How to put the result of two different columns with same data type within one column such that both rows from both tables are unique in target table

Question

For example I have two columns:

Column A: dog, cat, mouse

Column B: truck, jeep, lorry

I want a situation where:

Column C : dog, truck, cat, jeep, mouse, lorry

I am using Snowflake

Answer 1

Assuming that columns colA, colB are strings, the values should be first splitted to atomic values SPLIT_TO_TABLE and combined again LISTAGG:

SELECT ID, COLA, COLB, LISTAGG(COL, ', ') AS colC
FROM (
  SELECT ID, COLA, COLB, TRIM(s1.VALUE::STRING) AS col
  FROM tab
  ,TABLE(SPLIT_TO_TABLE(tab.colA, ',')) AS s1
  UNION
  SELECT ID, COLA, COLB, TRIM(s2.VALUE::STRING) AS col
  FROM tab
  ,TABLE(SPLIT_TO_TABLE(tab.colB, ',')) AS s2
) AS sub
GROUP BY ID, COLA, COLB
ORDER BY ID;

For sample data:

CREATE OR REPLACE TABLE tab
AS
SELECT 1 AS id, 'dog, cat, mouse' AS colA, 'truck, jeep, lorry' AS colB UNION 
SELECT 2 AS id, 'sparrow' AS colA, 'sparrow, parrot' AS colB;

Output:

---

Sidenote: For storing non-atomic values ARRAY is a better choice:

CREATE OR REPLACE TABLE tab
AS
SELECT 1 AS id, ['dog', 'cat', 'mouse'] AS colA, ['truck', 'jeep', 'lorry'] AS colB UNION 
SELECT 2 AS id, ['sparrow'] AS colA, ['sparrow', 'parrot'] AS colB;

Then combining is a matter of using ARRAY_UNION_AGG:

SELECT ID, ARRAY_UNION_AGG(COL) AS COLC
FROM (
  SELECT ID, COLA AS col FROM tab
  UNION ALL
  SELECT ID, COLB AS col FROM tab
) sub
GROUP BY ID
ORDER BY ID;

Output:

Answer 2

Consider a UNION query:

SELECT 1 AS GrpID, FieldA AS Data FROM tablename
UNION SELECT 2, FieldB FROM tablename;