SQL における下記の構文に相当します。
SELECT
"col1″,
CASE seq.num
WHEN 0 THEN 'col2'
WHEN 1 THEN 'col3'
ELSE NULL
END AS "label",
CASE seq.num
WHEN 0 THEN CAST("col2" AS varchar)
WHEN 1 THEN CAST("col3" AS varchar)
ELSE NULL
END AS "value"
FROM "iris"
CROSS JOIN
(SELECT 0 AS num
UNION ALL SELECT 1 AS num) AS seq
