Oracle 21c

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WITH a (v) AS (
  SELECT LEVEL FROM DUAL CONNECT BY LEVEL < 5
),
b (v) AS (
  SELECT LEVEL FROM DUAL CONNECT BY LEVEL < 5
)
SELECT a.v
  FROM a
       CROSS APPLY (
         SELECT MIN (b.v)
         FROM   b
         WHERE  a.v = b.v
       ) bb


V


1

2

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4


WITH a (v) AS (
  SELECT LEVEL FROM DUAL CONNECT BY LEVEL < 5
),
b (v) AS (
  SELECT LEVEL FROM DUAL CONNECT BY LEVEL < 5
)
SELECT a.v, bb.min_v
  FROM a
       CROSS APPLY (
         SELECT MIN (b.v) As min_v
         FROM   b
         WHERE  a.v = b.v
       ) bb


V
MIN_V


1
1

2
2

3
3

4
4


WITH a (v) AS (
  SELECT LEVEL FROM DUAL CONNECT BY LEVEL < 5
),
b (v) AS (
  SELECT LEVEL FROM DUAL CONNECT BY LEVEL < 5
)
SELECT a.v, bb.min_v
  FROM a
       CROSS APPLY (
         SELECT MIN (b.v) As min_v
         FROM   b
         WHERE  b.v <= a.v
       ) bb


V
MIN_V


1
1

2
1

3
1

4
1