Oracle while exists(select ...) insert into - sql

Question

I am trying to insert id's into a temporary table with while loop.
TEMP_TABLE contains ID-s which = ID of entry in ID_TABLE.
ID_TABLE has two fields CON_1 and CON_2, which refer to another entry in ID_TABLE.
I want to add all CON_1 and CON_2 values from ID_TABLE into TEMP_TABLE where ID_TABLE.ID = TEMP_TABLE.ID and CON_1 or CON_2 are not already in TEMP_TABLE and then repeat the process until there are no IDs left to insert (after adding CON_1 or CON_2 to TEMP_TABLE, those ID-s might refer to ID_TABLE.ID where CON_1 or CON_2 are not already present in TEMP_TABLE).
Basically, an ID might have connections as another ID and I want to add ID, it's connections and the connections for the connections ... into TEMP_TABLE.
The query I made this far:
begin
while exists(select extId
from (
select distinct case
when con.CON_1 = idTable.ID
then con.CON_2
else con.CON_1
end
as extId
from ID_TABLE idTable
inner join TEMP_TABLE temp on idTable.ID = temp.ID
inner join CONNECTIONS_TABLE con on con.CON_2 = idTable.ID
or con.CON_1 = idTable.ID)
where not exists(select ID from TEMP_TABLE where ID = extId))
loop
insert into TEMP_TABLE
select extId
from (
select distinct case
when con.CON_1 = idTable.ID
then con.CON_2
else con.CON_1
end
as extId
from ID_TABLE idTable
inner join TEMP_TABLE temp on idTable.id = temp.ID
inner join CONNECTIONS_TABLE con on con.CON_2 = idTable.id
or con.CON_1 = idTable.ID)
where not exists(select ID from TEMP_TABLE where ID = extId);
end loop;
end;
When I run the query, I get this error:
PLS-00103: Encountered the symbol "INNER" when expecting one of the following:
) , with group having intersect minus order start union where
connect
Running on Oracle 12c

Answer 1

You appear to be trying to recursively add CON_1 or CON_2 values from the CONNECTIONS_TABLE that were connected to a prior ID value in both the TEMP_TABLE and the ID_TABLE.
You don't appear to need the WHILE loop (or even PL/SQL) and can use a single MERGE statement and a hierarchical query:
MERGE INTO temp_table DST
USING (
SELECT DISTINCT
extid
FROM (
select con_1, con_2
from connections_table c
START WITH EXISTS(
SELECT 1
FROM ID_TABLE i
inner join TEMP_TABLE t
on ( i.id = t.ID )
WHERE i.id IN ( c.con_1, c.con_2 )
)
CONNECT BY NOCYCLE
PRIOR con_1 IN ( con_1, con_2 )
OR PRIOR con_2 IN ( con_1, con_2 )
)
UNPIVOT (
extid FOR con IN ( con_1 AS 1, con_2 AS 2 )
)
) src
ON ( src.extID = dst.id )
WHEN NOT MATCHED THEN
INSERT ( id ) VALUES ( src.extid );
Which for the initial setup:
CREATE TABLE temp_table( id ) AS
SELECT 1 FROM DUAL;
CREATE TABLE connections_table( con_1, con_2 ) AS
SELECT 1, 2 FROM DUAL UNION ALL
SELECT 3, 2 FROM DUAL UNION ALL
SELECT 3, 4 FROM DUAL UNION ALL
SELECT 5, 10 FROM DUAL;
CREATE TABLE id_table ( id ) AS
SELECT LEVEL FROM DUAL CONNECT BY LEVEL <= 10;
Would insert 3 rows and then:
SELECT * FROM temp_table;
Outputs:
ID
1
2
4
3
db<>fiddle here