Concat columns from multiple tables into one row without duplicates - sql

Question

I need to concatenate two columns from diffrent tables, delimited with ";" into one row without duplicates.
Table 1:
Name
John;Sue
Table 2:
Name
Mary;John
Desired output
Names
John;Sue;Mary
I tried with :
select listagg(a.Name, ';') within group (order by a.Name) as Names
from Table1 a
join Table2 b on a.id = b.id;
but I get "ORA-01489: result of string concatenation is too long" error.
How to do that properly in Oracle?

Answer 1

You can do it with simple string functions:
WITH t1_positions (id, name, spos, epos) AS (
SELECT id,
name,
1,
INSTR(name, ';', 1)
FROM table1
UNION ALL
SELECT id,
name,
epos + 1,
INSTR(name, ';', epos + 1)
FROM t1_positions
WHERE epos > 0
),
t1_strings (id, item) AS (
SELECT id,
CASE epos
WHEN 0
THEN SUBSTR(name, spos)
ELSE SUBSTR(name, spos, epos - spos)
END
FROM t1_positions
),
t2_positions (id, name, spos, epos) AS (
SELECT id,
name,
1,
INSTR(name, ';', 1)
FROM table2
UNION ALL
SELECT id,
name,
epos + 1,
INSTR(name, ';', epos + 1)
FROM t2_positions
WHERE epos > 0
),
t2_strings (id, item) AS (
SELECT id,
CASE epos
WHEN 0
THEN SUBSTR(name, spos)
ELSE SUBSTR(name, spos, epos - spos)
END
FROM t2_positions
)
SELECT id,
LISTAGG(item, ';') WITHIN GROUP (ORDER BY item) AS name
FROM (SELECT * FROM t1_strings
UNION
SELECT * FROM t2_strings)
GROUP BY id;
Which, for the sample data:
CREATE TABLE Table1 (id, name) AS
SELECT 1, 'John;Sue' FROM DUAL;
CREATE TABLE Table2 (id, name) AS
SELECT 1, 'Mary;John' FROM DUAL;
Outputs:
ID
NAME
1
John;Mary;Sue
Note: you can do it with regular expressions; however, for a large dataset, it is likely to be of an order of magnitude slower.
Update
How to do that properly in Oracle?
Do not store delimited strings and store the data in first normal form (1NF):
CREATE TABLE table1 (id, name) AS
SELECT 1, 'John' FROM DUAL UNION ALL
SELECT 1, 'Sue' FROM DUAL;
CREATE TABLE table2 (id, name) AS
SELECT 1, 'Mary' FROM DUAL UNION ALL
SELECT 1, 'John' FROM DUAL;
Then the query is simply:
SELECT id,
LISTAGG(name, ';') WITHIN GROUP (ORDER BY name) AS name
FROM (SELECT * FROM table1
UNION
SELECT * FROM table2)
GROUP BY id;
db<>fiddle here

Answer 2

Presuming those are names and the result doesn't span over more than 4000 characters (which is the listagg limit) then one option is to do this (read comments within code):
SQL> with
2 -- sample data
3 table1 (id, name) as
4 (select 1, 'John;Sue' from dual union all
5 select 2, 'Little;Foot' from dual),
6 table2 (id, name) as
7 (select 1, 'Mary;John' from dual),
8 --
9 union_jack (id, name) as
10 -- union those two tables
11 (select id, name from table1
12 union
13 select id, name from table2
14 ),
15 distname as
16 -- distinct names
17 (select distinct
18 id,
19 regexp_substr(name, '[^;]+', 1, column_value) name
20 from union_jack cross join
21 table(cast(multiset(select level from dual
22 connect by level <= regexp_count(name, ';') + 1
23 ) as sys.odcinumberlist))
24 )
25 select id,
26 listagg(d.name, ';') within group (order by d.name) as names
27 from distname d
28 group by id;
ID NAMES
---------- ------------------------------
1 John;Mary;Sue
2 Foot;Little
SQL>
If it really spans over more than 4000 characters, switch to XMLAGG; lines #25 onward would be
25 select id,
26 rtrim(xmlagg (xmlelement (e, d.name || ';') order by d.name).extract
27 ('//text()'), ';') as names
28 from distname d
29 group by id;
ID NAMES
---------- ------------------------------
1 John;Mary;Sue
2 Foot;Little
SQL>

Answer 3

You can use a XML-style tecnique before applying LISTAGG() in order to provide writing distinct names such as
WITH t AS
(
SELECT RTRIM(DBMS_XMLGEN.CONVERT(
XMLAGG(
XMLELEMENT(e,name||';')
).EXTRACT('//text()').GETCLOBVAL() ,1),
';') AS name
FROM ( SELECT t1.name||';'||t2.name AS name
FROM table1 t1 JOIN table2 t2 ON t1.id=t2.id )
)
SELECT LISTAGG(REGEXP_SUBSTR(name,'[^;]+',1,level),';')
WITHIN GROUP (ORDER BY 0) AS "Names"
FROM t
CONNECT BY level <= REGEXP_COUNT(name,';')
Demo