store select result in variable and use in where condition - sql

Question

A have 3 SQL queries that I put together using union.
The first 2 queries return unique Order ID's but the third query repeats Order ID's from the first 2.I need to exclude those results in query 3 .
Example:
QUERY 1:
SELECT DISTINCT
ORDER_ID,
PRODUCT
FROM
ORDERS
WHEN TYPE=A
query 1 sample data {12121212,13131313}
QUERY 2:
SELECT DISTINCT
ORDER_ID,
PRODUCT,
FROM
ORDERS
WHEN CATEGORY=X
Query 2 sample data {14141414,15151515}
QUERY 3:
SELECT DISTINCT
ORDER_ID,
PRODUCT
FROM
ORDERS
WHEN TYPE=C
Query 3 sample data {17171717,12121212,14141414}
So query 3 repeats data from query 1 and 2. The real data is much larger. What I am trying to is to use the results of the first 2 queries to be excluded from query3
query1
union
query2
union
SELECT DISTINCT
ORDER_ID,
PRODUCT
FROM
ORDERS
WHEN TYPE=C
AND
ORDER_ID NOT IN (Variable1=ORDER_ID IN QUERY1,Variable2=ORDER_ID IN QUERY2)
Desired data {12121212,13131313,14141414,15151515,16161616,17171717}
How can I store variables to use in the where condition ?
Appreciate any help

Answer 1

It seems (but it is really hard to guess with any certainty) that you maybe want to do hierarchical data gathering, whether data is selected from 1st available source (from prioritized list), that has it, and next sources would get ignored.
Best of all I think would be making a persistent table having it all:
ORDER_ID, PRODUCT, Source_Priority
Such a table would track up-to-date data from all the tables (for example by AFTER UPADTE OR INSERT OR DELETE trigger on ORDERS and other sources) and then your query would be reformulated as "query new table, get rows with maximum-per-ORDER_ID-value-of-Source_Priority", which was asked many times, and is solved by one JOIN in Firebird 2 or by Window Functions in Firebird 3.
If you do not want to have a dedicated persistent prioritized table, You can do it, using
Global Temporary Table to do the sorting
https://firebirdsql.org/file/documentation/reference_manuals/fblangref25-en/html/fblangref25-ddl-tbl.html#fblangref25-ddl-tbl-gtt
MERGE command to do conditional inserts (clearing the table before it)
https://firebirdsql.org/file/documentation/reference_manuals/fblangref25-en/html/fblangref25-dml-merge.html
SELECT to read the data from prepared GTT
If you want to pretend that would be one query, not 2+N, then you can hide them inside
a named Stored Procedure or an anonymous EXECUTE BLOCK https://firebirdsql.org/file/documentation/reference_manuals/fblangref25-en/html/fblangref25-dml-execblock.html
Something like that:
Create GLOBAL TEMPORARY TABLE TMP_ORDERS
( ORDER_ID integer PRIMARY KEY,
PRODUCT VarChar(10) );
And then replace your "one true query" with this sequence (maybe hidden inside the Execution Block if need be)
DELETE FROM TMP_ORDERS;
INSERT INTO TMP_ORDERS
SELECT DISTINCT
ORDER_ID,
PRODUCT
FROM
ORDERS
WHEN TYPE=A;
MERGE INTO TMP_ORDERS as Dest
USING (
SELECT DISTINCT
ORDER_ID,
PRODUCT,
FROM
ORDERS
WHEN CATEGORY=X
) as Src
WHEN NOT MATCHED THEN
INSERT(Dest.ORDER_ID, Dest.PRODUCT) VALUES(Src.ORDER_ID, Src.PRODUCT);
MERGE INTO TMP_ORDERS as Dest
USING (
SELECT DISTINCT
ORDER_ID,
PRODUCT,
FROM
ORDERS
WHEN TYPE=C) as Src
WHEN NOT MATCHED THEN
INSERT(Dest.ORDER_ID, Dest.PRODUCT) VALUES(Src.ORDER_ID, Src.PRODUCT);
SELECT * FROM TMP_ORDERS;
P.S. but why did your partial queries even contained DISTINCT ? Isn't ORDER_ID already your primary key there, which can never be non-distinct, to start with?

Answer 2

you can try this
select * from
(SELECT DISTINCT
ORDER_ID,
PRODUCT
FROM
ORDERS
where TYPE='A') as q1,
(SELECT DISTINCT
ORDER_ID,
PRODUCT
FROM
ORDERS
WHERE CATEGORY='X'
) as q2,
(SELECT DISTINCT
ORDER_ID,
PRODUCT
FROM
ORDERS
where TYPE='C') as q3
WHERE q1.order_id=q2.order_id