sub-select parameter problem

Hello,

Imagine the following query:

-------------------------------------------
SELECT
 tableA.field1, tableA.field2,  tableB.field1, tableB.field2,
 (   SELECT tableC.field2   FROM tableC   WHERE tableC.field1 = tableB.field1 - 1; ) AS p

FROM tableA
INNER JOIN tableB
ON tableA.pk = tableB.FK;
-------------------------------------------

It works fine.

Now, I need to do something else: the parameter of my sub-select is also
a member of the table I'm selecting.

-------------------------------------------
SELECT
 tableA.field1, tableA.field2,  tableB.field1, tableB.field2,
 (   SELECT tableB.field2   FROM tableB   WHERE tableB.field1 = tableB.field1 (--> from-main-select?) - 1; ) AS p

FROM tableA
INNER JOIN tableB
ON tableA.pk = tableB.FK;
-------------------------------------------

How can I refer to the tableB.field1 parameter from the main query? I've
tried to do something like this, but without success:

-------------------------------------------
SELECT
 tableA.field1, tableA.field2,  tableB.field1 AS param, tableB.field2,
 (   SELECT tableB.field2   FROM tableB   WHERE tableB.field1 = param - 1;    (--> does not work...) ) AS p

FROM tableA
INNER JOIN tableB
ON tableA.pk = tableB.FK;
-------------------------------------------

The only workaround I found is to use CASE... WHEN, but this is not
really robust, nor elegant.

-------------------------------------------
SELECT
 tableA.field1, tableA.field2,  tableB.field1, tableB.field2,
 CASE
 WHEN tableB.field1 = 1 THEN (   SELECT tableB.field2   FROM tableB   WHERE tableB.field1 = 0; )
 WHEN tableB.field1 = 2 THEN (   SELECT tableB.field2   FROM tableB   WHERE tableB.field1 = 1; )
 WHEN tableB.field1 = 3 THEN (   SELECT tableB.field2   FROM tableB   WHERE tableB.field1 = 2; )
 ... etc...
 ELSE 0
 END AS p,

FROM tableA
INNER JOIN tableB
ON tableA.pk = tableB.FK;
-------------------------------------------

In my particular application, this is almost acceptable, but I'm sure
there is a better way to do that...


Thanks for your help! (And for reading, by the way!)


-------------------------------
Philippe Lang
Attik System