Question

I have a table with references to other tables. Stored is the table name and the entity id.

Like this:

         ref_table

   id  | table_name | refId
-------+------------+-------
    1  |   test     |   6
    2  |   test     |   9
    3  |   other    |   5

Now I try to formulate an SQL/FUNCTION that returns the correct entities from the correct tables. Something like:

SELECT * FROM resolveId(3)

I would expect to get the entity with the id “5” from the table “other”. Is this possible? I would guess I can do it with a stored procedure (CREATE FUNCTION). The function would have to inspect the “ref_table” and return the name of the table to use in the SQL statement … but how exactly?

Answer 1

If you want to use the resuling entities in select statements or joins, you should use CREATE FUNCTION with RETURNS TABLE ( .. )

There is a limitation in HSQLDB routines which disallows dynamically creating SQL. Therefore the body of the CREATE FUNCTION may include a CASE or IF ELSE block that switches to a pre-defined SELECT statement based on the input value (1, 2, 3, ..).

The details of CREATE FUNCTION are documented here:
http://hsqldb.org/doc/2.0/guide/sqlroutines-chapt.html#N12CC4
There is one example for an SQL function with RETURNS TABLE.