Query questions

I'm building a database containing key parameters for ~500,000 data
files. The design I found logical is

Two tables for each file:
1) Larger table with detailed key parameters
(10-15 columns, ~1000 rows), call it large_table
2) Small table with file summary
(~30 columns, 1 row), call it small_table

A major purpose is to gain the ability to identify all data in the original
archive (~3 terabyte) satisfying some criteria that can be specified in
the database queries. But I find the query options surprisingly limited
(or difficult - sure, things can be done if you write enough code...)
Here is what I would like to be possible:

SELECT <large_table columns> FROM <regular expression>
WHERE <condition on large_table>
IF <condition on corresponding small_table>;

In words: For each of many large_tables, check corresponding small
table and only process large_table if some condition is met.

2 problems:
1) Can't use regular expression to specify tables. Wouldn't that be nice?
Is it possible to specify a lot of tables without having to write custom
functions in e.g. plsql?
2) No IF statement. How do I issue commands (or redesign
database) so I can check the file summary before diving into the
large table? This ought to be simple...

Any input will be highly appreciated, thanks in advance!

Poul Jensen