How to overcome SQLite View limitation - sql

Question

Given that in SQLite, Views:
are read-only
cannot be UPDATEd,
the following is the situation:
There are 4 tables A, B, C and D and a View has to be created with data from all the four tables conditionally. Here's the pseudo-construct:
CREATE VIEW AS E SELECT A.A1, A.A2, A.A3, A.A4, B.B1, C.C1, C.C2, D.D1, D.D2 FROM A, B, C, D
WHERE A.X = 'SOME STRING' AND
A.FK = C.PK AND
A.Y = B.Z AND
D.G = A.PK AND
D.H = 'SOME STRING'
The requirement is that, irrespective of no matches in D, the remaining matches should get populated, (with 0 values in the view E for the columns from D). Needless to say, the above construct works if there are matching D rows, but obviously returns an empty view if there are no D matches.
How can the CASE statement or SELECT sub-queries (or an altogether different construct, like an INSTEAD OF trigger) deliver this requirement?
Greatly appreciate if the database experts could publish the exact construct(s). Many, many thanks in advance!

Answer 1

First, use explicit joins:
SELECT A.A1, A.A2, A.A3, A.A4, B.B1, C.C1, C.C2, D.D1, D.D2
FROM A
JOIN B ON A.Y = B.Z
JOIN C ON A.FK = C.PK
JOIN D ON D.G = A.PK
WHERE A.X = 'SOME STRING'
AND D.H = 'SOME STRING';
Then you can use an outer join when you want to keep rows without a match:
FROM A
JOIN B ON A.Y = B.Z
JOIN C ON A.FK = C.PK
LEFT JOIN D ON D.G = A.PK AND D.H = 'SOME STRING'
WHERE A.X = 'SOME STRING';
(The D.H comparison must be part of the join condition because D.H is NULL for missing rows, and the comparison would fail in the WHERE clause.)