for this information.

For each of the above job descriptions, I?ll quote from the Handbook.

Stock clerks:

 ?Stock clerks and order fillers held about 1.6 million jobs in 2002;
they were, by far, the largest material-recording, -scheduling,
-dispatching, and -distributing occupation. About 75 percent work in
wholesale and retail trade. The greatest numbers are found in grocery
stores, followed by department stores. Jobs for stock clerks are found
in all parts of the country, but most work in large urban areas that
have many large suburban shopping centers, warehouses, and factories.?

http://bls.gov/oco/ocos139.htm - This link contains a wealth of
information about labor conditions, employment trends, and wages for
these workers.

Laborers and freight movers:

?Laborers and hand freight, stock, and material movers manually move
materials or perform other unskilled general labor. These workers move
freight, stock, and other materials to and from storage and production
areas, loading docks, delivery vehicles, ships, and containers. Their
specific duties vary by industry and work setting. Specialized workers
within this group include baggage and cargo handlers, who work in
transportation industries, and truck loaders and unloaders. In
factories, they may move raw materials or finished goods between
loading docks, storage areas, and work areas as well as sort materials
and supplies and prepare them according to their work orders.?
In 2002, 2,231,000 people worked in this occupation, only a small
number in merchant trades. I?ll provide employment data for this group
by different trade categories below.

Packers:

?Hand packers and packagers manually pack, package, or wrap a variety
of materials. They may inspect items for defects, label cartons, stamp
information on products, keep records of items packed, and stack
packages on loading docks. This group also includes order fillers, who
pack materials for shipment, as well as grocery store courtesy clerks.
In grocery stores, they may bag groceries, carry packages to
customers? cars, and return shopping carts to designated areas.?
In 2002, 2,231,000 people worked in this occupation, only a small
number in merchant trades. As you can see, most of these employees do
not work in stockrooms, but I?ll provide employment data for this
group regardless.

The above information about laborers and packers can be found at:
http://bls.gov/oco/ocos243.htm. This link also contains plenty of
additional information about material-moving jobs.

Regarding industry breakdowns, the BLS has four trade categories
(http://bls.gov/oco/cg/cg1003.htm):

Clothing, accessory, and general merchandise stores.
Grocery stores.
Auto dealers.
Wholesale trade.

I?ll provide 2002 employment data from the Career Guide to Industries
for the three job descriptions discussed earlier, broken down for each
of the four trade groups. If you?re interested in other job
descriptions, like shipping or order clerks, etc., check out the pages
I reference. They?re packed with data, including employment breakdowns
for a variety of jobs.


Clothing, accessory, and general merchandise stores

Stock clerks: 392,000
Laborers, freight movers, etc.: 118,000
Packers: 25,000

http://bls.gov/oco/cg/cgs022.htm 


Grocery stores

Stock clerks: 411,000
Laborers, freight movers, etc.: 33,000
Packers: 239,000

http://bls.gov/oco/cg/cgs024.htm


Auto dealers

Stock clerks: Not relevant.
Laborers, freight movers, etc.: 11,000
Packers: Not relevant.

http://bls.gov/oco/cg/cgs025.htm


Wholesale Trade

Stock clerks: 197,000
Laborers, freight movers, etc.: 344,000
Packers: 83,000

http://bls.gov/oco/cg/cgs026.htm 


You might also be interested in employment data for the ?Truck
Transportation and Warehousing? group
(http://bls.gov/oco/cg/cgs021.htm), but from my reading of the BLS Web
site, this is mainly warehousing for trucking companies or
distribution centers, and does not directly bear on your situation.



Search strategy: None, just tooled around BLS Web site and called the
information desk for assistance.

Although this answer does help distill some of the information from
the BLS site, it doesn't go any farther than that.  The "Career Guide
to Industries" data presented below is available in a single place -
the Industry-Occupation employment matrix referred to in the question.