Expert help needed with tricky query

Question

I have a query database with a real simple schema but a tricky requirement: i need to display records with a simple select but then filter the result based on the authority/access level of the user making the query.
The source data is held in a table with just the following columns:
SRCTABLE:
subject_ID
date
data_ID
data_item
All column types are text strings and the first 3 are a composite key. There are 10s of millions of records in the table.
The access authorization is held in another table with the following columns:
ACCTABLE:
data_ID
access1
access2
accessn
The ellipsis means there are as many (boolean type) access1...n columns as there are distinct access levels to the source data.
The table contains one row for each distinct data_ID appearing in the source table. On each row the TRUE values in the access1...n columns indicate authorization to see the data item and the filter should leave that row in the result set.
The question then is how to write the query statement? It is assumed that the access id (i.e. the relevant column) is known when the query is made.
Something like
SELECT data_item FROM SRCTABLE
WHERE subject_ID="xxx" AND date = "1/1/2000";
would do it except for the need to filter each row based on the access authorization of the user.
Any help would be appreciated.

Answer 1

Thanks everybody for responding.
APC has a good point about really protecting every single item type separately. Unfortunately this is precisely the case. The security in this case is not oriented to increasing security in a levels oriented way. Rather each kind of item is protected by a need to know type security related to that particular item. Users are classified by their need to know a combination of the item types and those combinations are not in any sense consistent (and there will be new classes over time). This way access control necessarily becomes a matrix of item types vs access classes.
Fortunately this particular database does not exist yet so i am free to solve the problem in any way that fulfills the requirement. This is just the suggested form. I am not entirely happy with it hence the question on this forum in the first place.
So, i appreciate it should you have any further suggestions for optimal solution to handle the requirements. Again, those are:
1. A query that returns the data_items for a given ID and date (this is dead simple)
2. A filter (preferably in the query) that filters out those data_items the current user (his/her access class is known) is not authorized to see.
3. The plan calls for a table listing every possible item type with a column for each access class, enumerating the items allowed for that class. Any other solution to this issue would be acceptable provided it is capable to independently validate any single item type against any access class.
I hope this makes sense.