SQL & PL/SQL :: Convert Columns To Rows With Extra Hard Coded Column

I've a query that sum up data from one table. But I've to convert them into rows.

Summary query result.

COL1 COL2 COL3 COL4
1000 2000 3000 4000

Test Table creation script.

CREATE TABLE TEST_TBL
(
COL1 NUMBER(14,2),
COL2 NUMBER(14,2),
COL3 NUMBER(14,2),
COL4 NUMBER(14,2)
) ;

INSERT INTO TEST_TBL VALUES( 1000, 2000, 3000, 4000 ) ;

Expected result

A1 1000
A2 2000
A3 3000
A4 4000

A1, A2, A3, A4 are hard coded fixed values.

I could have done this but not a good idea in case table TEST_TBL is not a single row table but an inline query on 1,00,00,000 records with summary functions. In my table I've a summary query instead of single row table.

SELECT 'A1', COL1 FROM TEST_TBL
UNION ALL
SELECT 'A2', COL2 FROM TEST_TBL
UNION ALL
SELECT 'A3', COL3 FROM TEST_TBL
UNION ALL
SELECT 'A4', COL4 FROM TEST_TBL